顔写真

フカミ シユンスケ
深見 俊輔
Shunsuke Fukami
所属
電気通信研究所 計算システム基盤研究部門 スピントロニクス研究室
職名
教授
学位
  • 博士(工学)(名古屋大学)

  • 修士(工学)(名古屋大学)

経歴 9

  • 2023年4月 ~ 継続中
    東北大学 先端スピントロニクス研究開発センター センター長

  • 2020年1月 ~ 継続中
    東北大学 国際集積エレクトロニクス研究開発センター 教授

  • 2020年1月 ~ 継続中
    東北大学 電気通信研究所 教授

  • 2019年4月 ~ 継続中
    東北大学 材料科学高等研究所 主任研究者

  • 2016年2月 ~ 2019年12月
    東北大学 電気通信研究所 准教授

  • 2015年4月 ~ 2016年1月
    東北大学 省エネルギー・スピントロニクス集積化システムセンター 准教授

  • 2005年4月 ~ 2016年1月
    日本電気株式会社

  • 2014年4月 ~ 2015年3月
    東北大学 国際集積エレクトロニクス研究開発センター 助教

  • 2011年2月 ~ 2014年3月
    東北大学 省エネルギー・スピントロニクス集積化システムセンター 助教

︎全件表示 ︎最初の5件までを表示

学歴 2

  • 名古屋大学 大学院工学研究科 結晶材料工学専攻

    2003年4月 ~ 2005年3月

  • 名古屋大学 工学部 物理工学科

    1999年4月 ~ 2003年3月

所属学協会 3

  • IEEE Magnetics Society

  • 日本磁気学会

  • 応用物理学会

研究キーワード 3

  • 半導体集積回路

  • 磁性材料

  • スピントロニクス

研究分野 1

  • ナノテク・材料 / 応用物性 /

受賞 16

  1. 日本学術振興会賞

    2023年2月 日本学術振興会 新機能スピントロニクス素子の研究開発と新概念コンピューティングへの展開

  2. 日本磁気学会令和4年度業績賞

    2022年9月 公益社団法人日本磁気学会 新機能スピントロニクス素子の開発と革新的情報処理への展開

  3. 丸文研究奨励賞

    2021年3月 一般財団法人丸文財団 トンネル磁気抵抗素子を用いた確率論的コンピューターの原理実証

  4. 優秀論文賞

    2019年9月 応用物理学会 Analogue spin–orbit torque device for artificial-neural-network-based associative memory operation

  5. 「貴金属に関わる研究助成金」ゴールド賞

    2019年3月 田中貴金属記念財団 CoPt系ナノコンポジット材料を用いたアナログナノスピンメモリ素子の創製と脳型情報処理応用

  6. 優秀研究賞

    2018年9月 日本磁気学会 高速メモリ・人工神経回路網応用に向けた不揮発性スピントロニクス素子技術に関する研究

  7. Young Researchers Award

    2018年6月 Asian Union of Magnetics Societies Spin-orbit torque switching and its applications – from high-speed memory to artificial neural network –

  8. 青葉工学振興会賞

    2017年12月 一般財団法人青葉工学振興会 新規スピントロニクス素子の開拓と集積回路・脳型情報処理応用

  9. 2nd ImPACT International Symposium on Spintronic Memory, Circuit and Storage, Best Poster Award

    2017年9月 Spin-orbit torque induced magnetization switching in nano-scale Ta/CoFeB/MgO dots

  10. DPS Paper Award

    2016年11月 38th International Symposium on Dry Process(DPS2016) Organizing Committee Plasma process induced physical damages on multilayered magnetic films for magnetic domain wall motion

  11. 原田研究奨励賞

    2015年7月 本多記念会 高性能3端子スピントロニクス素子の研究開発

  12. 文部科学大臣表彰 若手科学者賞

    2015年4月 文部科学省 電流誘起磁壁移動とその集積回路応用に関する研究

  13. 応用物理学会講演奨励賞

    2014年9月 応用物理学会 ナノ細線中の磁壁の熱安定性としきい電流

  14. 船井研究奨励賞

    2014年4月 船井情報科学振興財団 高性能低消費電力論理集積回路の実現に向けた電流誘起磁壁移動デバイスの研究開発

  15. RIEC Award東北大学研究者賞

    2013年11月21日 電気通信工学振興会

  16. 応用物理学会論文賞

    2012年9月11日 応用物理学会 Control of Multiple Magnetic Domain Walls by Current in a Co/Ni Nano-Wire

︎全件表示 ︎最初の5件までを表示

論文 241

  1. Double-Free-Layer Stochastic Magnetic Tunnel Junctions with Synthetic Antiferromagnets

    Kemal Selcuk, Shun Kanai, Rikuto Ota, Hideo Ohno, Shunsuke Fukami, Kerem Y. Camsari

    arXiv 2311.06642 2023年11月11日

    DOI: 10.48550/arXiv.2311.06642  

  2. Handedness anomaly in a non-collinear antiferromagnet under spin–orbit torque

    Ju-Young Yoon, Pengxiang Zhang, Chung-Tao Chou, Yutaro Takeuchi, Tomohiro Uchimura, Justin T. Hou, Jiahao Han, Shun Kanai, Hideo Ohno, Shunsuke Fukami, Luqiao Liu

    Nature Materials 22 (9) 1106-1113 2023年8月3日

    出版者・発行元:Springer Science and Business Media LLC

    DOI: 10.1038/s41563-023-01620-2  

    ISSN:1476-1122

    eISSN:1476-4660

  3. Nonlinear conductance in nanoscale CoFeB/MgO magnetic tunnel junctions with perpendicular easy axis 査読有り

    Motoya Shinozaki, Junta Igarashi, Shuichi Iwakiri, Takahito Kitada, Keisuke Hayakawa, Butsurin Jinnai, Tomohiro Otsuka, Shunsuke Fukami, Kensuke Kobayashi, Hideo Ohno

    Physical Review B 107 (9) 2023年3月30日

    DOI: 10.1103/PhysRevB.107.094436  

    ISSN:2469-9950

    eISSN:2469-9969

    詳細を見る 詳細を閉じる

    Magnetic tunnel junctions (MTJ) exhibit spin-dependent conductance that governs their performance in various applications. While the transport characteristics are known to show nonlinearity, their behavior and underlying mechanism have not yet understood well. Here we investigate nonlinear conductance at a low bias regime in nanoscale MTJs with a perpendicular magnetic easy axis and various junction sizes, by measuring current-voltage (IV) characteristics and ferromagnetic resonance. We evaluate IV properties as I=G1V+G2V2+G3V3 under various external magnetic fields and examine the correlations among G1, G2, and G3. We find that G2 increases with decrease in the junction size, G3 has a negative correlation with G1, and δG3/δG1(=k) has a positive correlation with G2. These results can be explained by considering the spin flip during the tunneling and a modulation of material properties at the device edge caused by the nanofabrication process. Ferromagnetic resonance measurements support the physical picture suggested by the transport measurements. Our findings shed light on the mechanism of electron transport in nanoscale MTJs and facilitate the establishment of a rigorous model describing their nonlinear conductance.

  4. Thermal stability of non-collinear antiferromagnetic Mn<inf>3</inf>Sn nanodot

    Yuma Sato, Yutaro Takeuchi, Yuta Yamane, Ju Young Yoon, Shun Kanai, Jun'Ichi Ieda, Hideo Ohno, Shunsuke Fukami

    Applied Physics Letters 122 (12) 2023年3月20日

    DOI: 10.1063/5.0135709  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    D019-Mn3Sn, an antiferromagnet having a non-collinear spin structure in a kagome lattice, has attracted great attention owing to various intriguing properties such as large anomalous Hall effect. Stability of a magnetic state against thermal fluctuation, characterized in general by the thermal stability factor Δ, has been well studied in ferromagnetic systems but not for antiferromagnets. Here, we study Δ of the antiferromagnetic Mn3Sn nanodots as a function of their diameter D. To quantify Δ, we measure the switching probability as a function of the pulse-field amplitude and analyze the results based on a model taking account of two and sixfold magnetic anisotropies in the kagome plane. We observe no significant change in Δ down to D = 300 nm below which it decreases with D. The obtained D dependence is well explained by a single-domain and nucleation-mediated reversal models. These findings provide a basis to understand the thermal fluctuation and reversal mechanism of antiferromagnets for device applications.

  5. A full-stack view of probabilistic computing with p-bits: devices, architectures and algorithms

    Shuvro Chowdhury, Andrea Grimaldi, Navid Anjum Aadit, Shaila Niazi, Masoud Mohseni, Shun Kanai, Hideo Ohno, Shunsuke Fukami, Luke Theogarajan, Giovanni Finocchio, Supriyo Datta, Kerem Y. Camsari

    IEEE Journal on Exploratory Solid-State Computational Devices and Circuits 2023年

    DOI: 10.1109/JXCDC.2023.3256981  

    eISSN:2329-9231

    詳細を見る 詳細を閉じる

    The transistor celebrated its 75th birthday in 2022. The continued scaling of the transistor defined by Moore&#x2019;s Law continues, albeit at a slower pace. Meanwhile, computing demands and energy consumption required by modern artificial intelligence (AI) algorithms have skyrocketed. As an alternative to scaling transistors for general-purpose computing, the integration of transistors with unconventional technologies has emerged as a promising path for domain-specific computing. In this article, we provide a full-stack review of probabilistic computing with p-bits as a representative example of the energy-efficient and domain-specific computing movement. We argue that p-bits could be used to build energy-efficient probabilistic systems, tailored for probabilistic algorithms and applications. From hardware, architecture, and algorithmic perspectives, we outline the main applications of probabilistic computers ranging from probabilistic machine learning and AI to combinatorial optimization and quantum simulation. Combining emerging nanodevices with the existing CMOS ecosystem will lead to probabilistic computers with orders of magnitude improvements in energy efficiency and probabilistic sampling, potentially unlocking previously unexplored regimes for powerful probabilistic algorithms.

  6. External-Field-Robust Stochastic Magnetic Tunnel Junctions Using a Free Layer with Synthetic Antiferromagnetic Coupling

    Keito Kobayashi, Keisuke Hayakawa, Junta Igarashi, William A. Borders, Shun Kanai, Hideo Ohno, Shunsuke Fukami

    Physical Review Applied 18 (5) 2022年11月29日

    出版者・発行元:American Physical Society (APS)

    DOI: 10.1103/physrevapplied.18.054085  

    eISSN:2331-7019

    詳細を見る 詳細を閉じる

    The stochastic magnetic tunnel junction (MTJ), the resistance of which fluctuates in time between low and high states under thermal fluctuation, is expected to serve as a key element in probabilistic computers. For reliable operation and versatile application, one needs to address the challenge that the relaxation time in each state should be virtually independent of external magnetic fields in the range of, for example, several mT. In this research, we fabricate in-plane easy-axis elliptical stochastic MTJs with a synthetic antiferromagnetic (SAF) free layer and examine the robustness of their properties against external fields while comparing them with stochastic MTJs with a conventional single ferromagnetic structure. We show that the MTJ with a SAF free layer shows more robust relaxation times against fields applied along the easy- and hard-axis directions. The results are reproduced with a macrospin simulation, from which design guidelines for robust stochastic MTJs targeting probabilistic computers are discussed.

  7. Large Exotic Spin Torques in Antiferromagnetic Iron Rhodium

    Jonathan Gibbons, Takaaki Dohi, Vivek P. Amin, Fei Xue, Haowen Ren, Jun-Wen Xu, Hanu Arava, Soho Shim, Hilal Saglam, Yuzi Liu, John E. Pearson, Nadya Mason, Amanda K. Petford-Long, Paul M. Haney, Mark D. Stiles, Eric E. Fullerton, Andrew D. Kent, Shunsuke Fukami, Axel Hoffmann

    Physical Review Applied 18 (2) 2022年8月29日

    出版者・発行元:American Physical Society (APS)

    DOI: 10.1103/physrevapplied.18.024075  

    eISSN:2331-7019

    詳細を見る 詳細を閉じる

    Spin torque is a promising tool for driving magnetization dynamics for computing technologies. These torques can be easily produced by spin-orbit effects, but for most conventional spin source materials, a high degree of crystal symmetry limits the geometry of the spin torques produced. Magnetic ordering is one way to reduce the symmetry of a material and allow exotic torques, and antiferromagnets are particularly promising because they are robust against external fields. We present spin torque ferromagnetic resonance (ST-FMR) measurements and second harmonic Hall measurements characterizing the spin torques in antiferromagnetic iron rhodium alloy. We report extremely large, strongly temperature-dependent exotic spin torques with a geometry apparently defined by the magnetic ordering direction. We find the spin torque efficiency of iron rhodium to be (207 ± 94)% at 170 K and (88 ± 32)% at room temperature. We support our conclusions with theoretical calculations showing how the antiferromagnetic ordering in iron rhodium gives rise to such exotic torques.

  8. Anisotropic magnetotransport in the layered antiferromagnet TaFe1.25Te3

    Rajeswari Roy Chowdhury, Samik DuttaGupta, Chandan Patra, Anshu Kataria, Shunsuke Fukami, Ravi Prakash Singh

    Physical Review Materials 6 (8) 2022年8月12日

    出版者・発行元:American Physical Society (APS)

    DOI: 10.1103/physrevmaterials.6.084408  

    eISSN:2475-9953

    詳細を見る 詳細を閉じる

    The discovery of fascinating ways to control and manipulate antiferromagnetic materials have garnered considerable attention as an attractive platform to explore novel spintronic phenomena and functionalities. Layered antiferromagnets (AFMs) exhibiting interesting magnetic structures can serve as an attractive starting point to establish novel functionalities down to the two-dimensional limit. In this work, we explore the magnetoresistive properties of the spin-ladder AFM TaFe1.25Te3. Magnetization studies reveal an anisotropic magnetic behavior resulting in the stabilization of a spin-flop configuration for H (10-1) plane (i.e., out-of-plane direction). Angle-dependent longitudinal and transverse magnetoresistances show an unusual anharmonic behavior. A significant anisotropic enhancement of magnetoresistance when H (10-1) plane compared to H|| (10-1) directions has been observed. The present results deepen our understanding of the magnetoresistive properties of low-dimensional layered AFMs, and point towards the possibility of utilizing these novel material systems for antiferromagnetic spintronics.

  9. Local bifurcation with spin-transfer torque in superparamagnetic tunnel junctions

    Takuya Funatsu, Shun Kanai, Jun’ichi Ieda, Shunsuke Fukami, Hideo Ohno

    Nature Communications 13 (1) 2022年7月

    DOI: 10.1038/s41467-022-31788-1  

    eISSN:2041-1723

    詳細を見る 詳細を閉じる

    Modulation of the energy landscape by external perturbations governs various thermally-activated phenomena, described by the Arrhenius law. Thermal fluctuation of nanoscale magnetic tunnel junctions with spin-transfer torque (STT) shows promise for unconventional computing, whereas its rigorous representation, based on the Néel-Arrhenius law, has been controversial. In particular, the exponents for thermally-activated switching rate therein, have been inaccessible with conventional thermally-stable nanomagnets with decade-long retention time. Here we approach the Néel-Arrhenius law with STT utilising superparamagnetic tunnel junctions that have high sensitivity to external perturbations and determine the exponents through several independent measurements including homodyne-detected ferromagnetic resonance, nanosecond STT switching, and random telegraph noise. Furthermore, we show that the results are comprehensively described by a concept of local bifurcation observed in various physical systems. The findings demonstrate the capability of superparamagnetic tunnel junction as a useful tester for statistical physics as well as sophisticated engineering of probabilistic computing hardware with a rigorous mathematical foundation.

  10. Large Antisymmetric Interlayer Exchange Coupling Enabling Perpendicular Magnetization Switching by an In-Plane Magnetic Field 査読有り

    Hiroto Masuda, Takeshi Seki, Yuta Yamane, Rajkumar Modak, Ken-ichi Uchida, Jun’ichi Ieda, Yong-Chang Lau, Shunsuke Fukami, Koki Takanashi

    Physical Review Applied 17 (5) 054036-1-054036-9 2022年5月

    DOI: 10.1103/PhysRevApplied.17.054036  

    eISSN:2331-7019

  11. Observation of domain structure in non-collinear antiferromagnetic Mn3Sn thin films by magneto-optical Kerr effect

    Tomohiro Uchimura, Ju-Young Yoon, Yuma Sato, Yutaro Takeuchi, Shun Kanai, Ryota Takechi, Keisuke Kishi, Yuta Yamane, Samik DuttaGupta, Jun'ichi Ieda, Hideo Ohno, Shunsuke Fukami

    APPLIED PHYSICS LETTERS 120 (17) 2022年4月

    出版者・発行元:AIP Publishing

    DOI: 10.1063/5.0089355  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    We perform hysteresis-loop measurement and domain imaging for ( 1 (1) over bar 00 )-oriented D0(19)-Mn3+xSn1-x (-0.11 <= x <= 0.14) thin films using the magneto-optical Kerr effect (MOKE) and compare it with the anomalous Hall effect (AHE) measurement. We obtain a large Kerr rotation angle of 10 mdeg, comparable with bulk single-crystal Mn3Sn. The composition x dependence of AHE and MOKE shows a similar trend, suggesting the same origin, i.e., the non-vanishing Berry curvature in the momentum space. Magnetic domain observation at the saturated state shows that x dependence of AHE and MOKE is explained by the amount of the reversible area that crucially depends on the crystalline structure of the film. Furthermore, in-depth observation of the reversal process reveals that the reversal starts with nucleation of sub-micrometer-scale domains dispersed in the film, followed by domain expansion, where the domain wall preferentially propagates along the [ 11(2) over bar 0 ] direction. Our study provides a basic understanding of the spatial evolution of the reversal of the chiral-spin structure in non-collinear antiferromagnetic thin films.& nbsp;Published under an exclusive license by AIP Publishing.

  12. Theory of Emergent Inductance with Spin-Orbit Coupling Effects

    Yuta Yamane, Shunsuke Fukami, Jun'ichi Ieda

    PHYSICAL REVIEW LETTERS 128 (14) 2022年4月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevLett.128.147201  

    ISSN:0031-9007

    eISSN:1079-7114

    詳細を見る 詳細を閉じる

    We extend the theory of emergent inductance, which has recently been discovered in spiral magnets, to arbitrary magnetic textures by taking into account spin-orbit couplings arising in the absence of spatial inversion symmetry. We propose a new concept of spin-orbit emergent inductance, which can be formulated as originating from a dynamical Aharonov-Casher phase of an electron in ferromagnets. The spin-orbit emergent inductance universally arises in the coexistence of magnetism and the spin-orbit couplings, even with spatially uniform magnetization, allowing its stable operation in wide ranges of temperature and frequency. Revisiting the widely studied systems involving ferromagnets with spatial inversion asymmetry, with the new perspective offered by our work, will lead to opening a new paradigm in the study of spin-orbit physics and the spintronics-based power management in ultrawideband frequency range.

  13. Nanometer-thin L10-MnAl film with B2-CoAl underlayer for high-speed and high-density STT-MRAM: Structure and magnetic properties

    Yutaro Takeuchi, Ryotaro Okuda, Junta Igarashi, Butsurin Jinnai, Takaharu Saino, Shoji Ikeda, Shunsuke Fukami, Hideo Ohno

    Applied Physics Letters 120 (5) 2022年1月31日

    出版者・発行元:AIP Publishing

    DOI: 10.1063/5.0077874  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    The material development of magnetic tunnel junction with a perpendicular easy axis is in great demand to advance spin-transfer torque magnetoresistive random access memory (STT-MRAM) technologies. To realize high-speed and high-density STT-MRAM, a thin-film magnetic material with large perpendicular anisotropy and small spontaneous magnetization has great potential. Here, we develop a thin-film deposition technique for a-few-nanometer-thin L10-MnAl by sputtering and investigate its structure and magnetic properties. Utilization of the B2-CoAl buffer layer allows us to grow L10-MnAl with a large crystalline anisotropy of 8.5 × 105 J/m3, the small spontaneous magnetization of 0.62 T, and the tolerance for 400 °C annealing even at the MnAl thickness of 2 nm. We calculate the device properties based on the obtained material parameters and find that high retention properties, high-speed switching, and low write-error rate can be obtained at the single-digit-nm region, which are not readily achieved by conventional material systems. The results show the potential of L10-MnAl for high-density and high-speed STT-MRAM.

  14. Experimental evaluation of simulated quantum annealing with MTJ-augmented p-bits

    Andrea Grimaldi, Kemal Selcuk, Navid Anjum Aadit, Keito Kobayashi, Qixuan Cao, Shuvro Chowdhury, Giovanni Finocchio, Shun Kanai, Hideo Ohno, Shunsuke Fukami, Kerem Y. Camsari

    Technical Digest - International Electron Devices Meeting, IEDM 2022-December 2241-2244 2022年

    DOI: 10.1109/IEDM45625.2022.10019530  

    ISSN:0163-1918

    詳細を見る 詳細を閉じる

    The slowing down of Moore's Law has created an exciting new era of electronics, leading to the emergence of various types of CMOS+X devices and architectures. Here, we present the first experimental demonstration of a probabilistic computer where a stochastic magnetic tunnel junction (sMTJ) drives a powerful CMOS-based field programmable gate array (FPGA) in a heterogeneous compute fabric. We use our machine to experimentally evaluate the simulated quantum annealing (SQA) algorithm, known to closely mimic the behavior of D-Wave's quantum annealers which implement the transverse field Ising model (TFIM). Our machine matches the exact solution of the TFIM where p-bits in the FPGA are asynchronously driven by the stochastic dynamics of a magnetic tunnel junction. To compare the performance of SQA against classical annealing (CA) in hard combinatorial optimization at large scale, we also design a fully digital emulator of our asynchronous architecture in the FPGA. Our digital system uses 7,085 p-bits to factor up to 26-bit integers and is about 10X faster than optimized Tensor (TPU) and Graphics Processing Units (GPU) at lower power. Surprisingly, we find that the additional replica networks necessary for SQA do not lead to appreciably better performance over an optimized CA that is using the same computational resources. The systematic evaluation of the SQA algorithm we present will be relevant for other types of accelerators, such as photonic or electronic Ising machines and the integrated scaling of our CMOS + sMTJ architecture could lead to orders of magnitude further improvements over TPU and GPUs, according to experimentally-validated projections.

  15. Modification of unconventional Hall effect with doping at the nonmagnetic site in a two-dimensional van der Waals ferromagnet

    Rajeswari Roy Chowdhury, Chandan Patra, Samik DuttaGupta, Sayooj Satheesh, Shovan Dan, Shunsuke Fukami, Ravi Prakash Singh

    Physical Review Materials 6 (1) 2022年1月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevMaterials.6.014002  

    ISSN:2475-9953

    eISSN:2475-9953

    詳細を見る 詳細を閉じる

    Two-dimensional (2D) van der Waals (vdW) magnets have garnered considerable attention owing to the existence of magnetic order down to atomic dimensions, flexibility towards interface engineering and unconventional magnetoresistive properties, offering an attractive platform to explore novel phenomena and functionalities, prospective for spintronic or quantum information devices. Among the promising candidates, vdW ferromagnet (FM) Fe3GeTe2 shows an unusual magnetotransport behavior, tunable by doping at the magnetic (Fe) site, and tentatively arising from complicated underlying spin texture configurations. In this work, we explore an alternative route towards manipulation of magnetotransport properties without directly affecting the magnetic site i.e., by doping at the nonmagnetic (Ge) site of Fe3(Ge,As)Te2. Interestingly, doping at the non-magnetic (Ge) site results in an unconventional Hall effect whose strength was considerably modified by increasing As concentration, tentatively attributed to underlying emergent electromagnetic behavior, demonstrating an alternate direction towards tailoring of underlying interactions without perturbing the magnetic (Fe) site in 2D vdW magnetic materials.

  16. Hardware-Aware In Situ Learning Based on Stochastic Magnetic Tunnel Junctions

    Jan Kaiser, William A. Borders, Kerem Y. Camsari, Shunsuke Fukami, Hideo Ohno, Supriyo Datta

    Physical Review Applied 17 (1) 2022年1月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevApplied.17.014016  

    ISSN:2331-7019

    eISSN:2331-7019

    詳細を見る 詳細を閉じる

    One of the big challenges of current electronics is the design and implementation of hardware neural networks that perform fast and energy-efficient machine learning. Spintronics is a promising catalyst for this field with the capabilities of nanosecond operation and compatibility with existing microelectronics. Considering large-scale, viable neuromorphic systems however, variability of device properties is a serious concern. In this paper, we show an autonomously operating circuit that performs hardware-aware machine learning utilizing probabilistic neurons built with stochastic magnetic tunnel junctions. We show that in situ learning of weights and biases in a Boltzmann machine can counter device-to-device variations and learn the probability distribution of meaningful operations such as a full adder. This scalable autonomously operating learning circuit using spintronics-based neurons could be especially of interest for standalone artificial-intelligence devices capable of fast and efficient learning at the edge.

  17. Memristive control of mutual spin Hall nano-oscillator synchronization for neuromorphic computing

    Mohammad Zahedinejad, Himanshu Fulara, Roman Khymyn, Afshin Houshang, Mykola Dvornik, Shunsuke Fukami, Shun Kanai, Hideo Ohno, Johan Åkerman

    Nature Materials 21 (1) 81-87 2022年1月

    出版者・発行元:NATURE PORTFOLIO

    DOI: 10.1038/s41563-021-01153-6  

    ISSN:1476-1122

    eISSN:1476-4660

    詳細を見る 詳細を閉じる

    Synchronization of large spin Hall nano-oscillator (SHNO) arrays is an appealing approach toward ultrafast non-conventional computing. However, interfacing to the array, tuning its individual oscillators and providing built-in memory units remain substantial challenges. Here, we address these challenges using memristive gating of W/CoFeB/MgO/AlOx-based SHNOs. In its high resistance state, the memristor modulates the perpendicular magnetic anisotropy at the CoFeB/MgO interface by the applied electric field. In its low resistance state the memristor adds or subtracts current to the SHNO drive. Both electric field and current control affect the SHNO auto-oscillation mode and frequency, allowing us to reversibly turn on/off mutual synchronization in chains of four SHNOs. We also demonstrate that two individually controlled memristors can be used to tune a four-SHNO chain into differently synchronized states. Memristor gating is therefore an efficient approach to input, tune and store the state of SHNO arrays for non-conventional computing models.

  18. Temperature dependence of intrinsic critical current in perpendicular easy axis CoFeB/MgO magnetic tunnel junctions

    Yutaro Takeuchi, Eli Christopher I. Enobio, Butsurin Jinnai, Hideo Sato, Shunsuke Fukami, Hideo Ohno

    Applied Physics Letters 119 (24) 2021年12月13日

    出版者・発行元:AIP Publishing

    DOI: 10.1063/5.0072957  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    Current induced magnetization switching in CoFeB/MgO-based magnetic tunnel junctions (MTJs) with a perpendicular easy axis is studied above room temperature. The intrinsic critical current IC0 of the MTJs decreases with increasing temperature. From a vector-network-analyzer ferromagnetic resonance measurement with a heating system, temperature dependence of magnetic anisotropy and damping constant is evaluated. We find that the reduction of IC0 at elevated temperature is mainly due to a decrease in magnetic anisotropy. A slight increase in the damping constant with temperature rise is also observed, consistent with the mechanism considering electron scattering through the inter-band transition.

  19. Unconventional Hall effect and its variation with Co-doping in van der Waals Fe3GeTe2

    Rajeswari Roy Chowdhury, Samik DuttaGupta, Chandan Patra, Oleg A. Tretiakov, Sudarshan Sharma, Shunsuke Fukami, Hideo Ohno, Ravi Prakash Singh

    Scientific Reports 11 (1) 2021年12月

    出版者・発行元:Springer Science and Business Media LLC

    DOI: 10.1038/s41598-021-93402-6  

    ISSN:2045-2322

    eISSN:2045-2322

    詳細を見る 詳細を閉じる

    <title>Abstract</title>Two-dimensional (2D) van der Waals (vdW) magnetic materials have attracted a lot of attention owing to the stabilization of long range magnetic order down to atomic dimensions, and the prospect of novel spintronic devices with unique functionalities. The clarification of the magnetoresistive properties and its correlation to the underlying magnetic configurations is essential for 2D vdW-based spintronic devices. Here, the effect of Co-doping on the magnetic and magnetotransport properties of Fe<sub>3</sub>GeTe<sub>2</sub> have been investigated. Magnetotransport measurements reveal an unusual Hall effect behavior whose strength was considerably modified by Co-doping and attributed to arise from the underlying complicated spin textures. The present results provide a clue to tailoring of the underlying interactions necessary for the realization of a variety of unconventional spin textures for 2D vdW FM-based spintronics.

  20. Sigmoidal curves of stochastic magnetic tunnel junctions with perpendicular easy axis

    Keito Kobayashi, William A. Borders, Shun Kanai, Keisuke Hayakawa, Hideo Ohno, Shunsuke Fukami

    Applied Physics Letters 119 (13) 2021年9月27日

    出版者・発行元:AIP Publishing

    DOI: 10.1063/5.0065919  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    We investigate the physical mechanism governing the sigmoid-like time-averaged response of stochastic magnetic tunnel junctions (s-MTJ), which is a promising building block for probabilistic computers. We measure the time-averaged resistance of perpendicular easy-axis s-MTJs with various free-layer thicknesses and diameters as functions of an external magnetic field and current. The time-averaged response shows no significant dependence on the free-layer thickness, whereas significantly varies with the diameter. Based on the Néel-Arrhenius law, we derive an analytical expression of the time-averaged response against both the magnetic field and current and discuss the underlying mechanism accounting for the obtained results. We show that the experimental results are well explained by considering magnetically active and electrically active volumes of the superparamagnetic free layer in s-MTJs. The obtained finding provides an important design guideline of s-MTJs for probabilistic computers.

  21. Roadmap of Spin-Orbit Torques

    Qiming Shao, Peng Li, Luqiao Liu, Hyunsoo Yang, Shunsuke Fukami, Armin Razavi, Hao Wu, Kang Wang, Frank Freimuth, Yuriy Mokrousov, Mark D. Stiles, Satoru Emori, Axel Hoffmann, Johan Akerman, Kaushik Roy, Jian Ping Wang, See Hun Yang, Kevin Garello, Wei Zhang

    IEEE Transactions on Magnetics 57 (7) 2021年7月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2021.3078583  

    ISSN:0018-9464

    eISSN:1941-0069

    詳細を見る 詳細を閉じる

    Spin-orbit torque (SOT) is an emerging technology that enables the efficient manipulation of spintronic devices. The initial processes of interest in SOTs involved electric fields, spin-orbit coupling, conduction electron spins, and magnetization. More recently, interest has grown to include a variety of other processes that include phonons, magnons, or heat. Over the past decade, many materials have been explored to achieve a larger SOT efficiency. Recently, holistic design to maximize the performance of SOT devices has extended material research from a nonmagnetic layer to a magnetic layer. The rapid development of SOT has spurred a variety of SOT-based applications. In this article, we first review the theories of SOTs by introducing the various mechanisms thought to generate or control SOTs, such as the spin Hall effect, the Rashba-Edelstein effect, the orbital Hall effect, thermal gradients, magnons, and strain effects. Then, we discuss the materials that enable these effects, including metals, metallic alloys, topological insulators, 2-D materials, and complex oxides. We also discuss the important roles in SOT devices of different types of magnetic layers, such as magnetic insulators, antiferromagnets, and ferrimagnets. Afterward, we discuss device applications utilizing SOTs. We discuss and compare three- and two-terminal SOT-magnetoresistive random access memories (MRAMs); we mention various schemes to eliminate the need for an external field. We provide technological application considerations for SOT-MRAM and give perspectives on SOT-based neuromorphic devices and circuits. In addition to SOT-MRAM, we present SOT-based spintronic terahertz generators, nano-oscillators, and domain-wall and skyrmion racetrack memories. This article aims to achieve a comprehensive review of SOT theory, materials, and applications, guiding future SOT development in both the academic and industrial sectors.

  22. Magnetization processes and magnetic domain structures in Ta/CoFeB/MgO stacks

    A. K. Dhiman, T. Dohi, W. Dobrogowski, Z. Kurant, I. Sveklo, S. Fukami, H. Ohno, A. Maziewski

    Journal of Magnetism and Magnetic Materials 529 2021年7月1日

    DOI: 10.1016/j.jmmm.2020.167699  

    ISSN:0304-8853

    詳細を見る 詳細を閉じる

    Magnetization processes and magnetic domain structures in Ta/CoFeB/MgO stacks were studied in a series of samples with various CoFeB thicknesses d ranging from 1.24 to 1.60 nm with a step of 0.04 nm, using polar magneto-optical Kerr effect (PMOKE) magnetometry and microscopy. Thickness dependence of the magnetic anisotropy was evaluated and the first and second order anisotropy constants were quantified for each thickness. Accordingly, this dependence was deduced to result in magnetization reorientation from out-of-plane to in-plane through an easy-cone magnetization region (1.39 nm ≤ d ≤ 1.41 nm) as d was increased. PMOKE imaging of the magnetization reversal processes for stacks with out-of-plane easy axis indicated both a significant increase of the density of nucleation centers and a change in domain morphology with increasing d up to the magnetization reorientation thickness. Magnetization reversal dynamics was described by a thermal activation model consistent with a Barkhausen length of about 120 nm. The thinnest films with d = 1.24 and 1.28 nm exhibited straightened narrow stripe domains resulting from magnetic dipolar repulsion. A thorough study of narrow stripe domains was performed via direct and indirect magnetization reversal processes. The application of such structures as spin wave nano-channels could be promising.

  23. Influence of domain wall anisotropy on the current-induced hysteresis loop shift for quantification of the Dzyaloshinskii-Moriya interaction

    Takaaki Dohi, Shunsuke Fukami, Hideo Ohno

    Physical Review B 103 (21) 2021年6月29日

    出版者・発行元:American Physical Society (APS)

    DOI: 10.1103/physrevb.103.214450  

    ISSN:2469-9950

    eISSN:2469-9969

    詳細を見る 詳細を閉じる

    Using several material systems with various magnitudes of the interfacial Dzyaloshinskii-Moriya interaction (DMI), we elucidate a critical influence of domain wall (DW) anisotropy on the current-induced hysteresis loop shift scheme widely employed to determine the magnitude of the Dzyaloshinskii-Moriya effective field (HDMI). Taking into account the DW anisotropy in the analysis of the hysteresis loop shift, which has not been included in the original model [Phys. Rev. B 93, 144409 (2016)10.1103/PhysRevB.93.144409], we show that it provides quantitative agreement of HDMI with that determined from an asymmetric bubble expansion technique for small DMI material systems. For large DMI systems, the DW anisotropy gives rise to nonlinearity in the response of spin-orbit torque efficiency to the in-plane magnetic field, from which HDMI can be determined. The consequence of the directions of DW motion in the Hall device on the current-induced shift of the hysteresis loop is also discussed. The present findings deliver important insights for reliable evaluation of DMI, which are of significance in spintronics with chiral objects.

  24. Correlation of anomalous Hall effect with structural parameters and magnetic ordering in Mn3+xSn1−x thin films

    Ju-Young Yoon, Yutaro Takeuchi, Samik DuttaGupta, Yuta Yamane, Shun Kanai, Jun’ichi Ieda, Hideo Ohno, Shunsuke Fukami

    AIP Advances 11 (6) 065318-065318 2021年6月1日

    出版者・発行元:AIP Publishing

    DOI: 10.1063/5.0043192  

    eISSN:2158-3226

    詳細を見る 詳細を閉じる

    We investigate the relationship between structural parameters, magnetic ordering, and the anomalous Hall effect (AHE) of Mn3+xSn1-x (-0.42 ≤ x ≤ +0.23) thin films annealed at various temperatures Ta. The crystal structure changes with x and Ta, and at Ta ≥ 500 °C near the stoichiometric composition (-0.08 ≤ x ≤ +0.04), epitaxial single-phase D019-Mn3+xSn1-x(101̄0) is obtained. At room temperature, a larger AHE is obtained when the single-phase epitaxial Mn3Sn with the lattice constant closer to that of bulk is formed. The temperature dependence of the AHE shows different behaviors depending on Ta and can be explained by considering the variation of magnetic ordering. A close inspection into the temperature and composition dependence suggests a variation of magnetic phase transition temperature with composition and/or a possible correlation between the AHE and Fermi level position with respect to the Weyl points. Our comprehensive study on (101̄0)-oriented epitaxial Mn3Sn thin films would provide the basis for utilizing the unique functionalities of non-collinear antiferromagnetic materials.

  25. Electrically connected spin-torque oscillators array for 2.4GHz WiFi band transmission and energy harvesting

    Raghav Sharma, Rahul Mishra, Tung Ngo, Yong-Xin Guo, Shunsuke Fukami, Hideo Sato, Hideo Ohno, Hyunsoo Yang

    NATURE COMMUNICATIONS 12 (1) 2021年5月

    出版者・発行元:NATURE RESEARCH

    DOI: 10.1038/s41467-021-23181-1  

    ISSN:2041-1723

    eISSN:2041-1723

    詳細を見る 詳細を閉じる

    The mutual synchronization of spin-torque oscillators (STOs) is critical for communication, energy harvesting and neuromorphic applications. Short range magnetic coupling-based synchronization has spatial restrictions (few mu m), whereas the long-range electrical synchronization using vortex STOs has limited frequency responses in hundreds MHz (<500MHz), restricting them for on-chip GHz-range applications. Here, we demonstrate electrical synchronization of four non-vortex uniformly-magnetized STOs using a single common current source in both parallel and series configurations at 2.4GHz band, resolving the frequency-area quandary for designing STO based on-chip communication systems. Under injection locking, synchronized STOs demonstrate an excellent time-domain stability and substantially improved phase noise performance. By integrating the electrically connected eight STOs, we demonstrate the battery-free energy-harvesting system by utilizing the wireless radio-frequency energy to power electronic devices such as LEDs. Our results highlight the significance of electrical topology (series vs. parallel) while designing an on-chip STOs system. Spin torque oscillators (STOs) are attractive potential alternative for many high frequency applications, due to their small area and CMOS compatibility. Here, Sharma et al succeed in the electrical synchronization of four STOs, and use their setup to demonstrate wireless and battery-free energy harvesting using eight STOs.

  26. Chiral-spin rotation of non-collinear antiferromagnet by spin-orbit torque

    Yutaro Takeuchi, Yuta Yamane, Ju-Young Yoon, Ryuichi Itoh, Butsurin Jinnai, Shun Kanai, Jun'ichi Ieda, Shunsuke Fukami, Hideo Ohno

    NATURE MATERIALS 20 (10) 1364-1370 2021年5月

    出版者・発行元:NATURE RESEARCH

    DOI: 10.1038/s41563-021-01005-3  

    ISSN:1476-1122

    eISSN:1476-4660

    詳細を見る 詳細を閉じる

    Electrical manipulation of magnetic materials by current-induced spin torque constitutes the basis of spintronics. Here, we show an unconventional response to spin-orbit torque of a non-collinear antiferromagnet Mn3Sn, which has attracted attention owing to its large anomalous Hall effect despite a vanishingly small net magnetization. In epitaxial heavy-metal/Mn3Sn heterostructures, we observe a characteristic fluctuation of the Hall resistance under the application of electric current. This observation is explained by a rotation of the chiral-spin structure of Mn3Sn driven by spin-orbit torque. We find that the variation of the magnitude of anomalous Hall effect fluctuation with sample size correlates with the number of magnetic domains in the Mn3Sn layer. In addition, the dependence of the critical current on Mn3Sn layer thickness reveals that spin-orbit torque generated by small current densities, below 20 MA cm(-2), effectively acts on the chiral-spin structure even in Mn3Sn layers that are thicker than 20 nm. The results provide additional pathways for electrical manipulation of magnetic materials.Current-induced rotation in epitaxial films of the non-collinear antiferromagnet Mn3Sn is investigated.

  27. Double-Free-Layer Magnetic Tunnel Junctions for Probabilistic Bits

    Kerem Y. Camsari, Mustafa Mert Torunbalci, William A. Borders, Hideo Ohno, Shunsuke Fukami

    PHYSICAL REVIEW APPLIED 15 (4) 2021年4月

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevApplied.15.044049  

    ISSN:2331-7019

    eISSN:2331-7019

    詳細を見る 詳細を閉じる

    Naturally random devices that exploit ambient thermal noise have recently attracted attention as hardware primitives for accelerating probabilistic computing applications. One such approach is to use a low barrier nanomagnet as the free layer of a magnetic tunnel junction (MTJ), the magnetic fluctuations of which are converted to resistance fluctuations in the presence of a stable fixed layer. Here, we propose and theoretically analyze a MTJ with no fixed layers but two free layers that are circularly shaped disk magnets. We use an experimentally benchmarked model that accounts for finite-temperature magnetization dynamics, bias-dependent charge, and spin-polarized currents as well as the dipolar coupling between the free layers. We obtain analytical results for statistical averages of fluctuations that are in good agreement with the numerical model. We find that the free layers with low diameters fluctuate to randomize the resistance of the MTJ in an approximately bias-independent manner. We show how such MTJs can be used to build a binary stochastic neuron (or ap-bit) in hardware. Unlike earlier stochastic MTJs that need to operate at a specific bias point to produce random fluctuations, the proposed design can be random for a wide range of bias values, independent of spin-transfer-torque pinning. Moreover, in the absence of a carefully optimized stabled fixed layer, the symmetric double-free-layer stack can be manufactured using present-day magnetoresistive random-access memory (MRAM) technology by minimal changes to the fabrication process. Such devices can be used as hardware accelerators in energy-efficient computing schemes that require a large throughput of tunably random bits.

  28. Dual-Port SOT-MRAM Achieving 90-MHz Read and 60-MHz Write Operations under Field-Assistance-Free Condition

    Masanori Natsui, Akira Tamakoshi, Hiroaki Honjo, Toshinari Watanabe, Takashi Nasuno, Chaoliang Zhang, Takaho Tanigawa, Hirofumi Inoue, Masaaki Niwa, Toru Yoshiduka, Yasuo Noguchi, Mitsuo Yasuhira, Yitao Ma, Hui Shen, Shunsuke Fukami, Hideo Sato, Shoji Ikeda, Hideo Ohno, Tetsuo Endoh, Takahiro Hanyu

    IEEE Journal of Solid-State Circuits 56 (4) 1116-1128 2021年4月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/JSSC.2020.3039800  

    ISSN:0018-9200

    eISSN:1558-173X

    詳細を見る 詳細を閉じる

    The development of new functional memories using emerging nonvolatile devices has been widely investigated. Spin-transfer torque magnetoresistive random access memory (STT-MRAM) has become new technology platform to overcome the issue in power consumption of logic for the application from IoT to AI; however, STT-MRAM has a tradeoff relationship between endurance, retention, and access time. This is because the MTJ device used in STT-MRAM is a two-terminal device, and excessive read current for high-speed readout can cause unexpected data writing, or so-called read disturbance. In order to meet the demand for the realization of high-speed nonvolatile memory, the development of new memories based on innovative circuit, device, and integration process is required. In this article, we demonstrate an SOT-MRAM, a nonvolatile memory using MTJ devices with spin-orbit-torque (SOT) switching that have a read-disturbance-free characteristic. The SOT-MRAM fabricated using a 55-nm CMOS process is implemented in a dual-port configuration utilizing a three-terminal structure of the device for realizing a wide bandwidth applicable to high-speed applications. In addition, a read-energy reduction technique called a self-termination scheme is also implemented. Through the measurement results of the fabricated prototype chip, we will demonstrate the proposed SOT-MRAM achieves 60-MHz write and 90-MHz read operations with 1.2-V supply voltage under a magnetic-field-free condition.

  29. Erratum: Coherent magnetization reversal of a cylindrical nanomagnet in shape-anisotropy magnetic tunnel junctions (Appl. Phys. Lett. (2021) 118 (082404) DOI: 10.1063/5.0043058)

    Butsurin Jinnai, Junta Igarashi, Kyota Watanabe, Eli Christopher I. Enobio, Shunsuke Fukami, Hideo Ohno

    Applied Physics Letters 118 (13) 2021年3月29日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/5.0050431  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    In the original article,1 “sin” and “cos” were mistakenly swapped in Eq. (2). The correct formof Eq. (2) should be (Formula Presented).The conversion from Fig. 4(c) to Fig. 4(d) in the original article was based on the correct form of Eq. (2), and thus, the conclusions of the paper are not affected by this erratum.

  30. Nanosecond Random Telegraph Noise in In-Plane Magnetic Tunnel Junctions

    K. Hayakawa, S. Kanai, T. Funatsu, J. Igarashi, B. Jinnai, W. A. Borders, H. Ohno, S. Fukami

    Physical Review Letters 126 (11) 2021年3月17日

    DOI: 10.1103/PhysRevLett.126.117202  

    ISSN:0031-9007

    eISSN:1079-7114

    詳細を見る 詳細を閉じる

    We study the timescale of random telegraph noise (RTN) of nanomagnets in stochastic magnetic tunnel junctions (MTJs). From analytical and numerical calculations based on the Landau-Lifshitz-Gilbert and the Fokker-Planck equations, we reveal mechanisms governing the relaxation time of perpendicular easy-axis MTJs (p-MTJs) and in-plane easy-axis MTJs (i-MTJs), showing that i-MTJs can be made to have faster RTN. Superparamagnetic i-MTJs with small in-plane anisotropy and sizable perpendicular effective anisotropy show relaxation times down to 8 ns at negligible bias current, which is more than 5 orders of magnitude shorter than that of typical stochastic p-MTJs and about 100 times faster than the shortest time of i-MTJs reported so far. The findings give a new insight and foundation in developing stochastic MTJs for high-performance probabilistic computers.

  31. Theory of relaxation time of stochastic nanomagnets

    Shun Kanai, Keisuke Hayakawa, Hideo Ohno, Shunsuke Fukami

    Physical Review B 103 (9) 2021年3月17日

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.103.094423  

    ISSN:2469-9950

    eISSN:2469-9969

    詳細を見る 詳細を閉じる

    We theoretically investigate the switching dynamics of stochastic nanomagnets and highlight the mechanism describing their relaxation time. We reveal the distinct switching mechanisms in perpendicular and in-plane easy-axis nanomagnets, and report that the relaxation time in in-plane nanomagnets varies by a few orders of magnitude only by changing the effective perpendicular anisotropy field, even though it does not contribute to the thermal stability factor. We introduce the entropy of nanomagnets into Brown's theory [Phys. Rev. 130, 1677 (1963)10.1103/PhysRev.130.1677], and reveal that the system with faster precession as well as larger damping and smaller magnetic moment shows shorter relaxation time, and explains the different time scale of relaxation times in perpendicular- and in-plane easy-axis nanomagnets. We also show that the attempt frequency changes in both perpendicular and in-plane nanomagnets depending on the magnitude of anisotropy and show that there is a lower limit of relaxation time in perpendicular systems. This work gives physical insights of thermally activated dynamics of nanomagnets as well as its material/device design guidelines for achieving shorter relaxation times.

  32. Field-free and sub-ns magnetization switching of magnetic tunnel junctions by combining spin-transfer torque and spin-orbit torque

    Chaoliang Zhang, Yutaro Takeuchi, Shunsuke Fukami, Hideo Ohno

    Applied Physics Letters 118 (9) 2021年3月1日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/5.0039061  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    We investigate the magnetization switching via a combination of spin-transfer torque (STT) and spin-orbit torque (SOT). STT and SOT are simultaneously induced by a pulsed current flowing through an in-plane easy-axis magnetic tunnel junction and an underneath Ta/W channel. SOT allows the magnetization to be switched with the sub-ns pulse down to 200 ps and STT eliminates the necessity of an external field. The switching current is much smaller than the case driven solely by STT in the short pulse regime. We also compare the threshold current between two structures having orthogonal (Type Y) and collinear (Type X) magnetic easy axes to the longitudinal direction of the channel and find that the Type X achieves smaller switching current by a factor of 1/4 at 200 ps.

  33. Coherent magnetization reversal of a cylindrical nanomagnet in shape-anisotropy magnetic tunnel junctions

    Butsurin Jinnai, Junta Igarashi, Kyota Watanabe, Eli Christopher I. Enobio, Shunsuke Fukami, Hideo Ohno

    Applied Physics Letters 118 (8) 2021年2月22日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/5.0043058  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    A shape-anisotropy magnetic tunnel junction (MTJ) holds promise for its scaling into single-digit nanometers while possessing high data-retention capability. Understanding magnetization reversal mode is crucial to quantify the thermal stability factor Δfor data retention with high accuracy. Here, we study magnetization reversal mode in the shape-anisotropy MTJ with a 15-nm-thick CoFeB layer by evaluating Δfrom two different methods: switching probability and retention time measurements. We find that magnetization reversal coherently proceeds in the 15-nm-thick and X/1X-nm-diameter cylindrical nanomagnet in the shape-anisotropy MTJs, in contrast to the conventional interfacial-anisotropy MTJs with a smaller thickness and larger diameter. The coherent magnetization reversal of the shape-anisotropy MTJ is also confirmed by astroid curve measurements. This study provides insight into the development of ultrasmall and high-reliability MTJ devices.

  34. Temperature dependence of the energy barrier in X/1X nm shape-anisotropy magnetic tunnel junctions

    Junta Igarashi, Butsurin Jinnai, Valentin Desbuis, Stéphane Mangin, Shunsuke Fukami, Hideo Ohno

    Applied Physics Letters 118 (1) 2021年1月4日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/5.0029031  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    Shape-anisotropy magnetic tunnel junctions (MTJs) are attracting much attention as a high-performance nonvolatile spintronic device in the X/1X nm regime. In this study, we investigate an energy barrier relevant to the retention property in CoFeB/MgO-based shape-anisotropy MTJs with various diameters at high temperatures and compare it with that in conventional interfacial-anisotropy MTJs. We find that the scaling relationship between the energy barrier and the spontaneous magnetization in shape-anisotropy MTJs is well described by a model assuming the dominant contribution of shape anisotropy to the energy barrier. Also, the scaling exponent is much smaller than that for the interfacial-anisotropy MTJs, indicating that the properties of shape-anisotropy MTJs are less sensitive to the temperature. Using the experimentally determined scaling relationship, we discuss the design window of the MTJ dimensions to achieve data retention of 10 years at various temperatures. This study demonstrates that the shape-anisotropy MTJ holds promise of scaling beyond 20 nm for high-temperature applications.

  35. Fast Switching Down to 3.5 ns in Sub-5-nm Magnetic Tunnel Junctions Achieved by Engineering Relaxation Time

    B. Jinnai, J. Igarashi, T. Shinoda, K. Watanabe, S. Fukami, H. Ohno

    Technical Digest - International Electron Devices Meeting, IEDM 2021-December 1-4 2021年

    DOI: 10.1109/IEDM19574.2021.9720509  

    ISSN:0163-1918

    詳細を見る 詳細を閉じる

    We show fast switching down to 3.5 ns while maintaining high data retention in sub-5-nm ultra-small magnetic tunnel junctions (MTJs) using multilayered ferromagnets (FMs). We engineer characteristic relaxation time, a critical factor for fast magnetization switching, by varying the number of CoFeB/MgO interfaces in multilayered FMs. We also find that switching efficiency improves with increasing the number of CoFeB/MgO interfaces. Harnessing the advantages of both the MTJ using multilayered FMs and shape-Anisotropy MTJ, the MTJ technology can cover a wide variety of applications even at the ultra-small scale needed for advanced-node integrated technology.

  36. High-performance shape-anisotropy magnetic tunnel junctions down to 2.3 nm

    B. Jinnai, J. Igarashi, K. Watanabe, T. Funatsu, H. Sato, S. Fukami, H. Ohno

    Technical Digest - International Electron Devices Meeting, IEDM 2020-December 24.6.1-24.6.4 2020年12月12日

    DOI: 10.1109/IEDM13553.2020.9371972  

    ISSN:0163-1918

    詳細を見る 詳細を閉じる

    We show scalability down to 2.3 nm and high performance at single-digit nanometers of shape-anisotropy magnetic tunnel junctions (MTJs) employing a multilayered ferromagnetic structure. We reveal that a free layer with two ferromagnets separated by a MgO layer behaves as a single magnet at small device dimensions owing to magnetostatic coupling in addition to exchange coupling. This nature, in turn, leads to a notable performance increase of the MTJs in the single-digit-nm regime: thermal stability factor Δ of higher than 100 at room temperature; stable switching at temperatures of 150°C or higher; and spin-transfer torque (STT) switching with a dc voltage (intrinsic critical current IC0 of 8.5 μA) and with a 10-ns pulse below 1.0 V. Also, we find that switching efficiency (Δ/IC0) increases by a factor of three or more as the size decreases. The results show that the shape-anisotropy MTJ provides a route to high-density and high-performance STT-MRAMs in the era of the ultimate scaling.

  37. Engineering Single-Shot All-Optical Switching of Ferromagnetic Materials 国際誌

    Junta Igarashi, Quentin Remy, Satoshi Iihama, Grégory Malinowski, Michel Hehn, Jon Gorchon, Julius Hohlfeld, Shunsuke Fukami, Hideo Ohno, Stéphane Mangin

    Nano Letters 20 (12) 8654-8660 2020年12月9日

    出版者・発行元:AMER CHEMICAL SOC

    DOI: 10.1021/acs.nanolett.0c03373  

    ISSN:1530-6984

    eISSN:1530-6992

    詳細を見る 詳細を閉じる

    Since it was recently demonstrated in a spin-valve structure, magnetization reversal of a ferromagnetic layer using a single ultrashort optical pulse has attracted attention for future ultrafast and energy-efficient magnetic storage or memory devices. However, the mechanism and the role of the magnetic properties of the ferromagnet as well as the time scale of the magnetization switching are not understood. Here, we investigate single-shot all-optical magnetization switching in a GdFeCo/Cu/[CoxNi1-x/Pt] spin-valve structure. We demonstrate that the threshold fluence for switching both the GdFeCo and the ferromagnetic layer depends on the laser pulse duration and the thickness and the Curie temperature of the ferromagnetic layer. We are able to explain most of the experimental results using a phenomenological model. This work provides a way to engineer ferromagnetic materials for energy efficient single-shot all-optical magnetization switching.

  38. Energy Efficient Control of Ultrafast Spin Current to Induce Single Femtosecond Pulse Switching of a Ferromagnet 国際誌

    Quentin Remy, Junta Igarashi, Satoshi Iihama, Grégory Malinowski, Michel Hehn, Jon Gorchon, Julius Hohlfeld, Shunsuke Fukami, Hideo Ohno, Stéphane Mangin

    Advanced Science 7 (23) 2001996-2001996 2020年12月2日

    出版者・発行元:WILEY

    DOI: 10.1002/advs.202001996  

    eISSN:2198-3844

    詳細を見る 詳細を閉じる

    New methods to induce magnetization switching in a thin ferromagnetic material using femtosecond laser pulses without the assistance of an applied external magnetic field have recently attracted a lot of interest. It has been shown that by optically triggering the reversal of the magnetization in a GdFeCo layer, the magnetization of a nearby ferromagnetic thin film can also be reversed via spin currents originating in the GdFeCo layer. Here, using a similar structure, it is shown that the magnetization reversal of the GdFeCo is not required in order to reverse the magnetization of the ferromagnetic thin film. This switching is attributed to the ultrafast spin current and can be generated by the GdFeCo demagnetization. A larger energy efficiency of the ferromagnetic layer single pulse switching is obtained for a GdFeCo with a larger Gd concentration. Those ultrafast and energy efficient switchings observed in such spintronic devices open a new path toward ultrafast and energy efficient magnetic memories.

  39. Spin-orbit torque switching of an antiferromagnetic metallic heterostructure

    Samik DuttaGupta, A. Kurenkov, Oleg A. Tretiakov, G. Krishnaswamy, G. Sala, V. Krizakova, F. Maccherozzi, S. S. Dhesi, P. Gambardella, S. Fukami, H. Ohno

    Nature Communications 11 (1) 2020年12月

    DOI: 10.1038/s41467-020-19511-4  

    eISSN:2041-1723

    詳細を見る 詳細を閉じる

    The ability to represent information using an antiferromagnetic material is attractive for future antiferromagnetic spintronic devices. Previous studies have focussed on the utilization of antiferromagnetic materials with biaxial magnetic anisotropy for electrical manipulation. A practical realization of these antiferromagnetic devices is limited by the requirement of material-specific constraints. Here, we demonstrate current-induced switching in a polycrystalline PtMn/Pt metallic heterostructure. A comparison of electrical transport measurements in PtMn with and without the Pt layer, corroborated by x-ray imaging, reveals reversible switching of the thermally-stable antiferromagnetic Néel vector by spin-orbit torques. The presented results demonstrate the potential of polycrystalline metals for antiferromagnetic spintronics.

  40. Giant voltage-controlled modulation of spin Hall nano-oscillator damping 国際誌

    Himanshu Fulara, Mohammad Zahedinejad, Roman Khymyn, Mykola Dvornik, Shunsuke Fukami, Shun Kanai, Hideo Ohno, Johan Åkerman

    Nature Communications 11 (1) 4006-4006 2020年12月1日

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/s41467-020-17833-x  

    ISSN:2041-1723

    eISSN:2041-1723

    詳細を見る 詳細を閉じる

    Spin Hall nano-oscillators (SHNOs) are emerging spintronic devices for microwave signal generation and oscillator-based neuromorphic computing combining nano-scale footprint, fast and ultra-wide microwave frequency tunability, CMOS compatibility, and strong non-linear properties providing robust large-scale mutual synchronization in chains and two-dimensional arrays. While SHNOs can be tuned via magnetic fields and the drive current, neither approach is conducive to individual SHNO control in large arrays. Here, we demonstrate electrically gated W/CoFeB/MgO nano-constrictions in which the voltage-dependent perpendicular magnetic anisotropy tunes the frequency and, thanks to nano-constriction geometry, drastically modifies the spin-wave localization in the constriction region resulting in a giant 42% variation of the effective damping over four volts. As a consequence, the SHNO threshold current can be strongly tuned. Our demonstration adds key functionality to nano-constriction SHNOs and paves the way for energy-efficient control of individual oscillators in SHNO chains and arrays for neuromorphic computing.

  41. Probing edge condition of nanoscale CoFeB/MgO magnetic tunnel junctions by spin-wave resonance

    M. Shinozaki, T. Dohi, J. Igarashi, J. Llandro, S. Fukami, H. Sato, H. Ohno

    Applied Physics Letters 117 (20) 2020年11月16日

    DOI: 10.1063/5.0020591  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    We investigate spin-wave resonance in nanoscale CoFeB/MgO magnetic tunnel junctions (MTJs) with a perpendicular easy axis and various free-layer sizes. Two types of MTJs are fabricated by different process conditions, and the spin-wave resonance is measured with homodyne-detected ferromagnetic resonance. We focus on the distance between resonance frequencies of the uniform and spin-wave modes as a function of the free-layer size in order to examine the effect of the edge state of MTJs. A marked difference is observed between the two types of MTJs, and the result is consistently reproduced by a model assuming free-or fixed-edge boundary conditions with or without reduced magnetic properties near the pattern edge for each MTJ. The obtained results indicate that the edge state of nanoscale MTJs is crucially affected by the process condition, and spin-wave resonance can serve as a sensitive probe for the edge condition.

  42. Multidomain Memristive Switching of Pt38Mn62/ [Co/Ni] n Multilayers

    G. K. Krishnaswamy, A. Kurenkov, G. Sala, M. Baumgartner, V. Krizakova, C. Nistor, F. MacCherozzi, S. S. Dhesi, S. Fukami, H. Ohno, P. Gambardella

    Physical Review Applied 14 (4) 2020年10月20日

    DOI: 10.1103/PhysRevApplied.14.044036  

    eISSN:2331-7019

    詳細を見る 詳細を閉じる

    We investigate the mechanism of analoglike switching of Pt38Mn62/[Co/Ni] multilayers induced by spin-orbit torques. X-ray photoemission microscopy performed during magnetization reversal driven by current pulses shows that sequential switching of reproducible domain patterns can be achieved. Switching proceeds by domain-wall displacement starting from the edges of blocked ferromagnetic domains, which do not switch for either direction of the current and represent up to 24% of the total ferromagnetic area. The antiferromagnetic Pt38Mn62 layer has a granular texture, with the majority of the domains being smaller than 100 nm, whereas the ferromagnetic domains in Co/Ni are typically larger than 200 nm. The blocked domains and the granular distribution of exchange bias constrain the origin as well as the displacement of the domain walls, thus leading to highly reproducible switching patterns as a function of the applied current pulses. These measurements clarify the origin of the memristive behavior in antiferromagnet-ferromagnet structures and provide clues for further optimization of spin-orbit torque switching and memristivity in these systems.

  43. All-optical probe of magnetization precession modulated by spin-orbit torque

    Kazuaki Ishibashi, Satoshi Iihama, Yutaro Takeuchi, Kaito Furuya, Shun Kanai, Shunsuke Fukami, Shigemi Mizukami

    Applied Physics Letters 117 (12) 2020年9月21日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/5.0020852  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    Laser-induced magnetization precession modulated by an in-plane direct current was investigated in a W/CoFeB/MgO micron-sized strip using an all-optical time-resolved magneto-optical Kerr effect microscope. We observed a relatively large change in the precession frequency, owing to a current-induced spin-orbit torque. The generation efficiency of the spin-orbit torque was evaluated as-0.35 ± 0.03, which was in accordance with that evaluated from the modulation of damping. This technique may become an alternate method for the evaluation of spin-orbit torque.

  44. Antiferromagnetic spintronics

    Shunsuke Fukami, Virginia O. Lorenz, Olena Gomonay

    Journal of Applied Physics 128 (7) 2020年8月21日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/5.0023614  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    The ‘Antiferromagnetic Spintronics’ Special Topic in the Journal of Applied Physics offers an overview of the most active research areas under investigation in the broad field of antiferromagnetic spintronics. In particular, featured topics include fundamental magnetic properties, spin transport, switching, and domain wall or skyrmion motion of collinear and non-collinear anti ferromagnets, as well as growth and characterization techniques. A variety of theoretical and experimental works on fundamental magnetic properties of various antiferromagnetic materials are reported. Special attention is given to the investigation of the magnetic anisotropy profiles, the detailed structure of these are extremely important for the effective control of antiferromagnetic states.

  45. Neuromorphic computing with antiferromagnetic spintronics

    Aleksandr Kurenkov, Shunsuke Fukami, Hideo Ohno

    Journal of Applied Physics 128 (1) 2020年7月7日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/5.0009482  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    While artificial intelligence, capable of readily addressing cognitive tasks, has transformed technologies and daily lives, there remains a huge gap with biological systems in terms of performance per energy unit. Neuromorphic computing, in which hardware with alternative architectures, circuits, devices, and/or materials is explored, is expected to reduce the gap. Antiferromagnetic spintronics could offer a promising platform for this scheme. Active functionalities of antiferromagnetic systems have been demonstrated recently and several works indicated their potential for biologically inspired computing. In this perspective, we look through the prism of these works and discuss prospects and challenges of antiferromagnetic spintronics for neuromorphic computing. Overview and discussion are given on non-spiking artificial neural networks, spiking neural networks, and reservoir computing.

  46. Composition dependence of spin-orbit torque in Pt<inf>1-</inf><inf>x </inf>Mn<inf>x </inf>/CoFeB heterostructures 査読有り

    K. Vihanga De Zoysa, Samik Duttagupta, Ryuichi Itoh, Yutaro Takeuchi, Hideo Ohno, Shunsuke Fukami

    Applied Physics Letters 117 (1) 012402-012402 2020年7月6日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/5.0011448  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    We investigate spin-orbit torques (SOTs) in heterostructures with Pt1-xMnx alloy and CoFeB as a function of Mn composition (x) by using an extended harmonic Hall measurement. Slonczewski-like and field-like SOT efficiencies (ζ SL and ζ FL) show non-monotonic variation and a different trend with respect to x, and considerably large ζ SL up to 0.21 is obtained at x = 0.20. Compared to the x dependence of longitudinal resistivity, the Slonczewski-like SOT in the low x region is mainly attributed to an intrinsic spin-Hall mechanism, whereas a non-monotonic variation in the higher x region suggests the presence of additional factors. The present findings deliver useful clues to understand the physics behind SOT generation in antiferromagnetic heterostructures and offer a route to realize efficient devices.

  47. Current distribution in metallic multilayers from resistance measurements

    Ondřej Stejskal, André Thiaville, Jaroslav Hamrle, Shunsuke Fukami, Hideo Ohno

    Physical Review B 101 (23) 2020年6月15日

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.101.235437  

    ISSN:2469-9950

    eISSN:2469-9969

    詳細を見る 詳細を閉じる

    The in-plane current profile within multilayers of the generic structure Ta/Pt/(CoNi)/Pt/Ta is investigated. A large set of samples where the thickness of each layer was systematically varied was grown, followed by the measurement of the sheet resistance of each sample. The data are analyzed by a series of increasingly elaborate models, from a macroscopic engineering approach to mesoscopic transport theory. Non-negligible variations of the estimated repartition of current between the layers are found. The importance of having additional structural data is highlighted.

  48. Dual-Port Field-Free SOT-MRAM Achieving 90-MHz Read and 60-MHz Write Operations under 55-nm CMOS Technology and 1.2-V Supply Voltage

    M. Natsui, A. Tamakoshi, H. Honjo, T. Watanabe, T. Nasuno, C. Zhang, T. Tanigawa, H. Inoue, M. Niwa, T. Yoshiduka, Y. Noguchi, M. Yasuhira, Y. Ma, H. Shen, S. Fukami, H. Sato, S. Ikeda, H. Ohno, T. Endoh, T. Hanyu

    IEEE Symposium on VLSI Circuits, Digest of Technical Papers 2020-June 2020年6月

    DOI: 10.1109/VLSICircuits18222.2020.9162774  

    詳細を見る 詳細を閉じる

    We demonstrate an SOT-MRAM, a nonvolatile memory using spin-orbit-torque (SOT) devices that have a read-disturbance-free characteristic. The SOT-MRAM fabricated by a 55-nm CMOS process achieves 60-MHz write and 90-MHz read operations with 1.2-V supply voltage under a magnetic-field-free condition. The SOT-MRAM is also implemented in a dual-port configuration utilizing three-terminal structure of the device, which realizes a wide bandwidth applicable to high-speed applications.

  49. Probabilistic computing based on spintronics technology

    Shunsuke Fukami, William A. Borders, Ahmed Z. Pervaiz, Kerem Y. Camsari, Supriyo Datta, Hideo Ohno

    2020 IEEE Silicon Nanoelectronics Workshop, SNW 2020 21-22 2020年6月

    出版者・発行元:IEEE

    DOI: 10.1109/SNW50361.2020.9131622  

    ISSN:2161-4636

    詳細を見る 詳細を閉じる

    There have been increasing demands on realizing computing hardware capable of addressing complex tasks that classical von-Neumann computers cannot readily execute. Here we show an unconventional computing scheme-probabilistic computing-based on a spintronics technology, which is promising to address various computationally hard problems. We present a proof-of-concept of the probabilistic computer with stochastic magnetic tunnel junctions, that can perform optimization problems at room temperature.

  50. Visualizing magnetic structure in 3d nanoscale ni-fe gyroid networks 国際誌 査読有り

    Justin Llandro, David M. Love, András Kovács, Jan Caron, Kunal N. Vyas, Attila Kákay, Ruslan Salikhov, Kilian Lenz, Jürgen Fassbender, Maik R.J. Scherer, Christian Cimorra, Ullrich Steiner, Crispin H.W. Barnes, Rafal E. Dunin-Borkowski, Shunsuke Fukami, Hideo Ohno

    Nano Letters 20 (5) 3642-3650 2020年5月13日

    出版者・発行元:AMER CHEMICAL SOC

    DOI: 10.1021/acs.nanolett.0c00578  

    ISSN:1530-6984

    eISSN:1530-6992

    詳細を見る 詳細を閉じる

    Arrays of interacting 2D nanomagnets display unprecedented electromagnetic properties via collective effects, demonstrated in artificial spin ices and magnonic crystals. Progress toward 3D magnetic metamaterials is hampered by two challenges: fabricating 3D structures near intrinsic magnetic length scales (sub-100 nm) and visualizing their magnetic configurations. Here, we fabricate and measure nanoscale magnetic gyroids, periodic chiral networks comprising nanowire-like struts forming three-connected vertices. Via block copolymer templating, we produce Ni Fe single-gyroid and double-gyroid (an inversion pair of single-gyroids) nanostructures with a 42 nm unit cell and 11 nm diameter struts, comparable to the exchange length in Ni-Fe. We visualize their magnetization distributions via off-axis electron holography with nanometer spatial resolution and interpret the patterns using finite-element micromagnetic simulations. Our results suggest an intricate, frustrated remanent state which is ferromagnetic but without a unique equilibrium configuration, opening new possibilities for collective phenomena in magnetism, including 3D magnonic crystals and unconventional computing. 75 25

  51. Scaling magnetic tunnel junction down to single-digit nanometers - Challenges and prospects 査読有り

    Butsurin Jinnai, Kyota Watanabe, Shunsuke Fukami, Hideo Ohno

    Applied Physics Letters 116 (16) 160501-160501 2020年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/5.0004434  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    Magnetic tunnel junction (MTJ), a spintronics device, has been intensively developed in the past couple of decades because of its high potential in terms of non-volatility, fast operation, virtually infinite endurance, scalability, and compatibility with complementary metal-oxide-semiconductor (CMOS) integrated circuits as well as their process and circuits. Today, high-volume manufacturing of spin-transfer torque magnetoresistive random access memory based on MTJ has been initiated for embedded memory applications in CMOS logic. Whether MTJ is scalable along with the advancement of CMOS technology is critical for the technology's future. Here, we review the scaling of MTJ technology, from in-plane anisotropy MTJs to perpendicular interfacial- or shape-anisotropy MTJs. We also discuss challenges and prospects in the future 1X- and X-nm era.

  52. スピントロニクスデバイスに基づくシナプスの数理モデル

    佐藤 拓, 菊地優志, Aleksandr Kurenkov, 堀尾喜彦, 深見俊輔

    電子情報通信学会技術報告 NLP2019-122 55-60 2020年3月

  53. Crystal orientation and anomalous Hall effect of sputter-deposited non-collinear antiferromagnetic Mn<inf>3</inf>Sn thin films

    Juyoung Yoon, Yutaro Takeuchi, Ryuichi Itoh, Shun Kanai, Shunsuke Fukami, Hideo Ohno

    Applied Physics Express 13 (1) 2020年1月1日

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/1882-0786/ab5874  

    ISSN:1882-0778

    eISSN:1882-0786

    詳細を見る 詳細を閉じる

    We study a growth technique of non-collinear antiferromagnetic Mn Sn thin films deposited by sputtering with various substrates and underlayers. The relation between their crystal structure and magnetic/transport properties is also investigated. We achieve the formation of epitaxial films with both C-plane and M-plane orientations, whose Kagome lattices are parallel and perpendicular to the plane, respectively. Transverse resistivity originating from the anomalous Hall effect shows different trends reflecting the Kagome lattice orientation of each stack. The established technique and findings offer a platform to study functional devices utilizing the unconventional physical properties of non-collinear antiferromagnets with controlled Kagome lattice orientation. 3

  54. 熱ダイナミクスを利用したスピントロニクスニューロンデバイスの数理モデル

    菊地 優志, 佐藤 拓, Aleksandr KURENKOV, 堀尾 喜彦, 深見 俊輔

    電子情報通信学会技術報告 NLP2019-104 96-104 2020年1月

  55. Stack structure and temperature dependence of spin-orbit torques in heterostructures with antiferromagnetic PtMn

    Ryuichi Itoh, Yutaro Takeuchi, Samik Duttagupta, Shunsuke Fukami, Hideo Ohno

    Applied Physics Letters 115 (24) 2019年12月9日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.5129829  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    We evaluate the stack structure and temperature dependence of the spin-orbit torques (SOTs) in metallic antiferromagnet (AFM)/ferromagnet (FM) PtMn/CoFeB heterostructures using an extended harmonic Hall measurement. We show that PtMn/CoFeB exhibits sizable Slonczewski-like and fieldlike SOTs whose magnitude is comparable to that of heterostructures with nonmagnetic heavy metals like Pt or Ta. We also find that the SOTs in our PtMn/CoFeB structures are virtually constant with temperature. The findings will offer clues to understand the generation mechanism of SOTs in AFM/FM systems and pave the way for nonvolatile memory and neuromorphic computing applications.

  56. ブレインモルフィックコンピューティングハードウェアへのスピントロニクス素子の応用 招待有り

    堀尾喜彦, 深見俊輔

    応用物理学会 応用電子物性分科会誌 25 (5) 167-172 2019年12月

  57. Spin-orbit torque neuron and synapse devices for brainmorphic computing 査読有り

    堀尾喜彦, Aleksandr Kurenkov, 深見俊輔, 大野英男

    Proceedings of International Symposium on Nonlinear Theory and Its Applications 78-78 2019年12月

  58. First demonstration of field-free SOT-MRAM with 0.35 ns write speed and 70 thermal stability under 400℃ thermal tolerance by canted SOT structure and its advanced patterning/SOT channel technology 査読有り

    International Electron Device Meeting 2019-December 2019年12月

    DOI: 10.1109/IEDM19573.2019.8993443  

    ISSN:0163-1918

  59. Formation and current-induced motion of synthetic antiferromagnetic skyrmion bubbles 国際誌 査読有り

    Takaaki Dohi, Samik DuttaGupta, Shunsuke Fukami, Hideo Ohno

    Nature Communications 10 (1) 5153-5153 2019年12月1日

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/s41467-019-13182-6  

    ISSN:2041-1723

    eISSN:2041-1723

    詳細を見る 詳細を閉じる

    Skyrmion, a topologically-protected soliton, is known to emerge via electron spin in various magnetic materials. The magnetic skyrmion can be driven by low current density and has a potential to be stabilized in nanoscale, offering new directions of spintronics. However, there remain some fundamental issues in widely-studied ferromagnetic systems, which include a difficulty to realize stable ultrasmall skyrmions at room temperature, presence of the skyrmion Hall effect, and limitation of velocity owing to the topological charge. Here we show skyrmion bubbles in a synthetic antiferromagnetic coupled multilayer that are free from the above issues. Additive Dzyaloshinskii-Moriya interaction and spin-orbit torque (SOT) of the tailored stack allow stable skyrmion bubbles at room temperature, significantly smaller threshold current density or higher speed for motion, and negligible skyrmion Hall effect, with a potential to be scaled down to nanometer dimensions. The results offer a promising pathway toward nanoscale and energy-efficient skyrmion-based devices.

  60. Giant perpendicular magnetic anisotropy in Ir/Co/Pt multilayers 査読有り

    Yong Chang Lau, Zhendong Chi, Tomohiro Taniguchi, Masashi Kawaguchi, Goro Shibata, Naomi Kawamura, Motohiro Suzuki, Shunsuke Fukami, Atsushi Fujimori, Hideo Ohno, Masamitsu Hayashi

    Physical Review Materials 3 (10) 2019年10月25日

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevMaterials.3.104419  

    ISSN:2475-9953

    eISSN:2475-9953

    詳細を見る 詳細を閉じる

    We have studied the magnetic properties of multilayers composed of ferromagnetic metal Co and heavy metals with strong spin orbit coupling (Pt and Ir). Multilayers with symmetric (ABA stacking) and asymmetric (ABC stacking) structures are grown to study the effect of broken structural inversion symmetry. We compare the perpendicular magnetic anisotropy (PMA) energy of symmetric Pt/Co/Pt, Ir/Co/Ir multilayers and asymmetric Pt/Co/Ir, Ir/Co/Pt multilayers. First, the interface contribution to the PMA is studied using the Co layer thickness dependence of the effective PMA energy. Comparison of the interfacial PMA between the Ir/Co/Pt, Pt/Co/Ir asymmetric structures and Pt/Co/Pt, Ir/Co/Ir symmetric structures indicate that the broken structural inversion symmetry induced PMA is small compared to the overall interfacial PMA. Second, we find the magnetic anisotropy field is significantly increased in multilayers when the ferromagnetic layers are antiferromagnetically coupled via interlayer exchange coupling (IEC). Macrospin model calculations can qualitatively account for the relation between the anisotropy field and the IEC. Among the structures studied, the IEC is the largest for the asymmetric Ir/Co/Pt multilayers: the exchange coupling field exceeds 3 T and consequently, the anisotropy field approaches 10 T. Third, comparing the asymmetric Ir/Co/Pt and Pt/Co/Ir structures, we find the IEC and, to some extent, the interface PMA are stronger for the former than the latter. X-ray magnetic circular dichroism (XMCD) studies suggest that the proximity-induced magnetization in Pt is larger for the Ir/Co/Pt multilayers than the inverted structure (Pt/Co/Ir), which may partly account for the difference in the magnetic properties. These results show the intricate relation between PMA, IEC, and the proximity-induced magnetization that can be exploited to design artificial structures with unique magnetic characteristics.

  61. Write-error rate of nanoscale magnetic tunnel junctions in the precessional regime 査読有り

    Takaharu Saino, Shun Kanai, Motoya Shinozaki, Butsurin Jinnai, Hideo Sato, Shunsuke Fukami, Hideo Ohno

    Applied Physics Letters 115 (14) 2019年9月30日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.5121157  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    We investigate the write-error rate (WER) of spin-transfer torque (STT)-induced switching in nanoscale magnetic tunnel junctions (MTJs) for various pulse durations down to 3 ns. While the pulse duration dependence of switching current density shows a typical behavior of the precessional regime, WER vs current density is not described by an analytical solution known for the precessional regime. The measurement of WER as a function of magnetic field suggests that the WER is characterized by an effective damping constant, which is significantly larger than the value determined by ferromagnetic resonance. The current density dependence of WER is well reproduced by a macrospin model with thermal fluctuation using the effective damping constant. The obtained finding implies a larger relaxation rate and/or thermal agitation during STT switching, offering a previously unknown insight toward high-reliability memory applications.

  62. Integer factorization using stochastic magnetic tunnel junctions 国際誌 査読有り

    William A. Borders, Ahmed Z. Pervaiz, Shunsuke Fukami, Kerem Y. Camsari, Hideo Ohno, Supriyo Datta

    Nature 573 (7774) 390-393 2019年9月19日

    出版者・発行元:NATURE RESEARCH

    DOI: 10.1038/s41586-019-1557-9  

    ISSN:0028-0836

    eISSN:1476-4687

    詳細を見る 詳細を閉じる

    Conventional computers operate deterministically using strings of zeros and ones called bits to represent information in binary code. Despite the evolution of conventional computers into sophisticated machines, there are many classes of problems that they cannot efficiently address, including inference, invertible logic, sampling and optimization, leading to considerable interest in alternative computing schemes. Quantum computing, which uses qubits to represent a superposition of 0 and 1, is expected to perform these tasks efficiently . However, decoherence and the current requirement for cryogenic operation , as well as the limited many-body interactions that can be implemented, pose considerable challenges. Probabilistic computing is another unconventional computation scheme that shares similar concepts with quantum computing but is not limited by the above challenges. The key role is played by a probabilistic bit (a p-bit)—a robust, classical entity fluctuating in time between 0 and 1, which interacts with other p-bits in the same system using principles inspired by neural networks . Here we present a proof-of-concept experiment for probabilistic computing using spintronics technology, and demonstrate integer factorization, an illustrative example of the optimization class of problems addressed by adiabatic and gated quantum computing. Nanoscale magnetic tunnel junctions showing stochastic behaviour are developed by modifying market-ready magnetoresistive random-access memory technology and are used to implement three-terminal p-bits that operate at room temperature. The p-bits are electrically connected to form a functional asynchronous network, to which a modified adiabatic quantum computing algorithm that implements three- and four-body interactions is applied. Factorization of integers up to 945 is demonstrated with this rudimentary asynchronous probabilistic computer using eight correlated p-bits, and the results show good agreement with theoretical predictions, thus providing a potentially scalable hardware approach to the difficult problems of optimization and sampling. 1–3 4 1,5–7 8 9 2 10,11

  63. Spin-Pumping-Free Determination of Spin-Orbit Torque Efficiency from Spin-Torque Ferromagnetic Resonance

    Atsushi Okada, Yutaro Takeuchi, Kaito Furuya, Chaoliang Zhang, Hideo Sato, Shunsuke Fukami, Hideo Ohno

    Physical Review Applied 12 (1) 2019年7月23日

    DOI: 10.1103/PhysRevApplied.12.014040  

    eISSN:2331-7019

    詳細を見る 詳細を閉じる

    Spin-torque ferromagnetic resonance (ST-FMR) provides a useful tool to investigate various magnetic properties in spintronic systems, where one excites FMR by applying a rf current and detects the dc voltage generated through rectification effects. While this scheme has been used to characterize spin-orbit torques (SOTs) that have attracted much attention recently, it is known that dc voltages can also be generated by spin pumping that overlaps with the signal from the rectification effects. Here, we show a method to determine the SOT generation efficiency by ST-FMR free from spin pumping using two representative material systems, W/Co-Fe-B/MgO and Pt/Co/MgO. In addition, using the values determined by the method, which are confirmed to agree well with the results of a separately performed extended harmonic Hall measurement, we also quantify the amount of overestimation if the results obtained by a conventional ST-FMR setup are analyzed without considering the spin pumping. The present finding offers a useful insight to obtain a reliable value of SOT efficiency using ST-FMR, in particular for systems that exhibit large SOT, which accompanies large spin pumping.

  64. Artificial Neuron and Synapse Realized in an Antiferromagnet/Ferromagnet Heterostructure Using Dynamics of Spin–Orbit Torque Switching 国際誌 査読有り

    Aleksandr Kurenkov, Samik DuttaGupta, Chaoliang Zhang, Shunsuke Fukami, Yoshihiko Horio, Hideo Ohno

    Advanced Materials 31 (23) e1900636 2019年6月6日

    出版者・発行元:WILEY-V C H VERLAG GMBH

    DOI: 10.1002/adma.201900636  

    ISSN:0935-9648

    eISSN:1521-4095

    詳細を見る 詳細を閉じる

    Efficient information processing in the human brain is achieved by dynamics of neurons and synapses, motivating effective implementation of artificial spiking neural networks. Here, the dynamics of spin–orbit torque switching in antiferromagnet/ferromagnet heterostructures is studied to show the capability of the material system to form artificial neurons and synapses for asynchronous spiking neural networks. The magnetization switching, driven by a single current pulse or trains of pulses, is examined as a function of the pulse width (1 s to 1 ns), amplitude, number, and pulse-to-pulse interval. Based on this dynamics and the unique ability of the system to exhibit binary or analog behavior depending on the device size, key functionalities of a synapse (spike-timing-dependent plasticity) and a neuron (leaky integrate-and-fire) are reproduced in the same material and on the basis of the same working principle. These results open a way toward spintronics-based neuromorphic hardware that executes cognitive tasks with the efficiency of the human brain.

  65. Artificial neuron and synapse realized in an antiferromagnet/ferromagnet heterostructure using dynamics of spin-orbit torque switching 査読有り

    A. Kurenkov, S. DuttaGupta, C. Zhang, S. Fukami, Y. Horio, H. Ohno

    Advanced Materials 31 (23) 1900636 2019年4月

    DOI: 10.1002/adma.201900636  

  66. Reversal of domain wall chirality with ferromagnet thickness in W/(Co)FeB/MgO systems 査読有り

    Takaaki Dohi, Samik Duttagupta, Shunsuke Fukami, Hideo Ohno

    Applied Physics Letters 114 (4) 042405 2019年1月28日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.5084095  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    We investigate the effect of the Dzyaloshinskii-Moriya interaction (DMI) on domain wall (DW) configurations in W/(Co)FeB/MgO structures with varying ferromagnet (FM) thicknesses. The DW chirality and effective DMI field are evaluated from field-induced DW motion. The results indicate a reversal of DW chirality with the FM thickness irrespective of the FM material (CoFeB or FeB) and the crystallographic phase of W (α or β phase). The observed change in the magnitude of the DMI field is supported by an additional measurement of spin-orbit torque assisted magnetization switching under in-plane magnetic fields. The present findings offer previously unknown insights into the origin of interfacial DMI and indicate the co-existence of multiple factors governing DW chirality in systems with broken inversion symmetry.

  67. Spin-orbit torque-induced switching of in-plane magnetized elliptic nanodot arrays with various easy-axis directions measured by differential planar Hall resistance 査読有り

    Yu Takahashi, Yutaro Takeuchi, Chaoliang Zhang, Butsurin Jinnai, Shunsuke Fukami, Hideo Ohno

    Applied Physics Letters 114 (1) 012410 2019年1月7日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.5075542  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    Spin-orbit torque-induced switching of an elliptical nanomagnet with an in-plane easy axis allows sub-ns and field-free operation. Since its properties crucially depend on the design of the nanomagnet such as the easy-axis direction, it is of high importance to systematically elucidate the dependence of performance on various parameters of the nanomagnet towards magnetoresistive random access memory applications. Here, we show a scheme to statistically evaluate the switching properties of in-plane nanomagnets in a short turnaround time. We use devices with an array of CoFeB/MgO nanomagnets formed on a cross-shaped Ta/W Hall bar, and the differential planar Hall resistance is measured to study the magnetization switching. Using the scheme, we investigate the easy-axis angle dependence of switching properties at zero magnetic fields for various current pulse widths from 100 ms to 1.7 ns. We show that the dependence of threshold switching current on the easy-axis direction significantly varies with the pulse width.

  68. Shape anisotropy revisited in single-digit nanometer magnetic tunnel junctions 査読有り

    K. Watanabe, B. Jinnai, S. Fukami, H. Sato, H. Ohno

    Nature Communications 9 (1) 2018年12月1日

    出版者・発行元:Nature Publishing Group

    DOI: 10.1038/s41467-018-03003-7  

    ISSN:2041-1723

    eISSN:2041-1723

    詳細を見る 詳細を閉じる

    Nanoscale magnetic tunnel junctions play a pivotal role in magnetoresistive random access memories. Successful implementation depends on a simultaneous achievement of low switching current for the magnetization switching by spin transfer torque and high thermal stability, along with a continuous reduction of junction size. Perpendicular easy-axis CoFeB/MgO stacks possessing interfacial anisotropy have paved the way down to 20-nm scale, below which a new approach needs to be explored. Here we show magnetic tunnel junctions that satisfy the requirements at ultrafine scale by revisiting shape anisotropy, which is a classical part of magnetic anisotropy but has not been fully utilized in the current perpendicular systems. Magnetization switching solely driven by current is achieved for junctions smaller than 10 nm where sufficient thermal stability is provided by shape anisotropy without adopting new material systems. This work is expected to push forward the development of magnetic tunnel junctions toward single-digit nm-scale nano-magnetics/spintronics.

  69. Scalability and wide temperature range operation of spin-orbit torque switching devices using Co/Pt multilayer nanowires 査読有り

    Butsurin Jinnai, Hideo Sato, Shunsuke Fukami, Hideo Ohno

    Applied Physics Letters 113 (21) 212403 2018年11月19日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.5045814  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    Spin-orbit torque (SOT) switching and retention properties in Co/Pt multilayer nanowire structures with various widths w down to 20 nm and the temperature dependences of the performance in the nanowire device with w = 20 nm are studied. Switching current I scales down as w is reduced. The nanowire devices show high thermal stability factor Δ > 100 for all the widths at room temperature. In the 20-nm-wide device, while a magnetization can be switched by current from -50 to 125 °C with a marginal increase in I as the temperature decreases, Δ of more than 100 is kept up to 125 °C. These results indicate that SOT-switching devices using Co/Pt multilayers are scalable in nanoscale dimensions and can operate over a wide range of temperatures, offering high potential for a wide variety of applications including automobile and aerospace. sw sw

  70. Angle dependent magnetoresistance in heterostructures with antiferromagnetic and non-magnetic metals 査読有り

    S. Duttagupta, R. Itoh, S. Fukami, H. Ohno

    Applied Physics Letters 113 (20) 202404 2018年11月12日

    DOI: 10.1063/1.5049566  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    We report on the magnetoresistive effects in a metallic antiferromagnet (AFM)/nonmagnet (NM) PtMn/Pt heterostructure with varying thickness of PtMn (1 nm ≤ t ≤ 10 nm). Longitudinal magnetoresistive effects are measured for magnetic field rotations along three mutually perpendicular directions. The results show a transformation in the functional dependencies with the increase in t and are attributed to the spin Hall magnetoresistive effects arising from the interaction of spin currents generated by Pt with the antiferromagnetic PtMn. The present findings with appreciable magnetoresistive effects in an AFM/NM metallic heterostructure add yet another option of the material system for antiferromagnetic spintronics. PtMn PtMn

  71. An effect of capping-layer material on interfacial anisotropy and thermal stability factor of MgO/CoFeB/Ta/CoFeB/MgO/capping-layer structure 査読有り

    M. Bersweiler, E. C.I. Enobio, S. Fukami, H. Sato, H. Ohno

    Applied Physics Letters 113 (17) 172401 2018年10月22日

    DOI: 10.1063/1.5050486  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    We investigate the magnetic properties of a MgO/CoFeB/Ta/CoFeB/MgO/capping-layer (Ru or Ta) structure and properties of a magnetic tunnel junction with the structure as a free layer. By using Ru instead of Ta as the capping layer, interfacial anisotropy K increases by a factor of ∼2 and a smaller damping constant is obtained. The increase in K results in an enhancement of the thermal stability factor of the free layer with the Ru capping layer compared with that with the Ta capping layer in magnetic tunnel junctions. i i

  72. Perspective: Spintronic synapse for artificial neural network 招待有り 査読有り

    Shunsuke Fukami, Hideo Ohno

    Journal of Applied Physics 124 (15) 151904 2018年10月21日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.5042317  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    While digital integrated circuits with von Neumann architectures, having exponentially evolved for half a century, are an indispensable building block of today's information society, recently growing demand on executing more complex tasks like the human brain has allowed a revisit to the architecture of information processing. Brain-inspired hardware using artificial neural networks is expected to offer a complementary approach to deal with complex problems. Since the neuron and synapse are key components of brains, most of the mathematical models of artificial neural networks require artificial neurons and synapses. Consequently, much effort has been devoted to creating artificial neurons and synapses using various solid-state systems with ferroelectric materials, phase-change materials, oxide-based memristive materials, and so on. Here, we review an example of studies on an artificial synapse based on spintronics and its application to artificial neural networks. The spintronic synapse, having analog and nonvolatile memory functionality, consists of an antiferromagnet/ferromagnet heterostructure and is operated by spin-orbit torque. After giving an overview of this field, we describe the operation principle and results of analog magnetization switching of the spintronic synapse. We then review a proof-of-concept demonstration of the artificial neural network with 36 spintronic synapses, where an associative memory operation based on the Hopfield model is performed and the learning ability of the spintronic synapses is confirmed, showing promise for low-power neuromorphic computation.

  73. Characterization of spin–orbit torque-controlled synapse device for artificial neural network applications 査読有り

    W. A. Borders, S. Fukami, H. Ohno

    Japanese Journal of Applied Physics 57 (10) 1002B2 2018年10月

    出版者・発行元:None

    DOI: 10.7567/JJAP.57.1002B2  

    ISSN:0021-4922

    eISSN:1347-4065

  74. Non-linear variation of domain period under electric field in demagnetized CoFeB/MgO stacks with perpendicular easy axis 査読有り

    N. Ichikawa, T. Dohi, A. Okada, H. Sato, S. Fukami, H. Ohno

    Applied Physics Letters 112 (20) 2018年5月14日

    出版者・発行元:American Institute of Physics Inc.

    DOI: 10.1063/1.5035487  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    We investigate a variation of magnetic domain pattern in demagnetized perpendicular-easy-axis CoFeB/MgO stacks with a wide-range electric field and discuss the electric-field effect on the exchange stiffness constant A . We observe a non-linear variation of domain period D with the applied electric field, in contrast to the effective perpendicular anisotropy field H that is evaluated from a ferromagnetic resonance and shows a linear response. An analysis based on a model describing the relation of D to A and H suggests that A varies non-linearly with the electric field, implying an involved characteristic mechanism of the exchange stiffness in the studied systems. A possible scenario for explaining the non-linear behavior of A is discussed. S P K P S K S S eff eff

  75. Spin-orbit torques in high-resistivity-W/CoFeB/MgO 査読有り

    Yutaro Takeuchi, Chaoliang Zhang, Atsushi Okada, Hideo Sato, Shunsuke Fukami, Hideo Ohno

    Applied Physics Letters 112 (19) 2018年5月7日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.5027855  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    Magnetic heterostructures consisting of high-resistivity (238 ± 5 μΩ cm)-W/CoFeB/MgO are prepared by sputtering and their spin-orbit torques are evaluated as a function of W thickness through an extended harmonic measurement. W thickness dependence of the spin-orbit torque with the Slonczewski-like symmetry is well described by the drift-diffusion model with an efficiency parameter, the so-called effective spin Hall angle, of -0.62 ± 0.03. In contrast, the field-like spin-orbit torque is one order of magnitude smaller than the Slonczewski-like torque and shows no appreciable dependence on the W thickness, suggesting a different origin from the Slonczewski-like torque. The results indicate that high-resistivity W is promising for low-current and reliable spin-orbit torque-controlled devices.

  76. Time and spatial evolution of spin-orbit torque-induced magnetization switching in W/CoFeB/MgO structures with various sizes 査読有り

    Chaoliang Zhang, Shunsuke Fukami, Samik Dutta Gupta, Hideo Sato, Hideo Ohno

    Japanese Journal of Applied Physics 57 (4) 2018年4月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/JJAP.57.04FN02  

    ISSN:0021-4922

    eISSN:1347-4065

    詳細を見る 詳細を閉じる

    We study spin-orbit torque (SOT) switching in W/CoFeB/MgO structures with various dot sizes (120-3500 nm) using pulsed current of various widths τ (800 ps-100 ms) to examine the time and spatial evolution of magnetization switching. We show that the switching behavior and the resultant threshold switching current density J strongly depend on device size and pulse width. The switching mode in a 3500nm dot device changes from probabilistic switching to reproducible partial switching as τ decreases. At τ = 800 ps, J becomes more than 3 times larger than that in the long-pulse regime. A decrease in dot size to 700nm does not significantly change the switching characteristics, suggesting that domain-wall propagation among the nucleated multiple domains governs switching. In contrast, devices with further reduced size (120 nm) show normal full switching with increasing probability with current and insignificant dependence of J on τ, indicating that nucleation governs switching. th th th

  77. Evaluation of energy barrier of CoFeB/MgO magnetic tunnel junctions with perpendicular easy axis using retention time measurement 査読有り

    Eli Christopher Inocencio Enobio, Mathias Bersweiler, Hideo Sato, Shunsuke Fukami, Hideo Ohno

    Japanese Journal of Applied Physics 57 (4) 2018年4月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/JJAP.57.04FN08  

    ISSN:0021-4922

    eISSN:1347-4065

    詳細を見る 詳細を閉じる

    We investigate the energy barrier E that determines the thermal stability factor Δ, of CoFeB/MgO magnetic tunnel junctions (MTJs) with a perpendicular easy axis by retention time measurement as a function of temperature Tand junction diameter D. E decreases with increasing T for all the studied MTJs. The temperature at which any particular value of E is obtained tends to decrease with decreasing D, indicating that the magnetization reversal in the MTJs is described by reversal models other than the nucleation model. We find that the temperature dependence of E correlates with that of spontaneous magnetization through the power law scaling relationship, which enables us to determine Δ at temperatures different from those used in the retention time measurement.

  78. Electric-field effect on the easy cone angle of the easy-cone state in CoFeB/MgO investigated by ferromagnetic resonance 査読有り

    Atsushi Okada, Shun Kanai, Shunsuke Fukami, Hideo Sato, Hideo Ohno

    Applied Physics Letters 112 (17) 2018年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.5026418  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    We investigate the effect of an electric field on the cone angle of the easy-cone state in a CoFeB/MgO stack by ferromagnetic resonance as a function of temperature. We find that the easy cone state appears in the CoFeB/MgO system below 200 K. The application of electric field E modulates the effective first-order magnetic anisotropy energy constant, whereas the second-order magnetic anisotropy energy constant is almost independent of E, resulting in the variation of the cone angle by E. The present observation reveals the importance of the modulation of the magnetic anisotropy by E in magnetic tunnel junctions exhibiting an easy-cone state under spin-transfer-torque-induced switching.

  79. Stack Structure Dependence of Magnetic Properties of PtMn/[Co/Ni] Films for Spin-Orbit Torque Switching Device 査読有り

    William A. Borders, Shunsuke Fukami, Hideo Ohno

    IEEE Transactions on Magnetics 53 (11) 2017年11月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2017.2703817  

    ISSN:0018-9464

    eISSN:1941-0069

    詳細を見る 詳細を閉じる

    We investigate the stack structure dependence of magnetic properties on thin films that consist of an antiferromagnetic PtMn and a ferromagnetic Co/Ni multilayer for field-free spin-orbit torque-induced magnetization switching devices. Magnetic parameters, such as the spontaneous magnetization, effective and interfacial magnetic anisotropies, and exchange bias field are quantified as a function of stack structure. Engineering of the stack allows the improvement of current-induced magnetization switching characteristics compared with a previous work, which is confirmed using patterned Hall cross devices.

  80. Spintronics based random access memory: a review 査読有り

    Sabpreet Bhatti, Rachid Sbiaa, Atsufumi Hirohata, Hideo Ohno, Shunsuke Fukami, S. N. Piramanayagam

    Materials Today 20 (9) 530-548 2017年11月

    出版者・発行元:ELSEVIER SCI LTD

    DOI: 10.1016/j.mattod.2017.07.007  

    ISSN:1369-7021

    eISSN:1873-4103

    詳細を見る 詳細を閉じる

    This article reviews spintronics based memories, in particular, magnetic random access memory (MRAM) in a systematic manner. Debuted as a humble 4 Mb product by FreeScale in 2006, the MRAM has grown to a 256 Mb product of Everspin in 2016. During this period, MRAM has overcome several hurdles and have reached a stage, where the potential for MRAM is very promising. One of the main hurdles that the MRAM overcome between 2006 and 2016 is the way the information is written. The 4 Mb MRAM used a magnetic field based switching technology that would be almost impossible to scale below 100 nm. The 256 Mb MRAM, on the other hand uses a different writing mechanism based on Spin Transfer Torque (STT), which is scalable to very low dimensions. In addition to the difference in the writing mechanism, there has also been a major shift in the storage material. Whereas the 4 Mb MRAM used materials with in-plane magnetic anisotropy, the 256 Mb MRAM uses materials with a perpendicular magnetic anisotropy (PMA). MRAM based on PMA is also scalable to much higher densities. The paper starts with a brief history of memory technologies, followed by a brief description of the working principles of MRAM for novice. Reading information from MRAM, the technologies, materials and the physics behind reading of bits in MRAM are described in detail. As a next step, the physics and technologies involved in writing information are described. The magnetic field based writing and its limitations are described first, followed by an explanation of STT mechanism. The materials and physics behind storage of information is described next. MRAMs with in-plane magnetization, their layered material structure and the disadvantages are described first, followed by the advantages of MRAMs with perpendicular magnetization, their advantages etc. The technologies to improve writability and potential challenges and reliability issues are discussed next. Some of the future technologies that might help the industry to move beyond the conventional MRAM technology are discussed at the end of the paper, followed by a summary and an outlook.

  81. Spin-orbit torques and Dzyaloshinskii-Moriya interaction in PtMn/[Co/Ni] heterostructures 査読有り

    S. DuttaGupta, T. Kanemura, C. Zhang, A. Kurenkov, S. Fukami, H. Ohno

    Applied Physics Letters 111 (18) 2017年10月30日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.5005593  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    Antiferromagnet (AFM)/ferromagnet (FM) heterostructures with broken inversion symmetry are perceived to open new opportunities for nonvolatile spintronic devices. Previous studies of such systems have demonstrated an emergence of spin-orbit torques (SOTs) in the heterostructures which are strong enough to bring about magnetization reversal. The impact of broken inversion symmetry and spin-orbit coupling also leads to an emergence of the Dzyaloshinskii-Moriya interaction (DMI) which governs the magnetic configuration and magnetization reversal. In this work, we study the SOT-induced effective fields and DMI in a heterostructure with an antiferromagnetic PtMn layer and a ferromagnetic [Co/Ni] multilayer and compare the results with a reference Pt/[Co/Ni] system. Magnetotransport measurements reveal the same sign and similar magnitude of SOT-induced effective fields for the two systems while current-induced domain wall motion measurements under in-plane fields reveal the opposite sign and smaller magnitude of DMI at the PtMn/[Co/Ni] interface compared to the Pt/[Co/Ni]. The obtained results offer in-depth information concerning the manifestations of spin-orbit interactions in AFM/FM systems, which is key to understanding of static magnetic configuration and magnetization reversal for their possible applications in antiferromagnetic spintronics.

  82. Spin-orbit torque induced magnetization switching in Co/Pt multilayers 査読有り

    Butsurin Jinnai, Chaoliang Zhang, Aleksandr Kurenkov, Mathias Bersweiler, Hideo Sato, Shunsuke Fukami, Hideo Ohno

    Applied Physics Letters 111 (10) 2017年9月4日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.5001171  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    Spin-orbit torque (SOT)-induced magnetization switching in Co/Pt multilayer structures with a Pt buffer layer is studied aiming to realize SOT-magnetic random access memory (MRAM) devices with high thermal stability. Current-induced magnetization switching and effective fields are measured using Hall-bar devices. The switching efficiency, defined as a ratio of the areal anisotropy energy density to switching current density, increases with increasing the number of Co/Pt stacks. This trend is in accordance with the stacking number dependence of effective fields per unit current density. The effective spin-Hall angle of the Pt buffer layer for the sample with multiple Co/Pt stacks is significantly larger than that of Pt previously reported, suggesting a generation of SOT in Co/Pt multilayers. These results indicate that Co/Pt multilayers are promising for SOT-MRAM devices possessing high thermal stability and small switching current.

  83. An artificial neural network with an analogue spin-orbit torque device 査読有り

    W. A. Borders, H. Akima, S. Fukami, S. Moriya, S. Kurihara, A. Kurenkov, Y. Horio, S. Sato, H. Ohno

    2017 IEEE International Magnetics Conference, INTERMAG 2017 2017年8月10日

    出版者・発行元:Institute of Electrical and Electronics Engineers Inc.

    DOI: 10.1109/INTMAG.2017.8007937  

    詳細を見る 詳細を閉じる

    Since collective spin systems store digital information as their magnetization direction, development of nonvolatile memories for computers with the von Neumann architecture is one of the mainstream outlets of spintronics research pursued in the last several decades.

  84. Magnetization switching schemes for nanoscale three-terminal spintronics devices 査読有り

    Shunsuke Fukami, Hideo Ohno

    Japanese Journal of Applied Physics 56 (8) 2017年8月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/JJAP.56.0802A1  

    ISSN:0021-4922

    eISSN:1347-4065

    詳細を見る 詳細を閉じる

    Utilizing spintronics-based nonvolatile memories in integrated circuits offers a promising approach to realize ultralow-power and high-performance electronics. While two-terminal devices with spin-transfer torque switching have been extensively developed nowadays, there has been a growing interest in devices with a three-terminal structure. Of primary importance for applications is the efficient manipulation of magnetization, corresponding to information writing, in nanoscale devices. Here we review the studies of current-induced domain wall motion and spin-orbit torque-induced switching, which can be applied to the write operation of nanoscale three-terminal spintronics devices. For domain wall motion, the size dependence of device properties down to less than 20nm will be shown and the underlying mechanism behind the results will be discussed. For spin-orbit torque-induced switching, factors governing the threshold current density and strategies to reduce it will be discussed. A proof-ofconcept demonstration of artificial intelligence using an analog spin-orbit torque device will also be reviewed.

  85. Annealing temperature dependence of magnetic properties of CoFeB/MgO stacks on different buffer layers 査読有り

    Kyota Watanabe, Shunsuke Fukami, Hideo Sato, Shoji Ikeda, Fumihiro Matsukura, Hideo Ohno

    Japanese Journal of Applied Physics 56 (8) 2017年8月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/JJAP.56.0802B2  

    ISSN:0021-4922

    eISSN:1347-4065

    詳細を見る 詳細を閉じる

    We investigate the annealing temperature dependence of the magnetic properties of CoFeB/MgO stacks with different buffer materials (Mo, Ta, and W). For Mo and W, bcc-crystalline and amorphous-like films are prepared by changing the deposition conditions. A relatively small saturation magnetization is maintained after annealing up to 400 °C for the samples with bcc-W, bcc-Mo, and amorphous-like Mo buffers. A small variation in magnetic dead layer thickness with annealing is observed for the samples with bcc-crystalline buffer layers. The interfacial anisotropy is found to mainly depend on the element of the buffer layer used regardless of its crystalline structure, and is larger for the samples with W and Mo buffers than those with Ta buffer. The sample with bcc-Mo buffer shows the highest robustness against annealing among the studied systems. We give a systematic picture based on the thermochemistry that can reasonably explain the observed buffer layer dependence of the variations in magnetic properties with annealing.

  86. Use of analog spintronics device in performing neuro-morphic computing functions 査読有り

    Shunsuke Fukami, William A. Borders, Aleksandr Kurenkov, Chaoliang Zhang, Samik DuttaGupta, Hideo Ohno

    2017 5th Berkeley Symposium on Energy Efficient Electronic Systems, E3S 2017 - Proceedings 2018-January 1-3 2017年6月28日

    出版者・発行元:IEEE

    DOI: 10.1109/E3S.2017.8246168  

    詳細を見る 詳細を閉じる

    Since spintronics devices are capable of retaining digital information as -Their magnetization direction, development of nonvolatile memories, so-called magnetoresistive random access memories (MRAMs), to realize low-power integrated circuits with -The von Neumann architecture has been one of -The mainstream outlets of spintronics research pursued in -The last several decades. Meanwhile, neuromorphic-computing hardware with non-von Neumann architecture has started to attract a great deal of attention in -The field of microelectronics. Neuromorphic computing allows for completion of complex tasks at high speeds and at low power consumption levels that conventional von Neumann computers struggle with [1,2]. Recent researches point out that -The spintronics devices also have -The capable characteristics to model -The human brain [3-5]. In this presentation, we describe a proof-of-concept demonstration of an associative memory operation like -The human brain using a spintronics device [6]. For this purpose, we employ a recently-found spin-orbit torque (SOT) induced switching [7-9] device consisting of an antiferromagnet (AFM)/ ferromagnet (FM) stack structure [10-12], which shows an analogue-like resistance switching and thus serves as an artificial synapse in artificial neural networks.

  87. Current-induced magnetization switching in a nano-scale CoFeB-MgO magnetic tunnel junction under in-plane magnetic field 査読有り

    N. Ohshima, H. Sato, S. Kanai, J. Llandro, S. Fukami, F. Matsukura, H. Ohno

    AIP Advances 7 (5) 055927 2017年5月1日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4977224  

    ISSN:2158-3226

    eISSN:2158-3226

    詳細を見る 詳細を閉じる

    We study current-induced magnetization switching properties of a magnetic tunnel junction with junction diameter of 19 nm and resistance-area product of 6 Ωμm2 in the nanosecond regime with and without in-plane magnetic field. At zero field, for both parallel (P)-to-anti-parallel (AP) and AP-to-P switchings, the probability of switching P approaches unity with the increase of pulse voltage duration τP. However, under in-plane magnetic field, P for P-to-AP switching starts to saturate at a value lower than unity with increasing τP, while AP-to-P switching remains the same as in the absence of in-plane magnetic field. This in-plane field dependence of P can be partially explained by the influence of electric-field modulation of magnetic anisotropy. SW SW SW

  88. Magnetic domain-wall creep driven by field and current in Ta/CoFeB/MgO 査読有り

    S. DuttaGupta, S. Fukami, B. Kuerbanjiang, H. Sato, F. Matsukura, V. K. Lazarov, H. Ohno

    AIP Advances 7 (5) 055918 2017年5月1日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4974889  

    ISSN:2158-3226

    eISSN:2158-3226

    詳細を見る 詳細を閉じる

    Creep motion of magnetic domain wall (DW), thermally activated DW dynamics under subthreshold driving forces, is a paradigm to understand the interaction between driven interfaces and applied external forces. Previous investigation has shown that DW in a metallic system interacts differently with current and magnetic field, manifesting itself as different universality classes for the creep motion. In this article, we first review the experimental determination of the universality classes for current- and field-driven DW creeps in a Ta/CoFeB/MgO wire, and then elucidate the underlying factors governing the obtained results. We show that the nature of torque arising from current in association with DW configuration determines universality class for the current-induced creep in this system. We also discuss the correlation between the field-induced DW creep characteristics and structure observed by a transmission electron microscope. The observed results are expected to provide a deeper understanding for physics of DW motion in various magnetic materials.

  89. Atomic structure and electronic properties of MgO grain boundaries in tunnelling magnetoresistive devices 国際誌 査読有り

    Jonathan J. Bean, Mitsuhiro Saito, Shunsuke Fukami, Hideo Sato, Shoji Ikeda, Hideo Ohno, Yuichi Ikuhara, Keith P. McKenna

    Scientific Reports 7 45594-45594 2017年4月

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/srep45594  

    ISSN:2045-2322

    eISSN:2045-2322

    詳細を見る 詳細を閉じる

    Polycrystalline metal oxides find diverse applications in areas such as nanoelectronics, photovoltaics and catalysis. Although grain boundary defects are ubiquitous their structure and electronic properties are very poorly understood since it is extremely challenging to probe the structure of buried interfaces directly. In this paper we combine novel plan-view high-resolution transmission electron microscopy and first principles calculations to provide atomic level understanding of the structure and properties of grain boundaries in the barrier layer of a magnetic tunnel junction. We show that the highly [001] textured MgO films contain numerous tilt grain boundaries. First principles calculations reveal how these grain boundaries are associated with locally reduced band gaps (by up to 3 eV). Using a simple model we show how shunting a proportion of the tunnelling current through grain boundaries imposes limits on the maximum magnetoresistance that can be achieved in devices.

  90. スピン軌道トルク磁気メモリデバイスを用いた自己連想記憶

    秋間学尚, Borders William, 深見俊輔, 守谷 哲, 栗原祥太, Kurenkov Alexander, 下橋亮太, 堀尾喜彦, 佐藤茂雄, 大野英男

    電子情報通信学会総合大会講演論文集 S-31-S-31 2017年3月22日

  91. アナログ磁気メモリデバイスを用いた自己連想記憶システムの構築

    栗原祥太, 秋間学尚, William A. Borders, 深見俊輔, 守谷 哲, Aleksandr Kurenkov, 下橋亮太, 堀尾喜彦, 佐藤茂雄, 大野英男

    電子情報通信学会技術報告 116 (521) 127-132 2017年3月13日

    出版者・発行元:電子情報通信学会

    ISSN:0913-5685

  92. Device-size dependence of field-free spin-orbit torque induced magnetization switching in antiferromagnet/ferromagnet structures 査読有り

    A. Kurenkov, C. Zhang, S. DuttaGupta, S. Fukami, H. Ohno

    Applied Physics Letters 110 (9) 092410 2017年2月27日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4977838  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    We study spin-orbit torque induced magnetization switching in devices consisting of an antiferromagnetic PtMn and ferromagnetic Co/Ni multilayer with sizes ranging from 5 μm to 50 nm. As the size decreases, switching behavior changes from analogue-like to stepwise with several intermediate levels. The number of intermediate levels decreases with the decreasing size and finally evolves into a binary mode below a certain threshold. The results are found to be explained by a unique reversal process of this system, where ferromagnetic domains comprising a number of polycrystalline grains reverse individually and among the domains both out-of-plane and in-plane components of exchange bias vary.

  93. Analogue spin-orbit torque device for artificial-neural-network-based associative memory operation 査読有り

    William A. Borders, Hisanao Akima, Shunsuke Fukami, Satoshi Moriya, Shouta Kurihara, Yoshihiko Horio, Shigeo Sato, Hideo Ohno

    BIOINSPIRATION & BIOMIMETICS 12 (1) 2017年2月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/APEX.10.013007  

    ISSN:1748-3182

    eISSN:1748-3190

    詳細を見る 詳細を閉じる

    We demonstrate associative memory operations reminiscent of the brain using nonvolatile spintronics devices. Antiferromagnet-ferromagnet bilayer-based Hall devices, which show analogue-like spin-orbit torque switching under zero magnetic fields and behave as artificial synapses, are used. An artificial neural network is used to associate memorized patterns from their noisy versions. We develop a network consisting of a field-programmable gate array and 36 spin-orbit torque devices. An effect of learning on associative memory operations is successfully confirmed for several 3 x 3-block patterns. A discussion on the present approach for realizing spintronics-based artificial intelligence is given. (C) 2017 The Japan Society of Applied Physics

  94. Analogue spin-orbit torque device for artificial-neural-network-based associative memory operation 査読有り

    William A. Borders, Hisanao Akima, Shunsuke Fukami, Satoshi Moriya, Shouta Kurihara, Yoshihiko Horio, Shigeo Sato, Hideo Ohno

    Applied Physics Express 10 (1) 013007 2017年1月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/APEX.10.013007  

    ISSN:1882-0778

    eISSN:1882-0786

    詳細を見る 詳細を閉じる

    We demonstrate associative memory operations reminiscent of the brain using nonvolatile spintronics devices. Antiferromagnet-ferromagnet bilayer-based Hall devices, which show analogue-like spin-orbit torque switching under zero magnetic fields and behave as artificial synapses, are used. An artificial neural network is used to associate memorized patterns from their noisy versions. We develop a network consisting of a fieldprogrammable gate array and 36 spin-orbit torque devices. An effect of learning on associative memory operations is successfully confirmed for several 3 ' 3-block patterns. A discussion on the present approach for realizing spintronics-based artificial intelligence is given.

  95. Critical role of W deposition condition on spin-orbit torque induced magnetization switching in nanoscale W/CoFeB/MgO 査読有り

    C. Zhang, S. Fukami, K. Watanabe, A. Ohkawara, S. DuttaGupta, H. Sato, F. Matsukura, H. Ohno

    Applied Physics Letters 109 (19) 192405 2016年11月7日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4967475  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    We study the spin-orbit torque induced magnetization switching in W/CoFeB/MgO heterostructures with W deposited under different sputtering conditions. We show that the crystal structure and resistivity of W depend on the employed sputtering conditions. Switching current of nanoscale devices is smaller while effective anisotropy field is larger for the devices with more resistive W channel deposited at lower sputtering power and higher Ar gas pressure. The effective spin Hall angle evaluated from the switching probability varies by a factor of 2-3 depending on the W resistivity controlled by the sputtering conditions.

  96. A sub-ns three-terminal spin-orbit torque induced switching device 査読有り

    Shunsuke Fukami, Tetsuro Anekawa, Ayato Ohkawara, Chaoliang Zhang, Hideo Ohno

    Digest of Technical Papers - Symposium on VLSI Technology 2016-September 7573379 2016年9月21日

    出版者・発行元:IEEE

    DOI: 10.1109/VLSIT.2016.7573379  

    ISSN:0743-1562

    詳細を見る 詳細を閉じる

    We show a three-terminal spintronics memory device, which can be reliably switched by 0.5-ns current pulses with small magnitude. A new device geometry is employed, where spin-orbit torque is used for the write operation. We also show that an improved structure realizes magnetic field-free switching and employing a material other than the standard Ta can lead to a reduction of the switching current by more than half.

  97. A spin-orbit torque switching scheme with collinear magnetic easy axis and current configuration 査読有り

    S. Fukami, T. Anekawa, C. Zhang, H. Ohno

    Nature Nanotechnology 11 (7) 621-625 2016年7月1日

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/nnano.2016.29  

    ISSN:1748-3387

    eISSN:1748-3395

    詳細を見る 詳細を閉じる

    Spin-orbit torque, a torque brought about by in-plane current via the spin-orbit interactions in heavy-metal/ferromagnet nanostructures, provides a new pathway to switch the magnetization direction. Although there are many recent studies, they all build on one of two structures that have the easy axis of a nanomagnet lying orthogonal to the current, that is, along the z or y axes. Here, we present a new structure with the third geometry, that is, with the easy axis collinear with the current (along the x axis). We fabricate a three-terminal device with a Ta/CoFeB/MgO-based stack and demonstrate the switching operation driven by the spin-orbit torque due to Ta with a negative spin Hall angle. Comparisons with different geometries highlight the previously unknown mechanisms of spin-orbit torque switching. Our work offers a new avenue for exploring the physics of spin-orbit torque switching and its application to spintronics devices.

  98. Magnetic Properties of CoFeB-MgO Stacks with Different Buffer-Layer Materials (Ta or Mo) 査読有り

    Kyota Watanabe, Shunsuke Fukami, Hideo Sato, Fumihiro Matsukura, Hideo Ohno

    IEEE Transactions on Magnetics 52 (7) 7378950 2016年7月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2016.2514525  

    ISSN:0018-9464

    eISSN:1941-0069

    詳細を見る 詳細を閉じる

    We investigate the effect of the buffer-layer materials and their crystallographic structures on the magnetic properties of the CoFeB-MgO stacks. Amorphous Ta, amorphous Mo, and crystalline Mo are used as the buffer layer of CoFeB-MgO. The CoFeB-MgO stacks on both the Mo buffer layers show higher perpendicular anisotropy than that on Ta after 400-°C annealing. Difference is also seen between the samples with amorphous and crystalline Mo in the intermixing property between Mo and CoFeB; intermixing is much more unlikely for the crystalline sample. Magnetic damping constant is also evaluated from ferromagnetic resonance measurements. Samples with crystalline Mo buffer layer show smaller damping constant than those with Ta buffer layer after 400-°C annealing. This paper clarifies that the magnetic properties of CoFeB-MgO depend on the buffer-layer materials and their crystallinities.

  99. Current-Induced Magnetization Switching of CoFeB/Ta/[Co/Pd (Pt)]-Multilayers in Magnetic Tunnel Junctions with Perpendicular Anisotropy 査読有り

    Shinya Ishikawa, Eli C.I. Enobio, Hideo Sato, Shunsuke Fukami, Fumihiro Matsukura, Hideo Ohno

    IEEE Transactions on Magnetics 52 (7) 7378992 2016年7月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2016.2517098  

    ISSN:0018-9464

    eISSN:1941-0069

    詳細を見る 詳細を閉じる

    We investigate magnetic properties of CoFeB/Ta/[Co/Pd (Pt)] multilayers and properties of magnetic tunnel junctions (MTJs) with the structures as a recording layer. CoFeB/Ta/[Co/Pd] multilayer shows a lower damping constant α than that of CoFeB/Ta/[Co/Pt] multilayer. We evaluate current-induced magnetization switching (CIMS) properties of the MTJs with CoFeB/Ta/[Co/Pd (Pt)] multilayers with the junction diameter of 15 (13) nm that show similar thermal stability factor. CIMS is observed for the MTJ with a CoFeB/Ta/[Co/Pd] multilayer at zero magnetic field, whereas it is observed for the MTJ with the CoFeB/Ta/[Co/Pt] multilayer only in the presence of an external field.

  100. A spin-orbit torque switching scheme with collinear magnetic easy axis and current configuration 査読有り

    S. Fukami, T. Anekawa, C. Zhang, H. Ohno

    Nature Nanotechnology 11 (7) 621-625 2016年7月1日

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/nnano.2016.29  

    ISSN:1748-3387

    eISSN:1748-3395

    詳細を見る 詳細を閉じる

    Spin-orbit torque, a torque brought about by in-plane current via the spin-orbit interactions in heavy-metal/ferromagnet nanostructures, provides a new pathway to switch the magnetization direction. Although there are many recent studies, they all build on one of two structures that have the easy axis of a nanomagnet lying orthogonal to the current, that is, along the z or y axes. Here, we present a new structure with the third geometry, that is, with the easy axis collinear with the current (along the x axis). We fabricate a three-terminal device with a Ta/CoFeB/MgO-based stack and demonstrate the switching operation driven by the spin-orbit torque due to Ta with a negative spin Hall angle. Comparisons with different geometries highlight the previously unknown mechanisms of spin-orbit torque switching. Our work offers a new avenue for exploring the physics of spin-orbit torque switching and its application to spintronics devices.

  101. Magnetization switching by spin-orbit torque in an antiferromagnet-ferromagnet bilayer system. 国際誌 査読有り

    Shunsuke Fukami, Chaoliang Zhang, Samik DuttaGupta, Aleksandr Kurenkov, Hideo Ohno

    Nature materials 15 (5) 535-41 2016年5月

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/nmat4566  

    ISSN:1476-1122

    eISSN:1476-4660

    詳細を見る 詳細を閉じる

    Spin-orbit torque (SOT)-induced magnetization switching shows promise for realizing ultrafast and reliable spintronics devices. Bipolar switching of the perpendicular magnetization by the SOT is achieved under an in-plane magnetic field collinear with an applied current. Typical structures studied so far comprise a nonmagnet/ferromagnet (NM/FM) bilayer, where the spin Hall effect in the NM is responsible for the switching. Here we show that an antiferromagnet/ferromagnet (AFM/FM) bilayer system also exhibits a SOT large enough to switch the magnetization of the FM. In this material system, thanks to the exchange bias of the AFM, we observe the switching in the absence of an applied field by using an antiferromagnetic PtMn and ferromagnetic Co/Ni multilayer with a perpendicular easy axis. Furthermore, tailoring the stack achieves a memristor-like behaviour where a portion of the reversed magnetization can be controlled in an analogue manner. The AFM/FM system is thus a promising building block for SOT devices as well as providing an attractive pathway towards neuromorphic computing.

  102. Magnetization switching by spin–orbit torque in an antiferromagnet–ferromagnet bilayer system 査読有り

    Fukami, S, Zhang, C, DuttaGupta, S, Kurenkov, A, Ohno, H

    Nat. Mater. 15 (5) 535-541 2016年5月1日

    出版者・発行元:None

    DOI: 10.1038/nmat4566  

    ISSN:1476-1122

    eISSN:1476-4660

  103. Magnetization switching by spin-orbit torque in an antiferromagnet-ferromagnet bilayer system 査読有り

    Shunsuke Fukami, Chaoliang Zhang, Samik Duttagupta, Aleksandr Kurenkov, Hideo Ohno

    Nature Materials 15 (5) 535-541 2016年5月1日

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/nmat4566  

    ISSN:1476-1122

    eISSN:1476-4660

    詳細を見る 詳細を閉じる

    Spin-orbit torque (SOT)-induced magnetization switching shows promise for realizing ultrafast and reliable spintronics devices. Bipolar switching of the perpendicular magnetization by the SOT is achieved under an in-plane magnetic field collinear with an applied current. Typical structures studied so far comprise a nonmagnet/ferromagnet (NM/FM) bilayer, where the spin Hall effect in the NM is responsible for the switching. Here we show that an antiferromagnet/ferromagnet (AFM/FM) bilayer system also exhibits a SOT large enough to switch the magnetization of the FM. In this material system, thanks to the exchange bias of the AFM, we observe the switching in the absence of an applied field by using an antiferromagnetic PtMn and ferromagnetic Co/Ni multilayer with a perpendicular easy axis. Furthermore, tailoring the stack achieves a memristor-like behaviour where a portion of the reversed magnetization can be controlled in an analogue manner. The AFM/FM system is thus a promising building block for SOT devices as well as providing an attractive pathway towards neuromorphic computing.

  104. Adiabatic spin-transfer-torque-induced domain wall creep in a magnetic metal 査読有り

    S. DuttaGupta, S. Fukami, C. Zhang, H. Sato, M. Yamanouchi, F. Matsukura, H. Ohno

    Nature Physics 12 (4) 333-336 2016年4月

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/nphys3593  

    ISSN:1745-2473

    eISSN:1745-2481

    詳細を見る 詳細を閉じる

    The dynamics of elastic interfaces is a general field of interest in statistical physics, where magnetic domain wall has served as a prototypical example. Domain wall 'creep' under the action of sub-threshold driving forces with thermal activation is known to be described by a scaling law with a certain universality class, which represents the mechanism of the interaction of domain walls with the applied forces over the disorder of the system. Here we show different universality classes depending on the driving forces, magnetic field or spin-polarized current, in a metallic system, which have hitherto been seen only in a magnetic semiconductor. We reveal that an adiabatic spin-transfer torque plays a major role in determining the universality class of current-induced creep, which does not depend on the intricacies of material disorder. Our results shed light on the physics of the creep motion of domain walls and other elastic systems.

  105. Electric field control of Skyrmions in magnetic nanodisks 査読有り

    Y. Nakatani, M. Hayashi, S. Kanai, S. Fukami, H. Ohno

    Applied Physics Letters 108 (15) 152403 2016年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4945738  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    The control of magnetic Skyrmions confined in a nanometer scale disk using electric field pulses is studied by micromagnetic simulation. A stable Skyrmion can be created and annihilated by an electric field pulse depending on the polarity of the electric field. Moreover, the core direction of the Skyrmion can be switched using the same electric field pulses. Such creation and annihilation of Skyrmions, and its core switching do not require any magnetic field and precise control of the pulse length. This unconventional manipulation of magnetic texture using electric field pulses allows a robust way of controlling magnetic Skyrmions in nanodiscs, a path toward building ultralow power memory devices.

  106. Current-induced domain wall motion in magnetic nanowires with various widths down to less than 20nm 査読有り

    Shunsuke Fukami, Toru Iwabuchi, Hideo Sato, Hideo Ohno

    Japanese Journal of Applied Physics 55 (4) 04EN01 2016年4月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/JJAP.55.04EN01  

    ISSN:0021-4922

    eISSN:1347-4065

    詳細を見る 詳細を閉じる

    We experimentally and theoretically study the current-induced domain wall motion in magnetic nanowires with various widths, and discuss the issues concerning the domain wall motion in wires with reduced widths down to less than 20 nm. For Co/Ni nanowires, the threshold current density significantly increases as the width decreases below 30nm and the domain wall motion is not observed within the studied current density range for a number of devices with the wire width of around 20 nm. The relationship between the threshold current density and wire width is reasonably reproduced by a theoretical calculation based on the adiabatic spin-transfer torque model. The micromagnetic simulation suggests that high-anisotropy materials are promising for domain-wall-motion devices with wire widths beyond 20 nm.

  107. Adiabatic spin-transfer-torque-induced domain wall creep in a magnetic metal 査読有り

    S. DuttaGupta, S. Fukami, C. Zhang, H. Sato, M. Yamanouchi, F. Matsukura, H. Ohno

    Nature Physics 12 (4) 333-336 2016年4月

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/nphys3593  

    ISSN:1745-2473

    eISSN:1745-2481

    詳細を見る 詳細を閉じる

    The dynamics of elastic interfaces is a general field of interest in statistical physics, where magnetic domain wall has served as a prototypical example. Domain wall 'creep' under the action of sub-threshold driving forces with thermal activation is known to be described by a scaling law with a certain universality class, which represents the mechanism of the interaction of domain walls with the applied forces over the disorder of the system. Here we show different universality classes depending on the driving forces, magnetic field or spin-polarized current, in a metallic system, which have hitherto been seen only in a magnetic semiconductor. We reveal that an adiabatic spin-transfer torque plays a major role in determining the universality class of current-induced creep, which does not depend on the intricacies of material disorder. Our results shed light on the physics of the creep motion of domain walls and other elastic systems.

  108. Atomic-Scale Structure and Local Chemistry of CoFeB-MgO Magnetic Tunnel Junctions 国際誌 査読有り

    Zhongchang Wang, Mitsuhiro Saito, Keith P. McKenna, Shunsuke Fukami, Hideo Sato, Shoji Ikeda, Hideo Ohno, Yuichi Ikuhara

    Nano Letters 16 (3) 1530-1536 2016年3月9日

    出版者・発行元:AMER CHEMICAL SOC

    DOI: 10.1021/acs.nanolett.5b03627  

    ISSN:1530-6984

    eISSN:1530-6992

    詳細を見る 詳細を閉じる

    Magnetic tunnel junctions (MTJs) constitute a promising building block for future nonvolatile memories and logic circuits. Despite their pivotal role, spatially resolving and chemically identifying each individual stacking layer remains challenging due to spatially localized features that complicate characterizations limiting understanding of the physics of MTJs. Here, we combine advanced electron microscopy, spectroscopy, and first-principles calculations to obtain a direct structural and chemical imaging of the atomically confined layers in a CoFeB-MgO MTJ, and clarify atom diffusion and interface structures in the MTJ following annealing. The combined techniques demonstrate that B diffuses out of CoFeB electrodes into Ta interstitial sites rather than MgO after annealing, and CoFe bonds atomically to MgO grains with an epitaxial orientation relationship by forming Fe(Co)-O bonds, yet without incorporation of CoFe in MgO. These findings afford a comprehensive perspective on structure and chemistry of MTJs, helping to develop high-performance spintronic devices by atomistic design.

  109. Three-Terminal Spintronics Devices for Integrated Circuits 招待有り 査読有り

    Shunsuke Fukami, Chaoliang Zhang, Samik DuttaGupta, Aleksandr Kurenkov, Tetsuro Anekawa, Hideo Ohno

    7TH IEEE INTERNATIONAL NANOELECTRONICS CONFERENCE (INEC) 2016 2016年

    出版者・発行元:IEEE

    DOI: 10.1109/INEC.2016.7589372  

    ISSN:2159-3523

    詳細を見る 詳細を閉じる

    Spintronics-based integrated circuits open up a new pathway toward ultralow-power and high-performance computing systems. Three-terminal spintronics devices, which achieves fast and reliable operation due to a relaxed control of parameters, have attracted increasing attention. We here review our recent studies on spin-orbit torque induced magnetization switching, which can be applied to the write operation of the three-terminal devices. We demonstrate the switching in a new device geometry and in a new material system.

  110. Temperature dependence of energy barrier in CoFeB-MgO magnetic tunnel junctions with perpendicular easy axis 査読有り

    Y. Takeuchi, H. Sato, S. Fukami, F. Matsukura, H. Ohno

    Applied Physics Letters 107 (15) 152405 2015年10月12日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4933256  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    We investigate an energy barrier E that determines the thermal stability factor of nanoscale CoFeB-MgO magnetic tunnel junctions (MTJs) with a perpendicular easy axis as a function of temperature between 298 and 393 K. For the MTJs with a junction diameter above 43 nm, Ε is much smaller and less sensitive to the temperature than the magnetic anisotropy energy of the total recording volume. For the MTJ with a diameter of 33 nm, E and the anisotropy energy take about the same value and show similar temperature dependence. The results can be explained by considering a crossover of magnetization reversal mode from nucleation type to single-domain like type, as the device dimensions reduce.

  111. Fabrication of a 3000-6-input-LUTs embedded and block-level power-gated nonvolatile FPGA chip using p-MTJ-based logic-in-memory structure 査読有り

    D. Suzuki, M. Natsui, A. Mochizuki, S. Miura, H. Honjo, H. Sato, S. Fukami, S. Ikeda, T. Endoh, H. Ohno, T. Hanyu

    Digest of Technical Papers - Symposium on VLSI Technology 2015-August C172-C173 2015年8月25日

    出版者・発行元:IEEE

    DOI: 10.1109/VLSIT.2015.7223644  

    ISSN:0743-1562

    詳細を見る 詳細を閉じる

    A nonvolatile FPGA (NVFPGA) test chip, where 3000 6-input lookup table (LUT) circuits are embedded, is fabricated under 90nm CMOS/75nm perpendicular magnetic tunnel junction (p-MTJ) technologies. The use of a p-MTJ device makes data-backup-limitation free, which essentially eliminates damage control to nonvolatile storage devices. The use of a p-MTJ device also enables the extension towards dynamically reconfigurable logic paradigm. Since hardware components are shared among all the p-MTJ devices by the use of logic-in-memory structure, the effective area of the 6-input LUT circuit is reduced by 56% compared to that of an SRAM-based one. Moreover, block-level power gating, in which all the idle function blocks are optimally turned off in accordance with the operation mode, can minimize static power consumption of each tile. As a result, the total average power of the proposed NVFPGA is reduced by 81% in comparison with that of an SRAM-based FPGA under typical benchmark-circuit realizations.

  112. Three-terminal spintronics memory devices with perpendicular anisotropy 査読有り

    H. Ohno, S. Fukami

    2015 IEEE International Magnetics Conference, INTERMAG 2015 7157427 2015年7月14日

    出版者・発行元:IEEE

    DOI: 10.1109/INTMAG.2015.7157427  

    詳細を見る 詳細を閉じる

    The focus of spintronics memory device that constitutes MRAM has so far been largely on two-terminal magnetic tunnel junction with spin-transfer torque magnetization switching, because of its superior area efficiency. In a number of cases, however, where switching speed and relaxed control of parameters are more preferred than the reduced area, three-terminal spintronics device is an equally, if not more, attractive alternative. Here 'three-terminal' refers to the number of terminals used for read and write operations. This configuration allows realizing high-speed and high-reliability device operation, suitable for replacement of semiconductor-based working memories such as SRAMs but with nonvolatility and reduced area to overcome issues of scaling limit and increasing power consumption [1]. Two types of three-terminal devices are currently under development; one utilizes a current-induced domain wall (DW) motion and the other a spin-orbit torque (SOT) induced magnetization switching for their write operation. Here we review and compare their basic operation principles and the technological prospects.

  113. Proposal and demonstration of a new spin-orbit torque induced switching device 査読有り

    S. Fukami, T. Anekawa, C. Zhang, H. Ohno

    2015 IEEE International Magnetics Conference, INTERMAG 2015 7156648 2015年7月14日

    出版者・発行元:IEEE

    DOI: 10.1109/INTMAG.2015.7156648  

    詳細を見る 詳細を閉じる

    Magnetic tunnel junction (MTJ) devices with three-terminal cell structure are promising building blocks for ultralow-power and high-performance memories and integrated circuits due to their high-speed and high-reliability features [1]. The three-terminal devices with spin-orbit torque (SOT) switching were recently proposed and have intensively investigated for a couple of years [2-7]. The SOT devices proposed so far are divided by their structure into two types. Here we propose a new structure of SOT device that combines the advantages of the existing two structures and demonstrate its basic operation.

  114. Spin-orbit torque induced magnetization switching in nano-scale Ta/CoFeB/MgO 査読有り

    C. Zhang, S. Fukami, H. Sato, F. Matsukura, H. Ohno

    Applied Physics Letters 107 (1) 012401 2015年7月6日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4926371  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    We study the device size dependence of spin-orbit torque induced magnetization switching in a Ta/CoFeB/MgO structure with perpendicular easy axis. The miniaturization of the device from micrometer-sized wire to 80-nm dot results in the increase of the threshold current density J by one order, whereas J increases only slightly with further reducing the device size down to 30nm. No significant increase in J is seen, as the current pulse width decreases from 100ms down to 3ns. We reveal that the switching in devices at reduced size is reasonably well explained by the macrospin model, in which the effects of both the Slonczewski-like torque and field-like torque are included. th th th

  115. Thermal stability of a magnetic domain wall in nanowires 査読有り

    S. Fukami, J. Ieda, H. Ohno

    Physical Review B - Condensed Matter and Materials Physics 91 (23) 235401 2015年6月4日

    出版者・発行元:AMER PHYSICAL SOC

    DOI: 10.1103/PhysRevB.91.235401  

    ISSN:1098-0121

    eISSN:1550-235X

    詳細を見る 詳細を閉じる

    We study the thermal stability of a magnetic domain wall pinned in nanowires with various widths and thicknesses made of Co/Ni multilayers and analyze the effective volume that governs the thermal stability. We find that, above a critical wire width, the domain wall depinning is initiated by a subvolume excitation and that the critical width is dependent on the wire thickness. The obtained findings are supported by the distribution of critical current density for domain wall depinning and are qualitatively described by an analytical model in which the balance between the Zeeman energy and domain wall elastic energy is considered. We also show a different behavior between the device size dependence of the thermal stability and that of critical current, leading to an enhancement of domain wall motion efficiency with decreasing the device size.

  116. Dependence of magnetic properties of MgO/CoFeB/Ta stacks on CoFeB and Ta thicknesses 査読有り

    Kyota Watanabe, Shinya Ishikawa, Hideo Sato, Shoji Ikeda, Michihiko Yamanouchi, Shunsuke Fukami, Fumihiro Matsukura, Hideo Ohno

    Japanese Journal of Applied Physics 54 (4) 04DM04 2015年4月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/JJAP.54.04DM04  

    ISSN:0021-4922

    eISSN:1347-4065

    詳細を見る 詳細を閉じる

    We investigate the dependence of magnetic properties of MgO/CoFeB/Ta stacks on thicknesses of CoFeB ranging from 2 to 30 nm and Ta from 1 to 10nm before and after annealing at 300-400 °C for 1-3 h. The annealing increases the saturation magnetic moment per unit area and reduces the magnitude of the damping constant in CoFeB. The annealing effect becomes smaller with increasing CoFeB thickness and with decreasing Ta thickness, indicating that the effect is related to B diffusion from CoFeB to Ta. We show that the amount of diffused B can be controlled by Ta layer thickness and annealing duration.

  117. Perpendicular-anisotropy CoFeB-MgO based magnetic tunnel junctions scaling down to 1X nm 査読有り

    S. Ikeda, H. Sato, H. Honjo, E. C.I. Enobio, S. Ishikawa, M. Yamanouchi, S. Fukami, S. Kanai, F. Matsukura, T. Endoh, H. Ohno

    Technical Digest - International Electron Devices Meeting, IEDM 2015-February (February) 33.2.1-33.2.4 2015年2月20日

    出版者・発行元:IEEE

    DOI: 10.1109/IEDM.2014.7047160  

    ISSN:0163-1918

    詳細を見る 詳細を閉じる

    CoFeB-MgO based magnetic tunnel junction with perpendicular easy axis (p-MTJ) shows a high potential to be used in spintronics based very large scale integrated circuits and spin-transfer-torque magnetorestive random access memories. In this paper, we review development of p-MTJ using single CoFeB-MgO and double CoFeB-MgO interface structures. The TMR ratio shows 164% after annealing at 400 °C, indicating the CoFeB-MgO p-MTJs have capability for back-end-of-line. Scaling properties of p-MTJs using double CoFeB-MgO interface structure are also reviewed.

  118. Spintronics: from basic research to VLSI application 査読有り

    S. Kanai, F. Matsukura, H. Sato, S. Fukami

    Association of Aisa Pacific Physical Societies, AAPPS 25 4-11 2015年2月

  119. Localized precessional mode of domain wall controlled by magnetic field and dc current 査読有り

    Ryo Hiramatsu, Kab Jin Kim, Takuya Taniguchi, Takayuki Tono, Takahiro Moriyama, Shunsuke Fukami, Michihiko Yamanouchi, Hideo Ohno, Yoshinobu Nakatani, Teruo Ono

    Applied Physics Express 8 (2) 023003-023003 2015年2月1日

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/APEX.8.023003  

    ISSN:1882-0778

    eISSN:1882-0786

    詳細を見る 詳細を閉じる

    We present evidence of a localized magnetic domain-wall (DW) oscillator in Co/Ni nanowires. It is found that a DW is localized by the simultaneous application of a high magnetic field larger than the depinning field and a dc current smaller than the threshold current. A one-dimensional model and micromagnetic simulation reveal that the localized DW is in a precessional mode. Our results suggest that a localized magnetic DW oscillator can be realized by appropriately adjusting the magnetic field and dc current.

  120. 23pAD-1 磁場および電流によって制御された磁壁発振器

    平松 亮, Kim Kab-Jin, 谷口 卓也, 東野 隆之, 森山 貴広, 深見 俊輔, 山ノ内 路彦, 大野 英男, 仲谷 栄伸, 小野 輝男

    日本物理学会講演概要集 70 1196-1196 2015年

    出版者・発行元:一般社団法人日本物理学会

    DOI: 10.11316/jpsgaiyo.70.1.0_1196  

    ISSN:2189-079X

  121. Fabrication of a 3000-6-Input-LUTs Embedded and Block-Level Power-Gated Nonvolatile FPGA Chip Using p-MTJ-Based Logic-in-Memory Structure 査読有り

    D. Suzuki, M. Natsui, A. Mochizuki, S. Miura, H. Honjo, H. Sato, S. Fukami, S. Ikeda, T. Endoh, H. Ohno, T. Hanyu

    2015 SYMPOSIUM ON VLSI TECHNOLOGY (VLSI TECHNOLOGY) 2015-August 7231371-C173 2015年

    出版者・発行元:IEEE

    DOI: 10.1109/VLSIC.2015.7231371  

    ISSN:0743-1562

    詳細を見る 詳細を閉じる

    A nonvolatile FPGA (NVFPGA) test chip, where 3000 6-input lookup table (LUT) circuits are embedded, is fabricated under 90nm CMOS/75nm perpendicular magnetic tunnel junction (p-MTJ) technologies. The use of a p-MTJ device makes data-backup-limitation free, which essentially eliminates damage control to nonvolatile storage devices. The use of a p-MTJ device also enables the extension towards dynamically reconfigurable logic paradigm. Since hardware components are shared among all the p-MTJ devices by the use of logic-in-memory structure, the effective area of the 6-input LUT circuit is reduced by 56% compared to that of an SRAM-based one. Moreover, block-level power gating, in which all the idle function blocks are optimally turned off in accordance with the operation mode, can minimize static power consumption of each tile. As a result, the total average power of the proposed NVFPGA is reduced by 81% in comparison with that of an SRAM-based FPGA under typical benchmark-circuit realizations.

  122. CoFeB Thickness Dependence of Damping Constants for Single and Double CoFeB-MgO Interface Structures 査読有り

    Eli Christopher I. Enobio, Hideo Sato, Shunsuke Fukami, Fumihiro Matsukura, Hideo Ohno

    IEEE Magnetics Letters 6 5700303 2015年

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/LMAG.2015.2475718  

    ISSN:1949-307X

    詳細を見る 詳細を閉じる

    We investigate the CoFeB thickness dependence of the damping constant α of single and double CoFeB-MgO interface structures by vector-network-analyzer ferromagnetic resonance (VNA-FMR). The damping constant increases with decreasing the CoFeB thickness for the single interface structure, and the damping constant for the double-interface structure takes a similar value to that for the single-interface structures with the same CoFeB thickness.

  123. Domain wall motion device for nonvolatile memory and logic - size dependence of device properties 査読有り

    Shunsuke Fukami, Michihiko Yamanouchi, Shoji Ikeda, Hideo Ohno

    IEEE Transactions on Magnetics 50 (11) 6971556 2014年11月1日

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2014.2321396  

    ISSN:0018-9464

    eISSN:1941-0069

    詳細を見る 詳細を閉じる

    Current-induced magnetic domain wall (DW)-motion device with a three- or four-terminal structure has considerable potential to trigger a profound transformation in memory and logic technologies. In this paper, we give an overview of DW-motion devices and describe their structure, operation method, and characteristics. Previous studies on the DW motion in nanowires with a Co/Ni multilayer are also reviewed. We also report on the experimental results regarding device properties, such as critical current, the time and energy required to displace the DW in the device, and retention properties with various device sizes down to 20 nm. The results reveal that writing properties are enhanced while sufficient retention properties are maintained as the device size is reduced, indicating that the DW-motion device has high scalability and compatibility with conventional semiconductor-based cells as well as ultralow power capability.

  124. Material stack design with high tolerance to process-induced damage in domain wall motion device 査読有り

    Hiroaki Honjo, Shunsuke Fukami, Kunihiko Ishihara, Keizo Kinoshita, Yukihide Tsuji, Ayuka Morioka, Ryusuke Nebashi, Keiichi Tokutome, Noboru Sakimura, Michio Murahata, Sadahiko Miura, Tadahiko Sugibayashi, Naoki Kasai, Hideo Ohno

    IEEE Transactions on Magnetics 50 (11) 6971768 2014年11月1日

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2014.2325019  

    ISSN:0018-9464

    eISSN:1941-0069

    詳細を見る 詳細を閉じる

    We have developed a three-terminal domain wall motion (DWM) device. We found that its performance was significantly degraded by ion irradiation to the DWM materials under conventional etching conditions with Ar/NH /CO gas mixture plasma for the device fabrication. To avoid this process-induced damage (PID), we fabricated and optimized a new material stack, in which a thin Ta layer is inserted on top of the capping layer of the DWM layer We found that the new stack effectively prevented a decrease in DWM layer coercivity, an increase in the critical current, and a decrease in the switching probability owing to the high-etch selectivity of Ta. As a result, the switching property of the DWM cell was greatly improved by the newly developed DWM stacks with high tolerance to PID. 3

  125. Process-induced damage and its recovery for a CoFeB–MgO magnetic tunnel junction with perpendicular magnetic easy axis 査読有り

    K. Kinoshita, H. Honjo, S. Fukami, H. Sato, K. Mizunuma, K. Tokutome, M. Murahata, S. Ikeda, S. Miura, N. Kasai, H. Ohno

    Jpn. J. Appl. Phys. 53 (10) 103001 2014年10月1日

    出版者・発行元:None

    DOI: 10.7567/JJAP.53.103001  

    ISSN:0021-4922

    eISSN:1347-4065

  126. Properties of magnetic tunnel junctions with a MgO/CoFeB/Ta/CoFeB/MgO recording structure down to junction diameter of 11nm 査読有り

    H. Sato, E. C.I. Enobio, M. Yamanouchi, S. Ikeda, S. Fukami, S. Kanai, F. Matsukura, H. Ohno

    Applied Physics Letters 105 (6) 062403 2014年8月11日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4892924  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    We investigate properties of perpendicular anisotropy magnetic tunnel junctions (MTJs) with a recording structure of MgO/CoFeB/Ta/CoFeB/MgO down to junction diameter (D) of 11nm from 56nm. Thermal stability factor (Δ) of MTJ with the structure starts to decrease at D=30nm. D dependence of Δ agrees well with that expected from magnetic properties of blanket film taking into account the change in demagnetizing factors of MTJs. Intrinsic critical current (I<inf>C0</inf>) reduces with decrease of D in the entire investigated D range. A ratio of Δ to I<inf>C0</inf> shows continuous increase with decrease of D down to 11nm. © 2014 AIP Publishing LLC.

  127. Distribution of critical current density for magnetic domain wall motion 査読有り

    S. Fukami, M. Yamanouchi, Y. Nakatani, K. J. Kim, T. Koyama, D. Chiba, S. Ikeda, N. Kasai, T. Ono, H. Ohno

    Journal of Applied Physics 115 (17) 17D508 2014年5月7日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4866394  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    The bit-to-bit distribution of a critical current density for magnetic domain wall (DW) motion is studied using Co/Ni wires with various wire widths (ws). The distribution inherently decreases with the w, and the ratio of standard deviation to average is 9.8% for wires with w = 40 nm. It is found that a self-distribution within one device, which is evaluated through repeated measurement, is a dominant factor in the bit-to-bit distribution. Micromagnetic simulation reveals that the distribution originates from DW configuration, which varies with device size. © 2014 AIP Publishing LLC.

  128. Co/Pt multilayer-based magnetic tunnel junctions with a CoFeB/Ta insertion layer 査読有り

    S. Ishikawa, H. Sato, M. Yamanouchi, S. Ikeda, S. Fukami, F. Matsukura, H. Ohno

    Journal of Applied Physics 115 (17) 17C719 2014年5月7日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4862724  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    We investigate properties of magnetic tunnel junctions (MTJs) having a Co/Pt multilayer as a recording layer. A CoFeB layer is inserted between MgO barrier and the recording layer in order to enhance the tunnel magnetoresistance ratio. We show that an additional layer of Ta inserted between CoFeB and Co/Pt multilayer is effective in improving the MTJ properties after annealing. A high effective magnetic anisotropy energy per unit area over 1.2mJ/m is obtained after annealing at 300°C. Using a 1.6 nm-thick CoFeB insertion layer, both high thermal stability factor of 92 and high tunnel magnetoresistance ratio of 91% are achieved in a MTJ with 17 nm in diameter. © 2014 AIP Publishing LLC. 2

  129. Design and fabrication of a perpendicular magnetic tunnel junction based nonvolatile programmable switch achieving 40% less area using shared-control transistor structure 査読有り

    D. Suzuki, M. Natsui, A. Mochizuki, S. Miura, H. Honjo, K. Kinoshita, S. Fukami, H. Sato, S. Ikeda, T. Endoh, H. Ohno, T. Hanyu

    Journal of Applied Physics 115 (17) 17B742 2014年5月7日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4868332  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    A compact nonvolatile programmable switch (NVPS) using 90nm CMOS technology together with perpendicular magnetic tunnel junction (p-MTJ) devices is fabricated for zero-standby-power field-programmable gate array. Because routing information does not change once it is programmed into an NVPS, high-speed read and write accesses are not required and a write-control transistor can be shared among all the NVPSs, which greatly simplifies structure of the NVPS. In fact, the effective area of the proposed NVPS is reduced by 40% compared to that of a conventional MTJ-based NVPS. The instant on/off behavior without external nonvolatile memory access is also demonstrated using the fabricated test chip. © 2014 AIP Publishing LLC.

  130. Three-terminal magnetic tunneling junction device with perpendicular anisotropy CoFeB sensing layer 査読有り

    H. Honjo, S. Fukami, K. Ishihara, R. Nebashi, K. Kinoshita, K. Tokutome, M. Murahata, S. Miura, N. Sakimura, T. Sugibayashi, N. Kasai, H. Ohno

    Journal of Applied Physics 115 (17) 17B750 2014年5月7日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4868623  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    We demonstrated read and write characteristics of a three terminal memory device with a perpendicular anisotropy-free layer of a strip of [Co/Ni] and a low-switching perpendicular-anisotropy CoFeB/MgO sensing layer. This new design of the cell results in a small cell area. The switching magnetic field of the sensing layer can be decreased by changing sputtering gas for the Ta-cap from Ar to Kr. An electron energy-loss spectroscopy analysis of the cross-section of the magnetic tunneling junction (MTJ) revealed that the boron content in CoFeB with a Kr-sputtered Ta-cap was smaller than that with an Ar-sputtered one. A change in resistance for the MTJ was observed that corresponded to the magnetic switching of the Co/Ni wire and its magnetoresistance ratio and critical current were 90% and 0.8mA, respectively. © 2014 AIP Publishing LLC.

  131. Magnetization reversal induced by in-plane current in Ta/CoFeB/MgO structures with perpendicular magnetic easy axis 査読有り

    C. Zhang, M. Yamanouchi, H. Sato, S. Fukami, S. Ikeda, F. Matsukura, H. Ohno

    Journal of Applied Physics 115 (17) 2014年5月7日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4863260  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    We investigate in-plane current-induced magnetization reversal under an in-plane magnetic field in Hall bar shaped devices composed of Ta/CoFeB/MgO structures with perpendicular magnetic easy axis. The observed relationship between the directions of current and magnetization switching and Ta thickness dependence of magnetization switching current are accordance with those for magnetization reversal by spin transfer torque originated from the spin Hall effect in the Ta layer.

  132. Co/Pt multilayer based reference layers in magnetic tunnel junctions for nonvolatile spintronics VLSIs 査読有り

    Hideo Sato, Shoji Ikeda, Shunsuke Fukami, Hiroaki Honjo, Shinya Ishikawa, Michihiko Yamanouchi, Kotaro Mizunuma, Fumihiro Matsukura, Hideo Ohno

    Japanese Journal of Applied Physics 53 (4 SPEC. ISSUE) 04EM02 2014年4月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/JJAP.53.04EM02  

    ISSN:0021-4922

    eISSN:1347-4065

    詳細を見る 詳細を閉じる

    We investigated properties of Co/Pt multilayer for reference layer in CoFeB-MgO magnetic tunnel junctions with perpendicular easy axis. The sufficient thermal stability factor of 284 was obtained under zero applied field in 40-nm-diameter Co/Pt multilayer based reference layer annealed at 350 °C. By applying a synthetic ferrimagnetic (SyF) structure to the Co/Pt multilayer based reference layer, the shift of the center of minor resistance-magnetic field curves was suppressed, leading to higher thermal stability of antiparallel magnetization configuration than that without a SyF structure. © 2014 The Japan Society of Applied Physics.

  133. Plasma process induced physical damages on multilayered magnetic films for magnetic domain wall motion 査読有り

    Keizo Kinoshita, Hiroaki Honjo, Shunsuke Fukami, Ryusuke Nebashi, Keiichi Tokutome, Michio Murahata, Sadahiko Miura, Naoki Kasai, Shoji Ikeda, Hideo Ohno

    Japanese Journal of Applied Physics 53 (3 SPEC. ISSUE 2) 03DF03 2014年3月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/JJAP.53.03DF03  

    ISSN:0021-4922

    eISSN:1347-4065

    詳細を見る 詳細を閉じる

    The effect of ion irradiation on magnetic domain wall motion (DWM) in a perpendicularly magnetized Co/Ni multilayered film was investigated. The DWM in the Co/Ni multilayered film was sometimes inhibited owing to damage in Co/Ni induced by ion irradiation from Ar/NH3/CO plasma during the etching of the upper layer of a Co/Pt multilayered film depending on the etched depth over Co/Ni. When the DWM was disturbed, modifications of crystallinity were observed by transmission electron microscopy (TEM) near the etched surface region of Co/Ni. Also, the segregation of Pt which was knocked on from the upper layer of Co/Pt, was observed by energy dispersive X-ray line-scan analysis by TEM (TEM-EDX). In contrast to that, the sample which had fine DWM property showed clear lattice image of Co/Ni. A Monte Carlo simulation of Ar+ ion irradiation predicted an atom-displacement range of about 3.5nm depth from the etching surface when the ion acceleration voltage was 900V. It was deep enough to degrade the area near the top region of the Co/Ni multilayered magnetic thin film. Eliminating these physical modifications during the etching process would be the key to the fabrication of reliable nonvolatile devices using domain wall motion. © 2014 The Japan Society of Applied Physics.

  134. Effect of spin Hall torque on current-induced precessional domain wall motion 査読有り

    Yoko Yoshimura, Tomohiro Koyama, Daichi Chiba, Yoshinobu Nakatani, Shunsuke Fukami, Michihiko Yamanouchi, Hideo Ohno, Kab Jin Kim, Takahiro Moriyama, Teruo Ono

    Applied Physics Express 7 (3) 033005 2014年3月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/APEX.7.033005  

    ISSN:1882-0778

    eISSN:1882-0786

    詳細を見る 詳細を閉じる

    Two important mechanisms for current-induced domain wall (DW) dynamics, namely, precessional DW motion driven by the adiabatic spin transfer torque and steady DW motion induced by the spin Hall torque, have been proposed and experimentally confirmed. However, the effect of the spin Hall torque on precessional DW motion has not been reported yet. Here, we show that the spin Hall torque affects the precessional DW motion when the in-plane field is applied. It is found that the in-plane field induces a half rotation time difference during DW precession, which gives rise to the nonvanishing spin Hall torque on the precessional DW motion. © 2014 The Japan Society of Applied Physics.

  135. Journal of Applied Physics 査読有り

    C. Zhang, M. Yamanouchi, H .Sato, S. Fukami, S. Ikeda, F. Matsukura, H. Ohno

    Magnetization reversal induced by in-plane current in Ta/CoFeB/MgO structures with perpendicular magnetic easy axis 115 17C714(1)-17C714(3) 2014年1月29日

  136. A delay circuit with 4-terminal magnetic-random-access-memory device for power-efficient time- domain signal processing 査読有り

    Ryusuke Nebashi, Noboru Sakimura, Hiroaki Honjo, Ayuka Morioka, Yukihide Tsuji, Kunihiko Ishihara, Keiichi Tokutome, Sadahiko Miura, Shunsuke Fukami, Keizo Kinoshita, Takahiro Hanyu, Tetsuo Endoh, Naoki Kasai, Hideo Ohno, Tadahiko Sugibayashi

    Proceedings - IEEE International Symposium on Circuits and Systems 1588-1591 2014年

    出版者・発行元:Institute of Electrical and Electronics Engineers Inc.

    DOI: 10.1109/ISCAS.2014.6865453  

    ISSN:0271-4310

    詳細を見る 詳細を閉じる

    A delay circuit using four-terminal magnetic-random-access-memory (MRAM) devices was designed for power-efficient time-domain signal processing. A cell area of 6.4 μm was obtained using 90-nm CMOS/MRAM technologies. The basic operations to both store the data and control the delay time were confirmed on the fabricated test chips. In addition, we proposed a power-efficient neuromorphic core using the delay circuit. © 2014 IEEE. 2

  137. 10.5 A 90nm 20MHz fully nonvolatile microcontroller for standby-power-critical applications 査読有り

    Noboru Sakimura, Yukihide Tsuji, Ryusuke Nebashi, Hiroaki Honjo, Ayuka Morioka, Kunihiko Ishihara, Keizo Kinoshita, Shunsuke Fukami, Sadahiko Miura, Naoki Kasai, Tetsuo Endoh, Hideo Ohno, Takahiro Hanyu, Tadahiko Sugibayashi

    Digest of Technical Papers - IEEE International Solid-State Circuits Conference 57 184-185 2014年

    出版者・発行元:IEEE

    DOI: 10.1109/ISSCC.2014.6757392  

    ISSN:0193-6530

    詳細を見る 詳細を閉じる

    Recently there has been increased demand for not only ultra-low power, but also high performance, even in standby-power-critical applications. Sensor nodes, for example, need a microcontroller unit (MCU) that has the ability to process signals and compress data immediately. A previously reported 130nm CMOS and FeRAM-based MCU features zero-standby power and fast wakeup operation by incorporating FeRAM devices into logic circuits [1]. The 8MHz speed, however, was not sufficiently high to meet application requirements, and the FeRAM process also has drawbacks: low compatibility with standard CMOS, and write endurance limitations. A spintronics-based nonvolatile integrated circuit is a promising option to achieve zero standby power and high-speed operation, along with compatibility with CMOS processes. In this work, we demonstrate a fully nonvolatile 16b MCU using 90nm standard CMOS and three-terminal SpinRAM technology. It achieves 20MHz, 145μW/MHz operation with a 1V supply in the active state, and 4.5μW intermittent operation with 120ns wakeup time and 0.1% active ratio, without forwarding of re-boot code from memory. The features provide sufficiently long battery life to achieve maintenance-free sensor nodes. © 2014 IEEE.

  138. Advances in spintronics devices for microelectronics - From spin-transfer torque to spin-orbit torque 査読有り

    S. Fukami, H. Sato, M. Yamanouchi, S. Ikeda, F. Matsukura, H. Ohno

    Proceedings of the Asia and South Pacific Design Automation Conference, ASP-DAC 684-691 2014年

    出版者・発行元:IEEE

    DOI: 10.1109/ASPDAC.2014.6742970  

    ISSN:2153-6961

    詳細を見る 詳細を閉じる

    Recent advances in spintronics devices make it possible to open a new era of microelectronics. In this paper, we review the spintronics devices utilizing spin-transfer torques (STTs) and spin-orbit torques (SOTs) developed in recent years. The progresses of two-terminal STT device with CoFeB-MgO based magnetic tunnel junction (MTJ), three-terminal magnetic domain wall (DW) motion device with Co/Ni multilayer, and three-terminal SOT device with Cu-based channel are described. Integrated circuits with the developed spintronics devices are also reviewed. © 2014 IEEE.

  139. MgO/CoFeB/Ta/CoFeB/MgO recording structure with low intrinsic critical current and high thermal stability 査読有り

    H. Sato, M. Yamanouchi, S. Ikeda, S. Fukami, F. Matsukura, H. Ohno

    J. Magn. Soc. Jpn. 38 (2-2) 56-60 2014年

    出版者・発行元:日本磁気学会

    DOI: 10.3379/msjmag.1403R002  

    ISSN:1882-2924

  140. A Delay Circuit with 4-Terminal Magnetic-Random-Access-Memory Device for Power-Efficient Time-Domain Signal Processing 査読有り

    Ryusuke Nebashi, Noboru Sakimura, Hiroaki Honjo, Ayuka Morioka, Yukihide Tsuji, Kunihiko Ishihara, Keiichi Tokutome, Sadahiko Miura, Shunsuke Fukami, Keizo Kinoshita, Takahiro Hanyu, Tetsuo Endoh, Naoki Kasai, Hideo Ohno, Tadahiko Sugibayashi

    2014 IEEE INTERNATIONAL SYMPOSIUM ON CIRCUITS AND SYSTEMS (ISCAS) 1588-1591 2014年

    出版者・発行元:IEEE

    DOI: 10.1109/ISCAS.2014.6865453  

    ISSN:0271-4302

    詳細を見る 詳細を閉じる

    A delay circuit using four-terminal magnetic-random-access-memory (MRAM) devices was designed for power-efficient time-domain signal processing. A cell area of 6.4 mu m(2) was obtained using 90-nm CMOS/MRAM technologies. The basic operations to both store the data and control the delay time were confirmed on the fabricated test chips. In addition, we proposed a power-efficient neuromorphic core using the delay circuit.

  141. Applied Physics Letters 査読有り

    C. Zhang, M. Yamanouchi, H. Sato, S. Fukami, S. Ikeda, F. Matsukura, H. Ohno

    Magnetotransport measurements of current induced effective fields in Ta/CoFeB/MgO 103 262407(1)-262407(3) 2013年12月31日

  142. Magnetotransport measurements of current induced effective fields in Ta/CoFeB/MgO 査読有り

    Chaoliang Zhang, Michihiko Yamanouchi, Hideo Sato, Shunsuke Fukami, Shoji Ikeda, Fumihiro Matsukura, Hideo Ohno

    Applied Physics Letters 103 (26) 262407 2013年12月23日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4859656  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    We evaluate current-induced effective magnetic fields in perpendicularly magnetized Ta/CoFeB/MgO structures from the external magnetic field angle dependence of the Hall resistance. We confirm the presence of two components of effective fields. The dependence of their magnitudes on Ta thickness implies that both components are related to the spin current in Ta layer generated by the spin Hall effect. © 2013 AIP Publishing LLC.

  143. Fabrication of a Perpendicular-MTJ-Based Compact Nonvolatile Programmable Switch Using Shared-Write-Control-Transistor Structure 査読有り

    D. Suzuki, M. Natsui, A. Mochizuki, S. Miura, H. Honjo, K. Kinoshita, H. Sato, S. Fukami, S. Ikeda, T. Endoh, H. Ohno, T. Hanyu

    Abst. 58th Annual Conference on Magnetism and Magnetic Materials 233 2013年11月

  144. Current-induced effective fields detected by magnetotrasport measurements 査読有り

    Masashi Kawaguchi, Kazutoshi Shimamura, Shunsuke Fukami, Fumihiro Matsukura, Hideo Ohno, Takahiro Moriyama, Daichi Chiba, Teruo Ono

    Applied Physics Express 6 (11) 113002 2013年11月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/APEX.6.113002  

    ISSN:1882-0778

    eISSN:1882-0786

    詳細を見る 詳細を閉じる

    We show that the angle-dependent Hall measurement is an effective method to determine the current-induced effective fields by investigating MgO/Fe/Ta and MgO/Fe/Pt/Ta multilayer structures. The experimentally obtained Hall resistance under a relatively large dc electrical current is well described by considering two components of current-induced effective fields, which may be related to the spin Hall effect and the Rashba effect. The directions of the effective fields are consistent with and their magnitudes are comparable to those reported previously for similar multilayer structures. © 2013 The Japan Society of Applied Physics.

  145. Applied Physics Express 査読有り

    M. Kawaguchi, K. Shimamura, S. Fukami, F. Matsukura, H. Ohno, T. Moriyama, D. Chiba, T. Ono

    Current-induced effectivve fields detected by magnetotransport measurements 6 113002(1)-113002(4) 2013年10月18日

  146. Demonstration of a Nonvolatile Processor Core Chip with Software-Controlled Three-Terminal MRAM Cells for Standby-Power Critical Applications 査読有り

    R. Nebashi, Y. Tsuji, H. Honjo, N. Sakimura, A. Morioka, K. Tokutome, S. Miura, S. Fukami, M. Yamanouchi, K. Kinoshita, T. Hanyu, T. Endoh, N. Kasai, H. Ohno, T. Sugibayashi

    2013 International Conference on Solid State Devices and Materials (SSDM) M-8-3 1102-1103 2013年9月24日

  147. Nature Communications 査読有り

    S. Fukami, M. Yamanouchi, S. Ikeda, H. Ohno

    Depinning probability of a magnetic domain wall in nanowires by spin-polarized currents 4 1-7 2013年8月15日

  148. Domain wall pinning by a stray field from NiFe on a Co/Ni nanowire 査読有り

    R. Hiramatsu, T. Koyama, H. Hata, T. Ono, D. Chiba, S. Fukami, N. Ishiwata

    Journal of the Korean Physical Society 63 (3) 608-611 2013年8月

    出版者・発行元:KOREAN PHYSICAL SOC

    DOI: 10.3938/jkps.63.608  

    ISSN:0374-4884

    eISSN:1976-8524

    詳細を見る 詳細を閉じる

    We have investigated the influence of a stray field on a magnetic domain wall (DW). The depinning fields of a DW in a perpendicularly magnetized Co/Ni nanowire with partly-stacked Ni Fe /SiO islands on it was measured. The depinning field for the wire with Ni Fe /SiO was found to be higher than that for the wire without the stack, indicating that the stray field from the Ni Fe /SiO stack clearly served as an artificial pinning site for the DW. The magnetic force microscopy observation evidenced that the DW was pinned near the Ni Fe stack. © 2013 The Korean Physical Society. 81 19 2 81 19 2 81 19 2 81 19

  149. IEEE Transactions on Magnetics 査読有り

    H. Sato, M. Yamanouchi, S. Ikeda, S. Fukami, F. Matsukura, H. Ohno

    MgO/CoFeB/Ta/CoFeB/MgO recording structure in magnetic tunnel junctions with perpendicular easy axis 49 (7) 4437-4440 2013年7月7日

  150. Electric field modulation of magnetic anisotropy in MgO/Co/Pt structure 査読有り

    Kihiro Yamada, Haruka Kakizakai, Kazutoshi Shimamura, Masashi Kawaguchi, Shunsuke Fukami, Nobuyuki Ishiwata, Daichi Chiba, Teruo Ono

    Applied Physics Express 6 (7) 073004 2013年7月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/APEX.6.073004  

    ISSN:1882-0778

    eISSN:1882-0786

    詳細を見る 詳細を閉じる

    In this study, we have investigated perpendicular magnetic anisotropy in a MgO/Co/Pt structure under an electric field. The change in the interface anisotropy energy in a MgO/Co stack upon the application of a gate voltage was determined by using a transport measurement technique. The result indicates that a decrease in the electron number at the surface of the Co layer leads to the enhancement of the perpendicular anisotropy energy at a temperature sufficiently lower than the Curie temperature. © 2013 The Japan Society of Applied Physics.

  151. CoNi Films with perpendicular magnetic anisotropy prepared by alternate monoatomic layer deposition 査読有り

    Shunsuke Fukami, Hideo Sato, Michihiko Yamanouchi, Shoji Ikeda, Hideo Ohno

    Applied Physics Express 6 (7) 073010 2013年7月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/APEX.6.073010  

    ISSN:1882-0778

    eISSN:1882-0786

    詳細を見る 詳細を閉じる

    We investigate the magnetic properties of CoNi and CoPt films prepared by an alternate monoatomic layer deposition and discuss the possible existence of a metastable superlattice structure. We find that, as has been reported for the CoPt and CoPd films, the CoNi film also exhibits a perpendicular magnetic anisotropy when the monoatomic Co and Ni layers are stacked alternately, suggesting the possible formation of superlattice structure. Since the CoNi film contains neither noble nor rare-earth metals, it should be an attractive material system for applications. © 2013 The Japan Society of Applied Physics.

  152. Enhanced interface perpendicular magnetic anisotropy in Ta|CoFeB|MgO using nitrogen doped Ta underlayers 査読有り

    Jaivardhan Sinha, Masamitsu Hayashi, Andrew J. Kellock, Shunsuke Fukami, Michihiko Yamanouchi, Hideo Sato, Shoji Ikeda, Seiji Mitani, See Hun Yang, Stuart S.P. Parkin, Hideo Ohno

    Applied Physics Letters 102 (24) 242405 2013年6月17日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4811269  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    We show that the magnetic characteristics of Ta|CoFeB|MgO magnetic heterostructures are strongly influenced by doping the Ta underlayer with nitrogen. In particular, the saturation magnetization drops upon doping the Ta underlayer, suggesting that the doped underlayer acts as a boron diffusion barrier. In addition, the thickness of the magnetic dead layer decreases with increasing nitrogen doping. Surprisingly, the interface magnetic anisotropy increases to ∼1.8 erg/cm when an optimum amount of nitrogen is introduced into the Ta underlayer. These results show that nitrogen doped Ta serves as a good underlayer for spintronic applications including magnetic tunnel junctions and domain wall devices. © 2013 AIP Publishing LLC. 2

  153. Electrical endurance of Co/Ni wire for magnetic domain wall motion device 査読有り

    S. Fukami, M. Yamanouchi, H. Honjo, K. Kinoshita, K. Tokutome, S. Miura, S. Ikeda, N. Kasai, H. Ohno

    Applied Physics Letters 102 (22) 222410 2013年6月3日

    DOI: 10.1063/1.4809734  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    We investigated electrical endurance of perpendicularly magnetized Co/Ni wires, which are a promising candidate material system for current-induced domain wall motion device. Monitoring the wire resistance while applying dc stress is shown to be a promising way to evaluate the electrical breakdown. An electromigration model describes well the observed time-to-failure as a function of temperature and current density. The dc stress current density which leads to 10-yr lifetime with 50% failure at 150 °C was twice as large as the threshold current density for domain wall motion, suggesting that the device with Co/Ni wire is highly durable against electrical stresses. © 2013 AIP Publishing LLC.

  154. Three terminal magnetic tunnel junction utilizing the spin Hall effect of iridium-doped copper 査読有り

    Michihiko Yamanouchi, Lin Chen, Junyeon Kim, Masamitsu Hayashi, Hideo Sato, Shunsuke Fukami, Shoji Ikeda, Fumihiro Matsukura, Hideo Ohno

    Applied Physics Letters 102 (21) 212408 2013年5月27日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4808033  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    We show a three terminal magnetic tunnel junction (MTJ) with a 10-nm thick channel based on an interconnection material Cu with 10% Ir doping. By applying a current density of less than 10 A m to the channel, depending on the current direction, switching of a MTJ defined on the channel takes place. We show that spin transfer torque (STT) plays a critical role in determining the threshold current. By assuming the spin Hall effect in the channel being the source of the STT, the lower bound of magnitude of the spin Hall angle is evaluated to be 0.03. © 2013 AIP Publishing LLC. 12 -2

  155. Magnetic properties of MgO-[Co/Pt] multilayers with a CoFeB insertion layer 査読有り

    S. Ishikawa, H. Sato, M. Yamanouchi, S. Ikeda, S. Fukami, F. Matsukura, H. Ohno

    Journal of Applied Physics 113 (17) 17C721 2013年5月7日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4798499  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    Magnetic properties of MgO-[Co/Pt] multilayers with a CoFeB insertion layer were investigated and the structure was adopted as a recording layer in magnetic tunnel junctions (MTJs) with perpendicular magnetic easy-axis to attain a high thermal stability. Perpendicular easy-axis was obtained with the Pt thickness range of 0.6-1.2 nm and the CoFeB thickness range of 0.6-1.5 nm. As-made MTJs employing the CoFeB-[Co/Pt] multilayer structure as a recording layer showed tunnel magnetoresistance of 40 on average. A high thermal stability factor over 200 was obtained in the MTJs with the size of 25 nm in diameter. © 2013 American Institute of Physics.

  156. スピン論理集積回路における基本ゲートの高信頼化技術 査読有り

    辻幸秀, 根橋竜介, 崎村昇, 森岡あゆ香, 本庄弘明, 徳留圭一, 三浦貞彦, 鈴木哲広, 深見俊輔, 木下啓藏, 羽生貴弘, 遠藤哲郎, 笠井直記, 大野英男, 杉林

    信学技報, 113 (1) 41-46 2013年4月1日

    出版者・発行元:一般社団法人電子情報通信学会

    ISSN:0913-5685

    詳細を見る 詳細を閉じる

    磁壁移動型スピン素子を用いた不揮発性論理ゲートにおいてゲート内でスピン素子を冗長化させることで、1スピン素子に起こるエラー率をP(<<1)とした場合の論理ゲートのエラー率を〜2・Pから〜6・P^2に低減した。また、冗長化による以下のオーバーヘッド、(1)面積の増加、(2)実効的な読み出し抵抗の低下、(3)素子数増加による書き込み時の消費電力の増大、に関して検討した。

  157. Thickness dependence of current-induced domain wall motion in a Co/Ni multi-layer with out-of-plane anisotropy 査読有り

    Hironobu Tanigawa, Tetsuhiro Suzuki, Shunsuke Fukami, Katsumi Suemitsu, Norikazu Ohshima, Eiji Kariyada

    Applied Physics Letters 102 (15) 152410 2013年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4802266  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    Thickness dependence of current-induced domain wall (DW) motion in a perpendicularly magnetized [Co/Ni] multilayered wire containing Ta/Pt capping and Pt/Ta seed layers has been studied. The thickness of the magnetic layer was controlled by the stacking number, N. The threshold current density for driving DW had a local minimum at N 3 and the velocity of DW motion decreased with N. Estimation of carrier spin polarization from measurements of DW velocity revealed that a thinner Co/Ni stack adjacent to the Pt layers reduced the carrier spin polarization and the strength of adiabatic spin transfer torque. © 2013 AIP Publishing LLC. N

  158. Nature Materials 査読有り

    J. Kim, J. Sinha, M. Hayashi, M. Yamanouchi, S. Fukami, T. Suzuki, S. Mitani, H. Ohno

    Layer thickness dependence of the current-induced effective field vector in Ta/CoFeB/MgO 12 240-245 2013年3月

  159. Layer thickness dependence of the current-induced effective field vector in Ta|CoFeB|MgO. 国際誌 査読有り

    Junyeon Kim, Jaivardhan Sinha, Masamitsu Hayashi, Michihiko Yamanouchi, Shunsuke Fukami, Tetsuhiro Suzuki, Seiji Mitani, Hideo Ohno

    Nature materials 12 (3) 240-5 2013年3月

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/nmat3522  

    ISSN:1476-1122

    詳細を見る 詳細を閉じる

    Current-induced effective magnetic fields can provide efficient ways of electrically manipulating the magnetization of ultrathin magnetic heterostructures. Two effects, known as the Rashba spin orbit field and the spin Hall spin torque, have been reported to be responsible for the generation of the effective field. However, a quantitative understanding of the effective field, including its direction with respect to the current flow, is lacking. Here we describe vector measurements of the current-induced effective field in Ta|CoFeB|MgO heterostructrures. The effective field exhibits a significant dependence on the Ta and CoFeB layer thicknesses. In particular, a 1 nm thickness variation of the Ta layer can change the magnitude of the effective field by nearly two orders of magnitude. Moreover, its sign changes when the Ta layer thickness is reduced, indicating that there are two competing effects contributing to it. Our results illustrate that the presence of atomically thin metals can profoundly change the landscape for controlling magnetic moments in magnetic heterostructures electrically.

  160. Layer thickness dependence of the current-induced effective field vector in Ta vertical bar CoFeB vertical bar MgO 査読有り

    Junyeon Kim, Jaivardhan Sinha, Masamitsu Hayashi, Michihiko Yamanouchi, Shunsuke Fukami, Tetsuhiro Suzuki, Seiji Mitani, Hideo Ohno

    NATURE MATERIALS 12 (3) 240-245 2013年3月

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/NMAT3522  

    ISSN:1476-1122

    eISSN:1476-4660

    詳細を見る 詳細を閉じる

    Current-induced effective magnetic fields can provide efficient ways of electrically manipulating the magnetization of ultrathin magnetic heterostructures. Two effects, known as the Rashba spin orbit field and the spin Hall spin torque, have been reported to be responsible for the generation of the effective field. However, a quantitative understanding of the effective field, including its direction with respect to the current flow, is lacking. Here we describe vector measurements of the current-induced effective field in Ta vertical bar CoFeB vertical bar MgO heterostructrures. The effective field exhibits a significant dependence on the Ta and CoFeB layer thicknesses. In particular, a 1 nm thickness variation of the Ta layer can change the magnitude of the effective field by nearly two orders of magnitude. Moreover, its sign changes when the Ta layer thickness is reduced, indicating that there are two competing effects contributing to it. Our results illustrate that the presence of atomically thin metals can profoundly change the landscape for controlling magnetic moments in magnetic heterostructures electrically.

  161. Layer thickness dependence of the current-induced effective field vector in Ta|CoFeB|MgO 査読有り

    Junyeon Kim, Jaivardhan Sinha, Masamitsu Hayashi, Michihiko Yamanouchi, Shunsuke Fukami, Tetsuhiro Suzuki, Seiji Mitani, Hideo Ohno

    Nature Materials 12 (3) 240-245 2013年3月

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/nmat3522  

    ISSN:1476-1122

    eISSN:1476-4660

    詳細を見る 詳細を閉じる

    Current-induced effective magnetic fields can provide efficient ways of electrically manipulating the magnetization of ultrathin magnetic heterostructures. Two effects, known as the Rashba spin orbit field and the spin Hall spin torque, have been reported to be responsible for the generation of the effective field. However, a quantitative understanding of the effective field, including its direction with respect to the current flow, is lacking. Here we describe vector measurements of the current-induced effective field in Ta|CoFeB|MgO heterostructrures. The effective field exhibits a significant dependence on the Ta and CoFeB layer thicknesses. In particular, a 1 nm thickness variation of the Ta layer can change the magnitude of the effective field by nearly two orders of magnitude. Moreover, its sign changes when the Ta layer thickness is reduced, indicating that there are two competing effects contributing to it. Our results illustrate that the presence of atomically thin metals can profoundly change the landscape for controlling magnetic moments in magnetic heterostructures electrically. © 2013 Macmillan Publishers Limited. All rights reserved.

  162. 600MHz Nonvolatile Latch Based on a New MTJ/CMOS Hybrid Circuit Concept 査読有り

    Tetsuo Endoh, Shuta Togashi, Fumitaka Iga, Yasuhiro Yoshida, Takashi Ohsawa, Hiroki Koike, Shunsuke Fukami, Shoji Ikeda, Naoki Kasai, Noboru Sakimura, Takahiro Hanyu, Hideo Ohno, Tetsuo Endoh

    The 3nd CSIS International Symposium on Spintronics-based VLSIs 2013年1月31日

  163. Comprehensive study of CoFeB-MgO magnetic tunnel junction characteristics with single- and double-interface scaling down to 1X nm 査読有り

    H. Sato, T. Yamamoto, M. Yamanouchi, S. Ikeda, S. Fukami, K. Kinoshita, F. Matsukura, N. Kasai, H. Ohno

    Technical Digest - International Electron Devices Meeting, IEDM 6724550 2013年

    出版者・発行元:IEEE

    DOI: 10.1109/IEDM.2013.6724550  

    ISSN:0163-1918

    詳細を見る 詳細を閉じる

    We study characteristics of CoFeB-MgO magnetic tunnel junction with perpendicular easy-axis (p-MTJ) at a reduced dimension down to 1X nm fabricated by hard-mask process. CoFeB-MgO p-MTJ with double-interface shows higher thermal stability down to 1X nm than that with single-interface. Thermal stability factor of 58 and intrinsic critical current of 24 μA are obtained in the CoFeB-MgO magnetic tunnel junction with perpendicular easy-axis using double-interface structure at a diameter of 20 nmφ. © 2013 IEEE.

  164. 20-nm magnetic domain wall motion memory with ultralow-power operation 査読有り

    S. Fukami, M. Yamanouchi, K. J. Kim, T. Suzuki, N. Sakimura, D. Chiba, S. Ikeda, T. Sugibayashi, N. Kasai, T. Ono, H. Ohno

    Technical Digest - International Electron Devices Meeting, IEDM 6724553 2013年

    出版者・発行元:IEEE

    DOI: 10.1109/IEDM.2013.6724553  

    ISSN:0163-1918

    詳細を見る 詳細を閉じる

    We study the write and retention properties of magnetic domain wall (DW)-motion memory devices with the dimensions down to 20 nm. We find that the write current and time are scaled along with device size while sufficient thermal stability and low error rate are maintained. As a result, ultralow-power (a few fJ) and reliable operation is possible even at reduced dimensions. © 2013 IEEE.

  165. Fabrication of a 99%-energy-less nonvolatile multi-functional CAM chip using hierarchical power gating for a massively-parallel full-text-search engine 査読有り

    S. Matsunaga, N. Sakimura, R. Nebashi, Y. Tsuji, A. Morioka, T. Sugibayashi, S. Miura, H. Honjo, K. Kinoshita, H. Sato, S. Fukami, M. Natsui, A. Mochizuki, S. Ikeda, T. Endoh, H. Ohno, T. Hanyu

    Digest of Technical Papers - Symposium on VLSI Technology 6576611 2013年

    ISSN:0743-1562

    詳細を見る 詳細を閉じる

    A ternary content-addressable memory (TCAM)-based hardware called nonvolatile 'multi-functional CAM (MF-CAM)' is proposed for an ultra-low-energy 'full-text search' system in recent data centers. The proposed nonvolatile MF-CAM-based full-text search engine can perform parallel comparison while eliminating leakage energy by hierarchical power gating. By the massively parallel comparison with the hierarchical power gating, energy consumption of the proposed search engine is reduced within 1% in comparison with the conventional CPU-based full-text search system, where repetitive comparisons between the CPU and a memory consume much energy. © 2013 JSAP.

  166. Low-current domain wall motion MRAM with perpendicularly magnetized CoFeB/MgO magnetic tunnel junction and underlying hard magnets 査読有り

    T. Suzuki, H. Tanigawa, Y. Kobayashi, K. Mori, Y. Ito, Y. Ozaki, K. Suemitsu, T. Kitamura, K. Nagahara, E. Kariyada, N. Ohshima, S. Fukami, M. Yamanouchi, S. Ikeda, M. Hayashi, M. Sakao, H. Ohno

    Digest of Technical Papers - Symposium on VLSI Technology 6576703 2013年

    ISSN:0743-1562

    詳細を見る 詳細を閉じる

    We have developed magnetic domain wall (DW) motion cells with a perpendicularly magnetized CoFeB free layer and underlying hard magnets. Low current writing operation of 0.16 mA and a high MR ratio of 80% were attained for the 130-nm-wide free layer. Write/read operation for a 16kb array and high endurance features were also confirmed. © 2013 JSAP.

  167. MgO/CoFeB/Ta/CoFeB/MgO recording structure in magnetic tunnel junctions with perpendicular easy axis 査読有り

    Hideo Sato, Michihiko Yamanouchi, Shoji Ikeda, Shunsuke Fukami, Fumihiro Matsukura, Hideo Ohno

    IEEE Transactions on Magnetics 49 (7) 4437-4440 2013年

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2013.2251326  

    ISSN:0018-9464

    eISSN:1941-0069

    詳細を見る 詳細を閉じる

    Junction size (D) dependence of thermal stability factor (Δ) and intrinsic critical current (I 0) were investigated for MgO/CoFeB/Ta/CoFeB/MgO recording structure in magnetic tunnel junctions (MTJs) having a CoFeB reference layer and a synthetic ferrimagnetic (SyF) reference layer. Δ of the recording structure shows almost constant value down to 40 nm, whereas I 0 shows a linear dependence on the recording layer area, as similarly observed in recording structure with single-interface. Average absolute intrinsic critical current density is 3.5 MA/cm , which is comparable to previously reported value for recording structure with single-interface. A MgO/CoFeB(1.4)/Ta(0.4)/CoFeB(1.0)/MgO double-interface recording structure in MTJ with SyF reference layer shows Δ of 59 at D=29 nm. © 2013 IEEE. C C 2

  168. Two-barrier stability that allows low-power operation in current-induced domain-wall motion 国際誌 査読有り

    Kab Jin Kim, Ryo Hiramatsu, Tomohiro Koyama, Kohei Ueda, Yoko Yoshimura, Daichi Chiba, Kensuke Kobayashi, Yoshinobu Nakatani, Shunsuke Fukami, Michihiko Yamanouchi, Hideo Ohno, Hiroshi Kohno, Gen Tatara, Teruo Ono

    Nature Communications 4 2011-2011 2013年

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/ncomms3011  

    ISSN:2041-1723

    eISSN:2041-1723

    詳細を見る 詳細を閉じる

    Energy barriers in magnetization reversal dynamics have long been of interest because the barrier height determines the thermal stability of devices as well as the threshold force triggering their dynamics. Especially in memory and logic applications, there is a dilemma between the thermal stability of bit data and the operation power of devices, because larger energy barriers for higher thermal stability inevitably lead to larger magnetic fields (or currents) for operation. Here we show that this is not the case for current-induced magnetic domain-wall motion induced by adiabatic spin-transfer torque. By quantifying domain-wall depinning energy barriers by magnetic field and current, we find that there exist two different pinning barriers, extrinsic and intrinsic energy barriers, which govern the thermal stability and threshold current, respectively. This unique two-barrier system allows low-power operation with high thermal stability, which is impossible in conventional single-barrier systems. © 2013 Macmillan Publishers Limited. All rights reserved.

  169. Direct observation of domain wall motion in Co/Pt wire under gate electric field 査読有り

    Haruka Kakizakai, Kihiro Yamada, Masashi Kawaguchi, Kazutoshi Shimamura, Shunsuke Fukami, Nobuyuki Ishiwata, Daichi Chiba, Teruo Ono

    Japanese Journal of Applied Physics 52 (7 PART 1) 070206 2013年1月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.7567/JJAP.52.070206  

    ISSN:0021-4922

    eISSN:1347-4065

    詳細を見る 詳細を閉じる

    In this study, we have investigated magnetic domain wall motion under gate electric fields in a perpendicularly magnetized Co/Pt wire. The motion under a transparent gate electrode was directly monitored using a magneto-optical Kerr effect microscope. The domain wall velocity was determined as a function of temperature and gate voltage. It was found that this velocity could be modulated by up to two orders of magnitude by changing the gate voltage. © 2013 The Japan Society of Applied Physics.

  170. Depinning probability of a magnetic domain wall in nanowires by spin-polarized currents 査読有り

    S. Fukami, M. Yamanouchi, S. Ikeda, H. Ohno

    Nature Communications 4 2293 2013年

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/ncomms3293  

    ISSN:2041-1723

    eISSN:2041-1723

    詳細を見る 詳細を閉じる

    Current-induced magnetic domain wall motion is attractive for manipulating magnetization direction in spintronics devices, which open a new era of electronics. Up to now, in spite of a crucial significance to applications, investigation on a current-induced domain wall depinning probability, especially in sub-nano to a-few-nanosecond range has been lacking. Here we report on the probability of the depinning in perpendicularly magnetized Co/Ni nanowires in this timescale. A high depinning probability was obtained even for 2-ns pulses with a current density of less than 10 A m . A one-dimensional Landau-Lifshitz-Gilbert calculation taking into account thermal fluctuations reproduces well the experimental results. We also calculate the depinning probability as functions of various parameters and found that parameters other than the coercive field do not affect the transition width of the probability. These findings will allow one to design high-speed and reliable magnetic devices based on the domain wall motion. © 2013 Macmillan Publishers Limited. All rights reserved. 12 -2

  171. Spin 査読有り

    S. Ikeda, H. Sato, M. Yamanouchi, H. Gan, K. Miura, K. Mizunuma, S. Kanai, S. Fukami, F. Matsukura, N. Kasai, H. Ohno

    Recent progress of perpendicular anisotropy magnetic tunnel junctions for nonvolatile VLSI 2 (3) 1240003(1)-1240003(12) 2012年12月4日

    DOI: 10.4018/ijfsa.2012070101  

  172. Recent progress of perpendicular anisotropy magnetic tunnel junctions for nonvolatile vlsi 査読有り

    Shoji Ikeda, Hideo Sato, Michihiko Yamanouchi, Huadong Gan, Katsuya Miura, Kotaro Mizunuma, Shun Kanai, Shunsuke Fukami, Fumihiro Matsukura, Naoki Kasai, Hideo Ohno

    SPIN 2 (3) 1240003 2012年9月1日

    DOI: 10.1142/S2010324712400036  

    ISSN:2010-3247

    eISSN:2010-3255

    詳細を見る 詳細を閉じる

    We review recent developments in magnetic tunnel junctions with perpendicular easy axis (p-MTJs) for nonvolatile very large scale integrated circuits (VLSIs). So far, a number of material systems such as rare-earth/transition metal alloys, L1 -ordered (Co, Fe)-Pt alloys, Co/(Pd, Pt) multilayers, and ferromagnetic-alloy/oxide stacks have been proposed as electrodes in p-MTJs. Among them, p-MTJs with single or double ferromagnetic-alloy/oxide stacks, particularly CoFeB-MgO, were shown to have high potential to satisfy major requirements for integration. 0

  173. Current-induced magnetic domain wall motion below intrinsic threshold triggered by Walker breakdown 査読有り

    T. Koyama, K. Ueda, K. J. Kim, Y. Yoshimura, D. Chiba, K. Yamada, J. P. Jamet, A. Mougin, A. Thiaville, S. Mizukami, S. Fukami, N. Ishiwata, Y. Nakatani, H. Kohno, K. Kobayashi, T. Ono

    Nature Nanotechnology 7 (10) 635-639 2012年8月26日

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/nnano.2012.151  

    ISSN:1748-3387

    eISSN:1748-3395

    詳細を見る 詳細を閉じる

    Controlling the position of a magnetic domain wall with electric current may allow for new types of non-volatile memory and logic devices. To be practical, however, the threshold current density necessary for domain wall motion must be reduced below present values. Intrinsic pinning due to magnetic anisotropy, as recently observed in perpendicularly magnetized Co/Ni nanowires, has been shown to give rise to an intrinsic current threshold J th 0. Here, we show that domain wall motion can be induced at current densities 40% below J th 0 when an external magnetic field of the order of the domain wall pinning field is applied. We observe that the velocity of the domain wall motion is the vector sum of current- and field-induced velocities, and that the domain wall can be driven against the direction of a magnetic field as large as 2,000Â Oe, even at currents below J th 0. We show that this counterintuitive phenomenon is triggered by Walker breakdown, and that the additive velocities provide a unique way of simultaneously determining the spin polarization of current and the Gilbert damping constant.

  174. Observation of magnetic domain-wall dynamics transition in Co/Ni multilayered nanowires 査読有り

    Kab Jin Kim, D. Chiba, K. Kobayashi, S. Fukami, M. Yamanouchi, H. Ohno, Soong Geun Je, Sug Bong Choe, T. Ono

    Applied Physics Letters 101 (2) 022407 2012年7月9日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4733667  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    We observe a transition of domain-wall (DW) dynamics in ferromagnetic wires made of Co/Ni multilayers by use of transport measurement. As the wire width reduces, DW dynamics exhibits a transition from dendrite growth to pure DW motion. The threshold width is found to be about 300 nm and strongly depends on the relative dragging direction of the magnetic field and the current on DW: parallel (antiparallel) direction results in much smaller (larger) threshold width. It should be considered as a building block for DW-motion-based device applications. © 2012 American Institute of Physics.

  175. Perpendicular-anisotropy CoFeB-MgO magnetic tunnel junctions with a MgO/CoFeB/Ta/CoFeB/MgO recording structure 査読有り

    H. Sato, M. Yamanouchi, S. Ikeda, S. Fukami, F. Matsukura, H. Ohno

    Applied Physics Letters 101 (2) 022414 2012年7月9日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4736727  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    We investigated perpendicular CoFeB-MgO magnetic tunnel junctions (MTJs) with a recording structure consisting of two CoFeB-MgO interfaces, MgO/CoFeB (1.6 nm)/Ta (0.4 nm)/CoFeB (1.0 nm)/MgO. Thermal stability factor of MTJ with the structure having junction size of 70 nm was increased by a factor of 1.9 from the highest value of perpendicular MTJs with single CoFeB-MgO interface having the same device structure. On the other hand, intrinsic critical current for spin transfer torque switching of the double- and single-interface MTJs was comparable. © 2012 American Institute of Physics.

  176. Electric field-induced magnetization reversal in a perpendicular-anisotropy CoFeB-MgO magnetic tunnel junction 査読有り

    H. Sato, M. Yamanouchi, S. Ikeda, S. Fukami, F. Matsukura, H. Ohno

    Applied Physics Letters 101 022414 2012年7月

    DOI: 10.1063/1.4753816  

  177. Current-induced domain wall motion in perpendicularly magnetized Co/Ni nanowire under in-plane magnetic fields 査読有り

    Yoko Yoshimura, Tomohiro Koyama, Daichi Chiba, Yoshinobu Nakatani, Shunsuke Fukami, Michihiko Yamanouchi, Hideo Ohno, Teruo Ono

    Applied Physics Express 5 (6) 063001 2012年6月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/APEX.5.063001  

    ISSN:1882-0778

    eISSN:1882-0786

    詳細を見る 詳細を閉じる

    We have investigated current-induced domain wall (DW) motion in a perpendicularly magnetized Co/Ni nanowire under in-plane (hard-axis) and perpendicular (easy-axis) external magnetic fields. The DW velocity was found to be almost independent of them in the range of ±50 Oe. The result shows that reliable device operation against an external magnetic field disturbance can be achieved using the present system. © 2012 The Japan Society of Applied Physics.

  178. Electric field effect on magnetization of an Fe ultrathin film 査読有り

    Masashi Kawaguchi, Kazutoshi Shimamura, Shimpei Ono, Shunsuke Fukami, Fumihiro Matsukura, Hideo Ohno, Daichi Chiba, Teruo Ono

    Applied Physics Express 5 (6) 063307 2012年6月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/APEX.5.063007  

    ISSN:1882-0778

    eISSN:1882-0786

    詳細を見る 詳細を閉じる

    We show the effect of an applied electric field on the magnetization of an Fe ultrathin film. An electric double layer was formed at the interface between an ionic liquid and the Fe layer by the accumulation of ions caused by applying a gate voltage, and a large electric field was exerted on the Fe film surface. The saturation magnetization increased when the electron density at the Fe surface increased. A change in the saturation magnetization of ∼50% was observed by applying a gate voltage of ±2 V. © 2012 The Japan Society of Applied Physics.

  179. Temperature dependence of carrier spin polarization determined from current-induced domain wall motion in a Co/Ni nanowire 査読有り

    K. Ueda, T. Koyama, R. Hiramatsu, D. Chiba, S. Fukami, H. Tanigawa, T. Suzuki, N. Ohshima, N. Ishiwata, Y. Nakatani, K. Kobayashi, T. Ono

    Applied Physics Letters 100 (20) 202407 2012年5月14日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4718599  

    ISSN:0003-6951

    eISSN:1077-3118

    詳細を見る 詳細を閉じる

    We have investigated the temperature dependence of the current-induced magnetic domain wall (DW) motion in a perpendicularly magnetized Co/Ni nanowire at various temperatures and with various applied currents. The carrier spin polarization was estimated from the measured domain wall velocity. We found that it decreased more with increasing temperature from 100 K to 530 K than the saturation magnetization did. © 2012 American Institute of Physics.

  180. Spatial control of magnetic anisotropy for current induced domain wall injection in perpendicularly magnetized CoFeBMgO nanostructures 査読有り

    Masamitsu Hayashi, Michihiko Yamanouchi, Shunsuke Fukami, Jaivardhan Sinha, Seiji Mitani, Hideo Ohno

    Applied Physics Letters 100 (19) 192411 2012年5月7日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.4711016  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    Magnetic anisotropy of perpendicularly magnetized CoFeBMgO films is spatially tailored using depth controlled Ar ion etching with patterned etching masks. Nanowires with patterned etching have significantly reduced coercivity compared to those without the etching. We show that the sign of the anisotropy can be locally changed by partially etching the MgO layer, and as a consequence, 90° domain walls can be created at the boundary of etched/non-etched region. Direct current application to the nanowire can result in moving such 90° domain walls, which can prove as an efficient mean to inject domain walls into perpendicularly magnetized nanowires. © 2012 American Institute of Physics.

  181. 3端子磁壁移動型セルを用いた不揮発性コンテントアドレッサブルメモリ 査読有り

    根橋竜介, 崎村昇, 辻幸秀, 深見俊輔, 本庄弘明, 齊藤信作, 三浦貞彦, 石綿延行, 木下啓蔵, 羽生貴弘, 遠藤哲郎, 笠井直記, 大野英男, 杉林直彦

    信学技報 112 (15) 49-54 2012年4月1日

    出版者・発行元:一般社団法人電子情報通信学会

    ISSN:0913-5685

    詳細を見る 詳細を閉じる

    3端子磁壁移動型セルを用いた不揮発性コンテントアドレッサブルメモリを開発した。90nmのCMOSプロセスを用いて作製した、16KbのCAMマクロは5nsでサーチ動作できることを実証した。このスピードは、既存のSRAMベースのCAMとほぼ同等である。

  182. Magnetic tunneling junction with Fe/NiFeB free layer for magnetic logic circuits 査読有り

    H. Honjo, S. Fukami, R. Nebashi, N. Ishiwata, S. Miura, N. Sakimura, T. Sugibayashi, N. Kasai, H. Ohno

    Journal of Applied Physics 111 (7) 07C709 2012年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3675268  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    We have developed a shape varying magnetic tunneling junction (SVM) with a Fe/NiFeB free layer for use in magnetic logic circuits. Inserting the thin Fe film between an NiFeB free layer and MgO tunneling barrier improved the magnetoresistance (MR) ratio: it increased up to 130, as the thickness of the Fe film increased. In addition, the switching current distribution of the SVM was reduced to 8. By using NiFeB as a free layer, the roughness under the MgO was reduced and the crystallization of the MgO was enhanced. This led to both the high MR ratio and the low switching current distribution. Our developed Fe (0.4 nm)/NiFeB free layer satisfies the requirement of the MTJ's characteristics that the magnetic logic circuits operate with a high bit yield. © 2012 American Institute of Physics.

  183. Domain-wall-motion cell with perpendicular anisotropy wire and in-plane magnetic tunneling junctions 査読有り

    H. Honjo, S. Fukami, T. Suzuki, R. Nebashi, N. Ishiwata, S. Miura, N. Sakimura, T. Sugibayashi, N. Kasai, H. Ohno

    Journal of Applied Physics 111 (7) 07C903 2012年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3671437  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    A wire with perpendicular magnetic anisotropy (PA) is suitable for domain-wall-motion (DWM) cells because its critical current is small. However, it is not easy to design a cell consisting of a high magnetoresistance (MR) ratio magnetic tunneling junction (MTJ) and a DWM using PA material alone. We propose a combination of a PA-DWM element and in-plane (IP) MTJ for detection. The structure can be designed in a way that reduces the write current by the use of a perpendicular layer, yet maintains a high MR ratio by the independent use of in-plane material stacks. We fabricated a cell and ran tests to determine its read and write properties. A critical write current of 700 μA and a MR ratio of 50 were achieved. These properties are almost the same as when a DWM wire and in-plane MTJ are fabricated separately, which means it is possible to design the two elements independently. © 2012 American Institute of Physics.

  184. Attenuation of propagating spin wave induced by layered nanostructures 査読有り

    K. Sekiguchi, T. N. Vader, K. Yamada, S. Fukami, N. Ishiwata, S. M. Seo, S. W. Lee, K. J. Lee, T. Ono

    Applied Physics Letters 100 (13) 132411 2012年3月26日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3699020  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    Spin wave attenuation in the layered [FeNi / Pt] 6 / FeNi thin films was investigated by the time-domain electrical measurement. The spin-wave waveform was detected with an asymmetric coplanar strip transmission line, as an induced voltage flowing into a fast oscilloscope. We report that the amplitude of a spin-wave packet was systematically changed by controlling the thickness of a platinum layer, up to a maximum change of 50. The virtues of spin wave, ultrafast propagation velocity and non-reciprocal emission, are preserved in this manner. This means that the Pt layer can manipulate an arbitral power-level of spin-wave input signal (reliable attenuator). © 2012 American Institute of Physics.

  185. Electrical control of Curie temperature in cobalt using an ionic liquid film 査読有り

    K. Shimamura, D. Chiba, S. Ono, S. Fukami, N. Ishiwata, M. Kawaguchi, K. Kobayashi, T. Ono

    Applied Physics Letters 100 (12) 122402 2012年3月19日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3695160  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    The electric field effect on magnetization properties and Curie temperature of Co ultra-thin films has been investigated. An electric field is applied to a Co film by using an electric double layer (EDL) formed in a polymer film containing an ionic liquid. The change in the Curie temperature is ∼100 K by applying the gate voltage of ±2 V, suggesting that the observed large modifications of magnetization properties are attributed to the significant change in the Curie temperature, which is induced by a large amount of carrier density control due to the formation of the EDL. © 2012 American Institute of Physics.

  186. A Content Adddressable Memory Using Three-Terminal Magnetic Domain Wall Motion Cells 招待有り 査読有り

    R. Nebashi, N. Sakimura, Y Tsuji, S. Fukami, H. Honjo, S. Saito, S.Miura, N.Ishiwata, K. kinoshita, T. Hanyu, T. Endoh, N. Kasai, H. Ohno, T. Sugibayashi

    The 2nd CSIS International Symposium on Spintronics-based VLSIs F7 24-24 2012年2月2日

  187. Effect of current on domain wall depinning field in Co/Ni nanowire 査読有り

    Ryo Hiramatsu, Kouta Kondou, Tomohiro Koyama, Yoko Yoshimura, Daichi Chiba, Shunsuke Fukami, Nobuyuki Ishiwata, Teruo Ono

    Japanese Journal of Applied Physics 51 (2 PART 1) 028005 2012年2月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/JJAP.51.028005  

    ISSN:0021-4922

    eISSN:1347-4065

    詳細を見る 詳細を閉じる

    We have investigated the effect of dc current on magnetic domain wall (DW) depinning fields in a perpendicularly magnetized Co/Ni nanowire by utilizing the giant magnetoresistance (GMR) effect. It was found that the current assisted (prevented) the domain wall depinning when the electron flow was parallel (antiparallel) to the DW depinning direction. The depinning field was found to exhibit a linear dependence on the dc current density, from which the efficiency of the effective field was estimated to be -1.5 × 10 Tm /A. © 2012 The Japan Society of Applied Physics. -14 2

  188. Domain wall dynamics driven by spin transfer torque and the spinorbit field 国際誌 査読有り

    Masamitsu Hayashi, Yoshinobu Nakatani, Shunsuke Fukami, Michihiko Yamanouchi, Seiji Mitani, Hideo Ohno

    Journal of Physics Condensed Matter 24 (2) 024221-024221 2012年1月18日

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/0953-8984/24/2/024221  

    ISSN:0953-8984

    eISSN:1361-648X

    詳細を見る 詳細を閉じる

    We have studied current-driven dynamics of domain walls when an in-plane magnetic field is present in perpendicularly magnetized nanowires using an analytical model and micromagnetic simulations. We model an experimentally studied system, ultrathin magnetic nanowires with perpendicular anisotropy, where an effective in-plane magnetic field is developed when current is passed along the nanowire due to the Rashba-like spinorbit coupling. Using a one-dimensional model of a domain wall together with micromagnetic simulations, we show that the existence of such in-plane magnetic fields can either lower or raise the threshold current needed to cause domain wall motion. In the presence of the in-plane field, the threshold current differs for positive and negative currents for a given wall chirality, and the wall motion becomes sensitive to out-of-plane magnetic fields. We show that large non-adiabatic spin torque can counteract the effect of the in-plane field.

  189. High-speed simulator including accurate MTJ models for spintronics integrated circuit design 査読有り

    Noboru Sakimura, Ryusuke Nebashi, Yukihide Tsuji, Hiroaki Honjo, Tadahiko Sugibayashi, Hiroki Koike, Takashi Ohsawa, Shunsuke Fukami, Takahiro Hanyu, Hideo Ohno, Tetsuo Endoh

    ISCAS 2012 - 2012 IEEE International Symposium on Circuits and Systems 1971-1974 2012年

    出版者・発行元:IEEE

    DOI: 10.1109/ISCAS.2012.6271663  

    ISSN:0271-4302

    詳細を見る 詳細を閉じる

    An extremely practical simulation program with integrated circuits emphasis (SPICE) incorporating model parameters of magnetic tunnel junction (MTJ) was developed. The simulator provides reliable simulation results in spintronics circuit design because it can accurately calculate various MTJ characteristics that actual devices have, that considerably influence the operation margin and power dissipation. It can also accelerate the simulation speed, which makes it possible to simulate three times or more large-scale circuits than when a conventional macro-model is used. © 2012 IEEE.

  190. Spintronics primitive gate with high error correction efficiency 6(P <inf>error</inf>) <sup>2</sup> for logic-in memory architecture 査読有り

    Y. Tsuji, R. Nebashi, N. Sakimura, A. Morioka, H. Honjo, K. Tokutome, S. Miura, T. Suzuki, S. Fukami, K. Kinoshita, T. Hanyu, T. Endoh, N. Kasai, H. Ohno, T. Sugibayashi

    Digest of Technical Papers - Symposium on VLSI Technology 63-64 2012年

    DOI: 10.1109/VLSIT.2012.6242462  

    ISSN:0743-1562

    詳細を見る 詳細を閉じる

    A spintronics primitive gate with redundancy was designed using domain wall motion (DWM) cells, and the data-missing rate was drastically improved to ∼ 6 (P ) when the error rate per DWM cell was P . All the DWM cells aligned in series were written simultaneously, which suppressed the increase in power consumption when writing. Application of 4-terminal DWM cells with physically separated current paths for writing and reading saved extra path transistors for redundancy and there were no area overheads. © 2012 IEEE. error error 2

  191. High-speed and reliable domain wall motion device: Material design for embedded memory and logic application 査読有り

    S. Fukami, M. Yamanouchi, T. Koyama, K. Ueda, Y. Yoshimura, K. J. Kim, D. Chiba, H. Honjo, N. Sakimura, R. Nebashi, Y. Kato, Y. Tsuji, A. Morioka, K. Kinoshita, S. Miura, T. Suzuki, H. Tanigawa, S. Ikeda, T. Sugibayashi, N. Kasai, T. Ono, H. Ohno

    Digest of Technical Papers - Symposium on VLSI Technology 61-62 2012年

    DOI: 10.1109/VLSIT.2012.6242461  

    ISSN:0743-1562

    詳細を見る 詳細を閉じる

    High-speed capability and excellent reliability of a magnetic domain wall (DW) motion device required for embedded memory and logic-in-memory applications were achieved by optimizing the film stack structure of Co/Ni wire. Low-current with high-speed writing, high heat resistance, low error rate, wide operation range for temperature and magnetic field, high retention, and high endurance features were confirmed. © 2012 IEEE.

  192. Electric-field control of magnetic domain-wall velocity in ultrathin cobalt with perpendicular magnetization 査読有り

    D. Chiba, M. Kawaguchi, S. Fukami, N. Ishiwata, K. Shimamura, K. Kobayashi, T. Ono

    Nature Communications 3 888 2012年

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/ncomms1888  

    ISSN:2041-1723

    eISSN:2041-1723

    詳細を見る 詳細を閉じる

    Controlling the displacement of a magnetic domain wall is potentially useful for information processing in magnetic non-volatile memories and logic devices. A magnetic domain wall can be moved by applying an external magnetic field and/or electric current, and its velocity depends on their magnitudes. Here we show that the applying an electric field can change the velocity of a magnetic domain wall significantly. A field-effect device, consisting of a top-gate electrode, a dielectric insulator layer, and a wire-shaped ferromagnetic Co/Pt thin layer with perpendicular anisotropy, was used to observe it in a finite magnetic field. We found that the application of the electric fields in the range of ± 2 - 3 MV cm can change the magnetic domain wall velocity in its creep regime (10 - 10 ms ) by more than an order of magnitude. This significant change is due to electrical modulation of the energy barrier for the magnetic domain wall motion. © 2012 Macmillan Publishers Limited. All rights reserved. 1 6 3 1

  193. Scalability prospect of three-terminal magnetic domain-wall motion device 査読有り

    Shunsuke Fukami, Nobuyuki Ishiwata, Naoki Kasai, Michihiko Yamanouchi, Hideo Sato, Shoji Ikeda, Hideo Ohno

    IEEE Transactions on Magnetics 48 (7) 2152-2157 2012年

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2012.2187792  

    ISSN:0018-9464

    eISSN:1941-0069

    詳細を見る 詳細を閉じる

    We studied a scaling property of a three-terminal domain wall (DW)-motion device, which is one of the promising candidates for future low-power nonvolatile memory and logic-in-memory architecture. Using several assumptions, we derived the scaling factor of the switching current, switching time, resistance of the write-current path, and data storage stability. We also quantitatively evaluated the variation of these parameters with the device size. It was found that the switching current and time decrease almost linearly with the device size, while the variation of the resistance of the write-current path is negligible. The switching current and time for 32-nm-wide device are less than 100 μA and 2 ns, respectively. A required critical field which assures a sufficient thermal stability of stored data was calculated for each generation. Furthermore, future issues and intrinsic limiter for the size reduction were discussed. © 2012 IEEE.

  194. Electrical control of the ferromagnetic phase transition in cobalt at room temperature 査読有り

    D. Chiba, S. Fukami, K. Shimamura, N. Ishiwata, K. Kobayashi, T. Ono

    Nature Materials 10 (11) 853-856 2011年11月

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/nmat3130  

    ISSN:1476-1122

    eISSN:1476-4660

    詳細を見る 詳細を閉じる

    Electrical control of magnetic properties is crucial for device applicationsin the field of spintronics. Although the magnetic coercivity or anisotropy has been successfully controlled electrically in metals as well as in semiconductors, the electrical control of Curie temperature has been realized only in semiconductors at low temperature. Here, we demonstrate the room-temperature electrical control of the ferromagnetic phase transition in cobalt, one of the most representative transition-metal ferromagnets. Solid-state field effect devices consisting of a ultrathin cobalt film covered by a dielectric layer and a gate electrode were fabricated. We prove that the Curie temperature of cobalt can be changed by up to 12K by applying a gate electric field of about 2MVcm-1. The two-dimensionality of the cobalt film may be relevant to our observations. The demonstrated electric field effect in the ferromagnetic metal at room temperature is a significant step towards realizing future low-power magnetic applications. © 2011 Macmillan Publishers Limited. All rights reserved.

  195. Electrical control of the ferromagnetic phase transition in cobalt at room temperature 査読有り

    D. Chiba, S. Fukami, K. Shimamura, N. Ishiwata, K. Kobayashi, T. Ono

    NATURE MATERIALS 10 (11) 853-856 2011年11月

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/NMAT3130  

    ISSN:1476-1122

    詳細を見る 詳細を閉じる

    Electrical control of magnetic properties is crucial for device applications in the field of spintronics(1-20). Although the magnetic coercivity or anisotropy has been successfully controlled electrically in metals(9,15,17) as well as in semiconductors(6,10,11,13), the electrical control of Curie temperature has been realized only in semiconductors at low temperature(4,5,8). Here, we demonstrate the room-temperature electrical control of the ferromagnetic phase transition in cobalt, one of the most representative transition-metal ferromagnets. Solid-state field effect devices consisting of a ultrathin cobalt film(21,22) covered by a dielectric layer and a gate electrode were fabricated. We prove that the Curie temperature of cobalt can be changed by up to 12 K by applying a gate electric field of about +/- 2 MV cm(-1). The two-dimensionality of the cobalt film may be relevant to our observations. The demonstrated electric field effect in the ferromagnetic metal at room temperature is a significant step towards realizing future low-power magnetic applications.

  196. Wire width dependence of threshold current density for domain wall motion in Co/Ni nanowires 査読有り

    Tomohiro Koyama, Daichi Chiba, Kohei Ueda, Hironobu Tanigawa, Shunsuke Fukami, Tetsuhiro Suzuki, Norikazu Ohshima, Nobuyuki Ishiwata, Yoshinobu Nakatani, Teruo Ono

    IEEE Transactions on Magnetics 47 (10) 3089-3091 2011年10月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2011.2157308  

    ISSN:0018-9464

    詳細を見る 詳細を閉じる

    The authors have investigated wire width dependence of threshold current density for current-induced magnetic domain wall (DW) motion in perpendicularly magnetized Co/Ni nanowires. Threshold current density decreased with reducing the wire width, and the lowest threshold value of 1.6× 10 A/m was observed at the narrowest width of 36 nm. The micromagnetic simulation shows that the observed width dependence of threshold current density can be understood by the adiabatic spin transfer model. © 2011 IEEE. 11 2

  197. Electrical investigation of notch width dependence of domain wall structure in Co/Ni Nanowires 査読有り

    Kouta Kondou, Ryo Hiramatsu, Tomohiro Koyama, Yoshinobu Nakatani, Daichi Chiba, Shunsuke Fukami, Nobuyuki Ishiwata, Teruo Ono

    Japanese Journal of Applied Physics 50 (7 PART 1) 073002 2011年7月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/JJAP.50.073002  

    ISSN:0021-4922

    eISSN:1347-4065

    詳細を見る 詳細を閉じる

    We have investigated the notch width dependence of the domain wall structure by measuring the wall resistances in Co/Ni nanowires with perpendicular magnetization. Wall resistance was abruptly increased below a notch width of 43 nm. By comparing the experimental results with theoretical calculations of wall resistance and the micromagnetic simulation of wall energy, this increase in wall resistance was found to be caused by the change in the wall structure from the Bloch to Néel wall caused by the decreased notch width. © 2011 The Japan Society of Applied Physics.

  198. Current-induced magnetic domain wall motion in Co/Ni nanowire at low temperature 査読有り

    Kohei Ueda, Tomohiro Koyama, Daichi Chiba, Kazutoshi Shimamura, Hironobu Tanigawa, Shunsuke Fukami, Tetsuhiro Suzuki, Norikazu Ohshima, Nobuyuki Ishiwata, Yoshinobu Nakatani, Teruo Ono

    Applied Physics Express 4 (6) 063003 2011年6月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/APEX.4.063003  

    ISSN:1882-0778

    eISSN:1882-0786

    詳細を見る 詳細を閉じる

    Magnetic domain wall (DW) motion induced by currents in a perpendicularly magnetized Co/Ni nanowire has been investigated both at room temperature and low temperature. The threshold current density was almost independent of temperature, although the external magnetic field to depin a DW was doubled at low temperature. The result is consistent with the theory based on the adiabatic spin transfer model. © 2011 The Japan Society of Applied Physics.

  199. Magnetic field insensitivity of magnetic domain wall velocity induced by electrical current in Co/Ni nanowire 査読有り

    T. Koyama, D. Chiba, K. Ueda, H. Tanigawa, S. Fukami, T. Suzuki, N. Ohshima, N. Ishiwata, Y. Nakatani, T. Ono

    Applied Physics Letters 98 (19) 192509 2011年5月9日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3590713  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    We have investigated the velocity of magnetic domain wall (DW) motion induced by electric currents in a Co/Ni nanowire with a perpendicular magnetic anisotropy. The DW velocity increased as current density increased and the maximum velocity of 60 m/s was observed. Furthermore, the DW velocity was found to be almost independent of external perpendicular magnetic fields in the range of -50 to +50Oe. The mechanism of the observed field insensitivity of the current induced DW motion is also discussed. © 2011 American Institute of Physics.

  200. Current-induced effective field in perpendicularly magnetized Ta/CoFeB/MgO wire 査読有り

    T. Suzuki, S. Fukami, N. Ishiwata, M. Yamanouchi, S. Ikeda, N. Kasai, H. Ohno

    Applied Physics Letters 98 (14) 142505 2011年4月

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3579155  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    The current-induced effective field in perpendicularly magnetized Ta/CoFeB/MgO wire was investigated. A threshold field decrease of 6.4 kOe/mA was observed by measuring the threshold field of Hall resistance versus the magnetic field curve with various bias currents. The decrease was probably caused by the in-plane effective field, mainly due to the Rashba effect. The effective field of the Ta/CoFeB/MgO wire was smaller and opposite in direction compared to that of Pt/Co/AlO previously reported. © 2011 American Institute of Physics. x

  201. Observation of the intrinsic pinning of a magnetic domain wall in a ferromagnetic nanowire 査読有り

    T. Koyama, D. Chiba, K. Ueda, K. Kondou, H. Tanigawa, S. Fukami, T. Suzuki, N. Ohshima, N. Ishiwata, Y. Nakatani, K. Kobayashi, T. Ono

    Nature Materials 10 (3) 194-197 2011年3月

    出版者・発行元:NATURE PUBLISHING GROUP

    DOI: 10.1038/nmat2961  

    ISSN:1476-1122

    eISSN:1476-4660

    詳細を見る 詳細を閉じる

    The spin transfer torque is essential for electrical magnetization switching. When a magnetic domain wall is driven by an electric current through an adiabatic spin torque, the theory predicts a threshold current even for a perfect wire without any extrinsic pinning. The experimental confirmation of this -intrinsic pinningg-however, has long been missing. Here, we give evidence that this intrinsic pinning determines the threshold, and thus that the adiabatic spin torque dominates the domain wall motion in a perpendicularly magnetized Co/Ni nanowire. The intrinsic nature manifests itself both in the field-independent threshold current and in the presence of its minimum on tuning the wire width. The demonstrated domain wall motion purely due to the adiabatic spin torque will serve to achieve robust operation and low energy consumption in spintronic devices. © 2011 Macmillan Publishers Limited. All rights reserved.

  202. Current-induced domain wall motion in perpendicularly magnetized CoFeB nanowire 査読有り

    S. Fukami, T. Suzuki, Y. Nakatani, N. Ishiwata, M. Yamanouchi, S. Ikeda, N. Kasai, H. Ohno

    Applied Physics Letters 98 (8) 082504 2011年2月21日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3558917  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    Current-induced domain wall motion in perpendicularly magnetized CoFeB nanowires with a stack structure of Ta(1.0 nm)/CoFeB(1.2 nm)/MgO(2.0 nm)/Ta(1.0 nm) was investigated. Domain wall motion driven by adiabatic spin-transfer torque was observed at a current of about 74 μA, corresponding to a current density of 6.2× 10 A/ cm . The obtained results were compared with those of a micromagnetic simulation and the spin polarization of the CoFeB was estimated to be 0.72. © 2011 American Institute of Physics. 7 2

  203. Three-terminal domain-wall cell architectures 査読有り

    N. Ishiwata, S. Fukami, S. Saitho, R. Nebashi, N. Sakimura, H. Honjo, S. Miura, T. Sugibayashi, Y. Thuji, M. Murahata, H. Ohno, T. Endoh, T. Hanyu, N. Kasai

    International Magnetics Conference 2011 abstract 2011年

  204. Current-induced Domain Wall Motion MRAM 査読有り

    N. Ishiwata, S. Fukami, T. Suzuki, K. Nagahara, N. Ohshima, S. Saito, R.Nebashi, N.Sakimura, H. Honjo, K. Mori, T. Igarashi, H. Tanigawa, S. Miura, T. Sugibayashi

    Int Magnetics Conf/Int Conf on Magnetism & Magnetic Materials Abstract 2011年

  205. A 600MHz MTJ-based nonvolatile latch making use of incubation time in MTJ switching 査読有り

    T. Endoh, S. Togashi, F. Iga, Y. Yoshida, T. Ohsawa, H. Koike, S. Fukami, S. Ikeda, N. Kasai, N. Sakimura, T. Hanyu, H. Ohno

    Technical Digest - International Electron Devices Meeting, IEDM 6131487 2011年

    出版者・発行元:IEEE

    DOI: 10.1109/IEDM.2011.6131487  

    ISSN:0163-1918

    詳細を見る 詳細を閉じる

    The incubation (transit) time of the perpendicular magnetic tunnel junction (MTJ) is found shorter (longer) than the in-plane MTJ. By making use of the incubation time, a new concept is proposed for MTJ/CMOS hybrid circuits that operate as fast as CMOS circuits without operation power overhead and with negligible MTJ switching error. A nonvolatile latch based on the concept is fabricated in 90nm technology to demonstrate 600MHz stable operation. © 2011 IEEE.

  206. Fully parallel 6T-2MTJ nonvolatile TCAM with single-transistor-based self match-line discharge control 査読有り

    Shoun Matsunaga, Akira Katsumata, Masanori Natsui, Shunsuke Fukami, Tetsuo Endoh, Hideo Ohno, Takahiro Hanyu

    IEEE Symposium on VLSI Circuits, Digest of Technical Papers 298-299 2011年

    詳細を見る 詳細を閉じる

    A six-MOS-transistor/two-MTJ-device (6T-2MTJ)-based cell circuit with an autonomous leakage-current control mechanism is proposed and fabricated for a fully parallel nonvolatile TCAM. A diode-connected nMOS transistor is inserted into each cell for match-line discharge control, which enables bit-parallel equality-search operation more than 144 bits. Since each match line is divided into three segments, the activity rate of cells is reduced to 2.8%. This almost eliminates leakage power while maintaining comparable search energy of 1.04 fJ/bit/search in comparison with a CMOS-based TCAM. © 2011 JSAP (Japan Society of Applied Physi.

  207. A content addressable memory using magnetic domain wall motion cells 査読有り

    R. Nebashi, N. Sakimura, Y. Tsuji, S. Fukami, H. Honjo, S. Saito, S. Miura, N. Ishiwata, K. Kinoshita, T. Hanyu, T. Endoh, N. Kasai, H. Ohno, T. Sugibayashi

    IEEE Symposium on VLSI Circuits, Digest of Technical Papers 300-301 2011年

    詳細を見る 詳細を閉じる

    A 5-ns search operation of a spintronic content addressable memory (Spin-CAM) was demonstrated, and the speed was the fastest to date. The CAM macro, with a capacity of 16 kb, was fabricated using 90-nm CMOS and domain wall (DW) motion processes. The operating speed was comparable to that of SRAM-based CAM. We also propose a CAM which has multiple contexts by improving the CAM cell circuit to enhance the SoC's performance. The estimated cell area is 3.5 μm , which is less than that of an SRAM-based CAM cell, when a four-context CAM is designed. © 2011 JSAP (Japan Society of Applied Physi. 2

  208. Current-induced domain wall motion in Co/Ni nano-wires with different Co and Ni thicknesses 査読有り

    K. Ueda, D. Chiba, T. Koyama, G. Yamada, H. Tanigawa, S. Fukami, T. Suzuki, N. Ohshima, N. Ishiwata, Y. Nakatani, T. Ono

    Journal of Physics: Conference Series 266 (1) 012110 2011年

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/1742-6596/266/1/012110  

    ISSN:1742-6588

    eISSN:1742-6596

    詳細を見る 詳細を閉じる

    The authors have investigated magnetic domain wall motion induced by electric currents in ferromagnetic nano-wires made of Co/Ni multilayers. The thicknesses of Co and Ni layers were changed, whereas the numbers of layer stacks of Co and Ni were the same in all samples. The sample with thinner total Co/Ni thickness showed the lower threshold current density for the domain wall motion as an overall trend, which is qualitatively in agreement with the expectation by the theory based on the adiabatic spin-transfer model. The lowest threshold current density was 2.9×10 A/m obtained in the sample with the total Co/Ni thickness of 3.4 nm and the wire width of 110 nm. © Published under licence by IOP Publishing Ltd. 11 2

  209. Effect of device temperature on domain wall motion in a perpendicularly magnetized Co/Ni wire 査読有り

    Hironobu Tanigawa, Katsumi Suemitsu, Shunsuke Fukami, Norikazu Ohshima, Tetsuhiro Suzuki, Eiji Kariyada, Nobuyuki Ishiwata

    Applied Physics Express 4 (1) 013007 2011年1月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/APEX.4.013007  

    ISSN:1882-0778

    eISSN:1882-0786

    詳細を見る 詳細を閉じる

    This paper describes experimental results obtained from measuring the dependence of device temperature on the current for domain wall motion in a Co/Ni wire having perpendicular magnetic anisotropy. Devices with different insulating layer thicknesses were prepared in order to control the device temperature. A stable domain wall motion was observed up to the temperature at which perpendicular magnetic anisotropy vanishes. Moreover, the current required for domain wall motion was independent of the device temperature. © 2011 The Japan Society of Applied Physics.

  210. Large thermal stability independent of critical current of domain wall motion in Co/Ni nanowires with step pinning sites 査読有り

    Shunsuke Fukami, Tetsuhiro Suzuki, Kiyokazu Nagahara, Norikazu Ohshima, Nobuyuki Ishiwata

    Journal of Applied Physics 108 (11) 113914 2010年12月1日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3518046  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    The relation between critical current, critical field, and thermal stability of domain wall (DW) trapped at step pinning sites was studied using Co/Ni nanowires with perpendicular magnetic anisotropy (PMA). A sharp step structure was fabricated, which increased the critical field of DW motion, while the critical current was independent of the critical field. Also, the derived thermal stability (ΔE/ k T) for the step samples was much more than 60. These results indicate that the DW motion in PMA nanowires has potential for memory devices with both a small driving current and large thermal stability. © 2010 American Institute of Physics. B

  211. Stack structure dependence of Co/Ni multilayer for current-induced domain wall motion 査読有り

    Shunsuke Fukami, Tetsuhiro Suzuki, Hironobu Tanigawa, Norikazu Ohshima, Nobuyuki Ishiwata

    Applied Physics Express 3 (11) 113002 2010年11月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1143/APEX.3.113002  

    ISSN:1882-0778

    eISSN:1882-0786

    詳細を見る 詳細を閉じる

    We developed a film stack structure of Co/Ni with perpendicular magnetic anisotropy (PMA), which is suitable for current-induced domain wall (DW) motion. A Ta/Pt underlayer effectively provided a sufficiently large PMA to achieve the DW motion driven by a small current. The critical current density ( j ) had a minimum value at a Pt underlayer thickness (t ) of 2.4nm and was insensitive to cap layer thickness (t ). The dependence of j on t and t can be accounted for in terms of the effective spin polarization. © 2010 The Japan Society of Applied Physics. c UL cap c UL cap

  212. Control of multiple magnetic domain walls by current in a Co/Ni nano-wire 査読有り

    Daichi Chiba, Gen Yamada, Tomohiro Koyama, Kohei Ueda, Hironobu Tanigawa, Shunsuke Fukami, Tetsuhiro Suzuki, Norikazu Ohshima, Nobuyuki Ishiwata, Yoshinobu Nakatani, Teruo Ono

    Applied Physics Express 3 (7) 073004 2010年7月

    出版者・発行元:JAPAN SOC APPLIED PHYSICS

    DOI: 10.1143/APEX.3.073004  

    ISSN:1882-0778

    eISSN:1882-0786

    詳細を見る 詳細を閉じる

    All-electrical control and local detection of multiple magnetic domain walls in perpendicularly magnetized Co/Ni nano-wires were demonstrated. A series of domain walls was reproducibly shifted in the same direction by the current, keeping the distance between the walls almost the same. Furthermore, the walls can be shifted back and forth depending on the direction of the pulsed currents. © 2010 The Japan Society of Applied Physics.

  213. Magnetic configuration of submicron-sized magnetic patterns in domain wall motion memory 査読有り

    Norikazu Ohshima, Hideaki Numata, Shunsuke Fukami, Kiyokazu Nagahara, Tetsuhiro Suzuki, Nobuyuki Ishiwata, Keiki Fukumoto, Toyohiko Kinoshita, Teruo Ono

    Journal of Applied Physics 107 (10) 103912 2010年5月15日

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3427555  

    ISSN:0021-8979

    eISSN:1089-7550

    詳細を見る 詳細を閉じる

    We observed magnetic configuration and its change by external magnetic fields in submicron-sized U- and H-shaped NiFe patterns with an x-ray magnetic circular dichroism photoemission electron microscope. The microscope images showed the formation of a single domain wall (DW) with transverse structure at one corner of the U- and H-shaped patterns by applying the magnetic field from the oblique direction. By applying the magnetic field from the direction parallel to a horizontal bar in the patterns, the magnetic configuration in the U-shaped pattern was changed and four patterns were formed: (1) the DW moved from one trap site to another, (2) the DW moved beyond the trap site and formed a single domain, (3) the DW moved and stopped between the trap sites, and (4) the DW remained at the initial position. Only pattern (1) showed reversible DW motion, although pattern (2) was predominantly formed. In contrast, the magnetization configurations showed pattern (1), and reversible DW motion was observed for more than 80% of the H-shaped patterns. Micromagnetic simulation revealed that the DW in the U-shaped pattern was not sufficiently fixed at the corner and easily moved and vanished at the edge of the patterns because the magnetization in the two parallel bars rotated with a magnetic field. The DW was trapped with sufficient strength at the corner, and DW motion occurred only between the trap sites for the H-shaped patterns. The DW motion process was observed with an in situ magnetic field using the x-ray magnetic circular dichroism photoemission electron microscope and the process could be optimized by controlling the pattern shape. © 2010 American Institute of Physics.

  214. Current Status and Future Challemge of Embedded High-speed MRAM 査読有り

    S. Fukami, T. Suzuki, K. Nagahara, N. Ohshima, S. Saitoh, R. Nebashi, N. Sakimura, H. Honjo, K. Mori, E. Kariyada, Y. Kato, K. Suemitsu, H. Tanigawa, K. Kinoshita, S. Miura, N. Ishiwata, T. Sugibayashi

    International Conference on Solid State Devices and Materials Proceedings 2010年

  215. Evaluation of scalability for current-driven domain wall motion in a Co/Ni multilayer strip for memory applications 査読有り

    Tetsuhiro Suzuki, Shunsuke Fukami, Kiyokazu Nagahara, Norikazu Ohshima, Nobuyuki Ishiwata

    IEEE Transactions on Magnetics 45 (10) 3776-3779 2009年10月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2009.2023069  

    ISSN:0018-9464

    eISSN:1941-0069

    詳細を見る 詳細を閉じる

    We study current-driven domain-wall (DW) motion and thermal stability of Co/Ni strips with DWs at the step boundaries by detecting DW resistance. The depinning current is around 0.5 mA, while the pinning field is 300 Oe, which corresponds to the thermal stability factor of 54 estimated by self-distribution of the pinning field. The depinning current decreases as the strip width decreases and does not strongly depend on the pinning field. On the other hand, the thermal stability factor increases as the pinning field increases. Therefore, an even lower current with sufficient thermal stability can be achieved by decreasing the strip width and increasing the pinning field. © 2009 IEEE.

  216. Domain wall motion induced by electric current in a perpendicularly magnetized Co/Ni nano-wire 査読有り

    Hironobu Tanigawa, Tomohiro Koyama, Gen Yamada, Daichi Chiba, Shinya Kasai, Shunsuke Fukami, Tetsuhiro Suzuki, Norikazu Ohshima, Nobuyuki Ishiwata, Yoshinobu Nakatani, Teruo Ono

    Applied Physics Express 2 (5) 053002 2009年5月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1143/APEX.2.053002  

    ISSN:1882-0778

    eISSN:1882-0786

    詳細を見る 詳細を閉じる

    The authors show experimental results on domain wall motion induced by electric current in a Co/Ni nano-wire with perpendicular magnetic anisotropy. The motion was detected electrically by using the anomalous Hall effect. Threshold current density for the domain wall motion was found to decrease with decreasing the wire width, where the minimum threshold current density of approximately 5 × 10 A/m was observed for the wire width of 70 nm. © 2009 The Japan Society of Applied Physics. 11 2

  217. High-speed Magnetic Memory based on Spin-Torque Domain Wall Motion 査読有り

    N. Ishiwata, S. Fukami, T.Suzuki, K. Nagahara, N. Ohshima, H. Honjo, K. Mori, T. Igarashi, S. Miura, T. Sugibayashi, K. Ozaki, S. Saito, R. Nebashi, N. Sakimura

    Int Conf on Solid State Devices & Materials Proceedings 2009年

  218. Relation between critical current of domain wall motion and wire dimension in perpendicularly magnetized Co/Ni nanowires 査読有り

    S. Fukami, Y. Nakatani, T. Suzuki, K. Nagahara, N. Ohshima, N. Ishiwata

    Applied Physics Letters 95 (23) 232504 2009年

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3271827  

    ISSN:0003-6951

    詳細を見る 詳細を閉じる

    We investigated the relation between critical current of domain wall motion and wire dimension by using perpendicularly magnetized Co/Ni nanowires with different widths and thicknesses. The critical current, I , became less than 0.2 mA when w<100 nm, suggesting that magnetic random access memory with domain wall motion can replace conventional embedded memories. In addition, in agreement with theory, the critical current density, j , decreased as wire width decreased and became much less than 5× 10 A/ cm when w<100 nm. We also performed a micromagnetic simulation and obtained good agreement between the experiment and simulation, although a few discrepancies were found. © 2009 American Institute of Physics. c c 7 2

  219. Low-current perpendicular domain wall motion cell for scalable high-speed MRAM 査読有り

    S. Fukami, T. Suzuki, K. Nagahara, N. Ohshima, Y. Ozaki, S. Saito, R. Nebashi, N. Sakimura, H. Honjo, K. Mori, C. Igarashi, S. Miura, N. Ishiwata, T. Sugibayashi

    Digest of Technical Papers - Symposium on VLSI Technology 230-231 2009年

    出版者・発行元:JAPAN SOCIETY APPLIED PHYSICS

    ISSN:0743-1562

    詳細を見る 詳細を閉じる

    We have developed a new magnetic random access memory with current-induced domain wall (DW) motion (DW-motion MRAM). We confirmed its potential of 0.1-mA and 2-ns writing with sufficient thermal stability. The obtained properties indicate that this MRAM can replace conventional high-speed embedded memories.

  220. A 90nm 12ns 32Mb 2T1MTJ MRAM 査読有り

    R. Nebashi, N. Sakimura, H. Honjo, S. Saito, Y. Ito, S. Miura, Y. Kato, K. Mori, Y. Ozaki, Y. Kobayashi, N. Ohshima, K. Kinoshita, T. Suzuki, K. Nagahara, N. Ishiwata, K. Suemitsu, S. Fukami, H. Hada, T. Sugibayashi, N. Kasai

    Digest of Technical Papers - IEEE International Solid-State Circuits Conference 462-464 2009年

    DOI: 10.1109/ISSCC.2009.4977508  

    ISSN:0193-6530

  221. Performance of shape-varying magnetic tunneling junction for high-speed magnetic random access memory cells 査読有り

    H. Honjo, S. Fukami, R. Nebashi, T. Suzuki, N. Ishiwata, S. Miura, T. Sugibayashi

    Journal of Applied Physics 105 (7) 07C921 2009年

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3062825  

    ISSN:0021-8979

    詳細を見る 詳細を閉じる

    We have developed a shape-varying magnetic tunneling junction (MTJ) (SVM) which has a high MR ratio and low write current for use in high-speed magnetic random access memory (MRAM) cells. Combining NiFe that has low anisotropy to CoFeB which has high anisotropy through the nonmagnetic layer by interlayer exchange coupling (synthetic ferromagnetic coupling free layer: SFF), the anisotropy of SFF was reduced much more than that of CoFeB, and the MR ratio was improved much more than that of NiFe. The switching magnetic field (Hsw) of SFF was reduced as the thickness of NiFe increased. The Hsw of SFF for 0.24×0.48 μ m2 MTJ was 30 Oe when the thickness of CoFeB was 1.5 nm and that of NiFe was 3.0 nm. Furthermore Hsw was reduced to 18 Oe by varying the shape of the MTJ of NiFe to 0.48×0.48 μ m2; the shape of the MTJ of CoFeB was not changed (0.24×0.48 μ m2). Combining the SVM and a write-line-inserted structure, we obtained a write current of 0.9 mA and an MR ratio of 140%. The Hsw was 40 Oe and its thermal stability factor was 82. These properties are sufficient for operating MRAMs over 500 MHz. © 2009 American Institute of Physics.

  222. Intrinsic threshold current density of domain wall motion in nanostrips with perpendicular magnetic anisotropy for use in low-write-current MRAMs 査読有り

    Shunsuke Fukami, Tetsuhiro Suzuki, Norikazu Ohshima, Kiyokazu Nagahara, Nobuyuki Ishiwata

    IEEE Transactions on Magnetics 44 (11 PART 2) 2539-2542 2008年11月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2008.2002370  

    ISSN:0018-9464

    詳細を見る 詳細を閉じる

    In this paper, we have calculated the intrinsic threshold current density of domain wall (DW) motion in nanostrips with perpendicular magnetic anisotropy (PMA) and have estimated writing properties of magnetic random access memories (MRAMs) with DW motion. Carrying out a micromagnetic simulation, we revealed that the intrinsic threshold current density decreases with decreases in the strip thickness, width, and magnetization, whereas it did not depend significantly on magnetocrystalline anisotropy and exchange stiffness. These results showed good agreement with one-dimensional (1-D) analysis. We also found that current-induced DW motion in PMA strips may have potential for use in low-write-current MRAMs. For a width of less than roughly 100 nm, comparable properties to those of existing memories can be obtained. © 2008 IEEE.

  223. Current-driven domain wall motion, nucleation, and propagation in a Co/Pt multi-layer strip with a stepped structure 査読有り

    Tetsuhiro Suzuki, Shunsuke Fukami, Kiyokazu Nagahara, Norikazu Ohshima, Nobuyuki Ishiwata

    IEEE Transactions on Magnetics 44 (11 PART 2) 2535-2538 2008年11月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2008.2002486  

    ISSN:0018-9464

    eISSN:1941-0069

    詳細を見る 詳細を閉じる

    We have proposed detecting a domain wall behavior in a strip with perpendicular magnetic anisotropy by measuring both extraordinary Hall effect and domain wall resistance with unique placement of three via contacts. By using this detecting technique, we have confirmed that the domain wall can be initialized at the boundary of the stepped structure of a Co/Pt multilayer strip. We have observed nucleation independent of the current direction and the propagation depending on it. We could not find any domain wall motion by spin-transfer torque from the boundary until 1.8 × 10 A/m , probably because of the smaller polarization and/or the larger damping constant of the Co/Pt multilayer. © 2008 IEEE. 12 2

  224. Control of domain wall position by electrical current in structured Co/Ni wire with perpendicular magnetic anisotropy 査読有り

    Tomohiro Koyama, Gen Yamada, Hironobu Tanigawa, Shinya Kasai, Norikazu Ohshima, Shunsuke Fukami, Nobuyuki Ishiwata, Yoshinobu Nakatani, Teruo Ono

    Applied Physics Express 1 (10) 1013031-1013033 2008年10月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1143/APEX.1.101303  

    ISSN:1882-0778

    eISSN:1882-0786

    詳細を見る 詳細を閉じる

    We report the direct observation of the current-driven domain wall (DW) motion by magnetic force microscopy in a structured Co/Ni wire with perpendicular magnetic anisotropy. The wire has notches to define the DW position. It is demonstrated that single current pulses can precisely control the DW position from notch to notch with high DW velocity of 40 m/s. © 2008 The Japan Society of Applied Physics.

  225. Low write-current magnetic random access memory cell with anisotropy-varied free layers 査読有り

    S. Fukami, H. Honjo, T. Suzuki, N. Ishiwata

    Journal of Applied Physics 104 (11) 113901 2008年

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.3032894  

    ISSN:0021-8979

    詳細を見る 詳細を閉じる

    We propose a magnetic random access memory (MRAM) cell that utilizes field-induced switching and is applicable to high-speed memories. The MRAM cell, called the shape-varying MRAM cell, has three free layers, each having different shapes and functions, and achieves low write-current switching with high thermal stability and high external field robustness. We show analytically that one of the layers contributes to the low write-current switching and another contributes to the thermal stability. We also show the results of a micromagnetic simulation, in which write current of <0.5 mA, write time of <2 ns, energy barrier (ΔE/ kB T) >100, and external field robustness of >32 Oe were obtained. © 2008 American Institute of Physics.

  226. Analysis of current-driven domain wall motion from pinning sites in nanostrips with perpendicular magnetic anisotropy 査読有り

    T. Suzuki, S. Fukami, N. Ohshima, K. Nagahara, N. Ishiwata

    Journal of Applied Physics 103 (11) 113913 2008年

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2938843  

    ISSN:0021-8979

    詳細を見る 詳細を閉じる

    Current-driven domain wall motion from pinning sites in nanostrips with perpendicular magnetic anisotropy is studied by using micromagnetic simulations, supported by a one-dimensional model of wall dynamics. The threshold current density of perpendicular anisotropy strips is much smaller than that of in-plane anisotropy strips, and is almost independent of the pinning potential strength. This results from the narrower domain wall width, smaller hard-axis anisotropy, and the larger ratio of the depinning field and hard-axis anisotropy. In the one-dimensional model with a zero damping constant, the threshold current density is found to be about 0.72 of the intrinsic threshold current density for a perfect strip in a strong pinning regime that corresponds to strips with perpendicular magnetic anisotropy. The fact that the threshold current density from the pinning sites is smaller than the intrinsic current density is because the effective field, equivalent to the pinning potential, enhances a breakdown in the pinning site. Moreover, in the strong pinning regime, an opposite-direction depinning hardly ever occurs after current pulse is turned off. These features of strips with perpendicular magnetic anisotropy are attractive for magnetic random access memories where the domain wall should be moved stably between the pinning sites with the small current pulse. © 2008 American Institute of Physics.

  227. Micromagnetic analysis of current driven domain wall motion in nanostrips with perpendicular magnetic anisotropy 査読有り

    S. Fukami, T. Suzuki, N. Ohshima, K. Nagahara, N. Ishiwata

    Journal of Applied Physics 103 (7) 07E718 2008年

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2830964  

    ISSN:0021-8979

    詳細を見る 詳細を閉じる

    Current driven domain wall motion in nanostrips with perpendicular magnetic anisotropy was analyzed by using micromagnetic simulation. The threshold current density of perpendicular anisotropy strips in adiabatic approximation was much smaller than that of in-plane anisotropy strips, and it reduced with thickness reduction. The differences originate from the differences in domain wall width and hard-axis anisotropy. Also, the threshold current density of perpendicular anisotropy strips required to depin from a pinning site was quite small although the threshold field of the strips was sufficiently large relative to those of in-plane anisotropy strips. © 2008 American Institute of Physics.

  228. Performance of write-line inserted magnetic tunneling junction for low-write-current magnetic random access memory cell 査読有り

    H. Honjo, R. Nebashi, T. Suzuki, S. Fukami, N. Ishiwata, T. Sugibayashi, N. Kasai

    Journal of Applied Physics 103 (7) 07A711 2008年

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2839288  

    ISSN:0021-8979

    詳細を見る 詳細を閉じる

    We have developed a write-line-inserted magnetic tunneling junction (MTJ) (WLIM) for use in low-write-current magnetoresistance random access memory (MRAM). The write current of the WLIM was reduced to 0.98 mA and its thermal stability factor was 85 for a 0.32×0.48 μ m2 MTJ. We evaluated the switching property of the WLIM in an external magnetic field (Hsw_ext) and an internal magnetic field (Hsw_int). We found that Hsw_ext was larger than Hsw_int when the aspect ratio of the MTJs was less than 1.5. Furthermore, we obtained a high write-current magnetic-field efficiency of 13.0 OemA when the aspect ratio of the MTJs was low. These properties mean that the WLIM structure has advantages for use in low-write-current MRAM. © 2008 American Institute of Physics.

  229. Reduction of critical current density for domain wall motion in U-shaped magnetic patterns 査読有り

    N. Ohshima, H. Numata, T. Suzuki, S. Fukami, K. Nagahara, N. Ishiwata

    Journal of Applied Physics 103 (7) 07D914 2008年

    出版者・発行元:AMER INST PHYSICS

    DOI: 10.1063/1.2830544  

    ISSN:0021-8979

    詳細を見る 詳細を閉じる

    The critical current density required for current-induced domain wall motion (Jc) was reduced by decreasing the magnetization (Ms) of the free layer film of a U-shaped pattern for a domain wall motion memory. The Ms was decreased by adding the nonmagnetic elements Ta and Cu to NiFe films. The Jc of the U-shaped patterns with NiFe-Ta and -Cu decreased as the proportion of Ta and Cu in the NiFe increased. The relations between Ms and Jc were examined and it was found that Jc decreased monotonically from 1.2× 1012 to 0.8× 1012 A m2 as Ms decreased from 1.0 to 0.6 T regardless of what other materials were used. It is considered that the decrease in Ms caused a decrease in the hard axis anisotropy of the pattern, and the Jc decreased as predicted by a one-dimensional model. © 2008 American Institute of Physics.

  230. Current-driven domain wall motion in CoCrPt wires with perpendicular magnetic anisotropy 査読有り

    Hironobu Tanigawa, Kouta Kondou, Tomohiro Koyama, Kunihiro Nakano, Shinya Kasai, Norikazu Ohshima, Shunsuke Fukami, Nobuyuki Ishiwata, Teruo Ono

    Applied Physics Express 1 (1) 011301 2008年1月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1143/APEX.1.011301  

    ISSN:1882-0778

    eISSN:1882-0786

    詳細を見る 詳細を閉じる

    We report the direct observation of current-driven domain wall (DW) motion in a CoCrPt wire with perpendicular magnetic anisotropy. Magnetic force microscopy showed that a single DW introduced in the wire is displaced back and forth by positive and negative pulsed current. This is the first demonstration of the current-driven DW motion in a metallic magnetic wire with perpendicular magnetic anisotropy in the absence of a magnetic field. © 2008 The Japan Society of Applied Physics.

  231. A 16-Mb toggle MRAM with burst modes 査読有り

    Tadahiko Sugibayashi, Noboru Sakimura, Takeshi Honda, Kiyokazu Nagahara, Kiyotaka Tsuji, Hideaki Numata, Sadahiko Miura, Ken Ichi Shimura, Yuko Kato, Shinsaku Saito, Yoshiyuki Fukumoto, Hiroaki Honjo, Tetsuhiro Suzuki, Katsumi Suemitsu, Tomonori Mukai, Kaoru Mori, Ryusuke Nebashi, Shunsuke Fukami, Norikazu Ohshima, Hiromitsu Hada, Nobuyuki Ishiwata, Naoki Kasai, Shuichi Tahara

    IEEE Journal of Solid-State Circuits 42 (11) 2378-2385 2007年11月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/JSSC.2007.906195  

    ISSN:0018-9200

    eISSN:1558-173X

    詳細を見る 詳細を閉じる

    This paper describes a recently developed 16-Mb toggle magnetic random access memory (MRAM). It has 100-MHz burst modes that are compatible with a pseudo-SRAM even though the toggle cell requires reading and comparing sequences in write modes. To accelerate operating clock frequency, we propose a distributed-driver wide-swing current-mirror scheme, an interleaved and pipelined memory-array group activation scheme, and a noise-insulation switch scheme. These circuit schemes compensate the toggle cell timing overhead in write modes and maintain write-current precision that is essential for the wide operational margin of MRAMs. Because toggle cells are very resistant to write disturbance errors, we designed the 16-Mb MRAM to include a toggle MRAM cell. The MRAM was fabricated with 0.13-μm CMOS and 0.24-μm MRAM processes with five metal layers. © 2007 IEEE.

  232. Reduction of writing field distribution in a magnetic random access memory with toggle switching 査読有り

    Shunsuke Fukami, Hiroaki Honjo, Tetsuhiro Suzuki, Nobuyuki Ishiwata

    IEEE Transactions on Magnetics 43 (8) 3512-3516 2007年8月

    出版者・発行元:IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC

    DOI: 10.1109/TMAG.2007.900573  

    ISSN:0018-9464

    詳細を見る 詳細を閉じる

    We have investigated the distribution of the flop field, which represents writing field in a toggle magnetic random access memory (MRAM). We analyzed the factors of the distribution by dividing them into the 45° and 135° directions in (H , H ) coordinates. We found that the distribution in the 135° direction is mainly caused by stress-induced anisotropy and can be effectively suppressed by adopting materials that maintain low magnetostriction even after the fabrication process. On the other hand, we found that the distribution in the 45° direction depends on the texture and atomic structure of the ferromagnetic layers, and that low distribution can be attained when the ferromagnetic layers are constructed from small crystalline grains or amorphous materials. We demonstrated a toggle MRAM with a distribution of the flop field only half that of the previously reported magnetic tunnel junction stack structure. © 2007 IEEE. x y

  233. Scalable cell technology utilizing domain wall motion for high-speed MRAM 査読有り

    H. Numata, T. Suzuki, N. Ohshima, S. Fukami, K. Nagahara, N. Ishiwata, N. Kasai

    Digest of Technical Papers - Symposium on VLSI Technology 232-233 2007年

    出版者・発行元:JAPAN SOCIETY APPLIED PHYSICS

    DOI: 10.1109/VLSIT.2007.4339705  

    ISSN:0743-1562

    詳細を見る 詳細を閉じる

    We propose a new MRAM cell that stores data in the form of the domain wall (DW) position. The DW is moved by the spin-polarized current that flows in the free layer. The cell was fabricated and the writing characteristics were investigated. A writing current of the cell was scalable, and the current density was reduced by using a new material. The cell is suitable for a high-speed MRAM that will compete with an eSRAM.

  234. A 16Mb toggle MRAM with burst modes 査読有り

    Tadahiko Sugibayashi, Noboru Sakimura, Takeshi Honda, Kiyokazu Nagahara, Kiyotaka Tsuji, Hideaki Numata, Sadahiko Miura, Ken Ichi Shimura, Yuko Kato, Shinsaku Saito, Yoshiyuki Fukumoto, Hiroaki Honjo, Tetsuhiro Suzuki, Katsumi Suemitsu, Tomonori Mukai, Kaoru Mori, Ryusuke Nebashi, Shunsuke Fukami, Hiromitsu Hada, Nobuyuki Ishiwata, Naoki Kasai, Shuichi Tahara

    2006 IEEE Asian Solid-State Circuits Conference, ASSCC 2006 299-302 2006年

    DOI: 10.1109/ASSCC.2006.357910  

    詳細を見る 詳細を閉じる

    We have developed a 16Mb toggle MRAM. It has some 100-MHz burst modes that are compatible with a pseudo SRAM even though the toggle cell requires reading and comparing sequences in write modes. To accelerate operating clock frequency, an interleaved and pipelined memory-array group activation scheme and a noise insulation switch scheme have been proposed. The MRAM was fabricated with a 0.13-μm CMOS and 0.24-μm MRAM process with five metal layers. © 2006 IEEE.

  235. Nanostructure of CoPtCr-SiO <inf>2</inf> granular films for magnetic recording media 査読有り

    Shunsuke Fukami, Nobuo Tanaka, Takehito Shimatsu, Osamu Kitakami

    Materials Transactions 46 (8) 1802-1806 2005年8月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.46.1802  

    ISSN:1345-9678

    eISSN:1347-5320

    詳細を見る 詳細を閉じる

    Structural properties of CoPtCr-SiO magnetic recording films grown on Ru or Pt seed layers prepared by UHV-magnetron sputtering were studied by high resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS) and energy filtered transmission electron microscopy (EFTEM). CoPtCr grown on Ru seed layers together with SiO forms a well-isolated structure composed of CoPtCr fine grains of 10nm diameter surrounded by amorphous SiO , whereas CoPtCr grown on Pt seed layers together with SiO forms a network structure composed of CoPtCr crystal of 5 nm size. These structural features made differences in their magnetic properties. The HRTEM and EFTEM studies revealed that cylindrical crystalline grains composed of CoPtCr and Ru are formed for CoPtCr-SiO /Ru samples, whereas SiO are aggregated around the boundary between relatively large Pt grains and magnetic layers without obstructing the epitaxial growth of CoPtCr on Pt, not resulting in the cylindrical CoPtCr grains. Lattice spacings of CoPtCr grown on Pt with SiO are 0.7% expanded in comparison with CoPtCr grown on Pt without SiO . The EELS studies suggested that Co and Cr atoms are partly oxidized by SiO addition for both samples and Cr atoms are more oxidized for CoPtCr-SiO /Pt samples. © 2005 The Japan Institute of Metals. 2 2 2 2 2 2 2 2 2 2

  236. HRTEM and EELS studies of L1<inf>0</inf>-ordered FePt nano-clusters on MgO films prepared below 673 K 査読有り

    Shunsuke Fukami, Akichika Ohno, Nobuo Tanaka

    Materials Transactions 45 (7) 2012-2017 2004年7月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.45.2012  

    ISSN:1345-9678

    eISSN:1347-5320

    詳細を見る 詳細を閉じる

    Three kinds of FePt-MgO granular films were prepared by a vacuum successive deposition of MgO, Pt, Fe and MgO on a cleaved surface of sodium chloride below 673 K. Their microstructures, electronic structures and magnetic properties were studied by high-resolution transmission electron microscopy (HRTEM), electron energy-loss spectroscopy (EELS) and measurement with a superconducting quantum interference device (SQUID) magnetometer. The TEM observations and selected area electron diffraction patterns revealed that the samples mainly consist of few nm-sized FePt clusters embedded in MgO films with L1 -ordered structure and c-axis perpendicular to the film surface. Size effect on the stability of L1 phase in the FePt nano-clusters was directly observed in [MgO/Fe(0.38nm)/Pt(0.30nm)/MgO] and the critical size of the transition from L1 to Al phase was estimated as around 2 nm, that can be considered as smaller than effective size for the transition from ferromagnetism to superparamagnetism. Coercivity of [MgO/Fe(1.0nm)/Pt(0.8nm)/MgO] was 1.2 × 10 A/m. The Fe-L white-line ratios of the present samples measured by EELS were about 4.0, independently on the incident direction of electron beam. The higher white-line ratio may be attributed to their high-spin state by a change of 3d-band structure owing to the hybridization of d-bands between Fe and Pt atoms. 0 0 0 2,3 5

  237. Microstructure change of vanadium clusters in ZnO crystalline films by heat-treatment 査読有り

    Huayong Pan, Akichika Ohno, Shunsuke Fukami, Jun Yamasaki, Nobuo Tanaka

    Nanotechnology 15 (6) S420-S427 2004年6月

    出版者・発行元:IOP PUBLISHING LTD

    DOI: 10.1088/0957-4484/15/6/020  

    ISSN:0957-4484

    詳細を見る 詳細を閉じる

    Vanadium clusters with a size of several nanometres can be dispersively distributed in ZnO films by using co-deposition. EELS mapping of V-L , HRTEM images, SAD patterns and EELS are a good combination for characterizing nanometre-sized V clusters embedded in a ZnO system. There is no obvious orientation relationship between V and ZnO lattices due to a less good match between ZnO and V atomic planes. The ratio of the vanadium L-white lines of vanadium clusters embedded in ZnO becomes bigger than that of the bulk. The samples were observed in situ from 298 to 923 K with a heating holder so as to study the aggregation process of vanadium clusters in the ZnO crystalline matrix. First, the size of the ZnO crystal grains becomes bigger after the sample is heated at 623 K for an hour; second, the size of ZnO and vanadium particles grows bigger after the sample is heated at 723 K for half an hour, and another orientation relationship between ZnO and vanadium appears; third, after the sample is heated at 873 K for half an hour, the size of vanadium becomes smaller, while V particles and ZnO begin to react and form another phase; finally, Zn VU phase is formed after the sample is heated at 923 K for half an hour. 2,3 2 7

  238. Electron tomography of nano-magnetic materials less than 1 nm resolution 査読有り

    N. Tanaka, A. Ohno, S. Fukami, J. Yamasaki

    Microscopy and Microanalysis 10 (SUPPL. 2) 1176-1177 2004年

    DOI: 10.1017/S1431927604887046  

    ISSN:1431-9276

  239. Theoretical consideration of the stability of an L1<inf>0</inf> magnetic phase in Fe-(Pd, Pt) alloy clusters 査読有り

    S. Fukami, N. Tanaka

    Philosophical Magazine Letters 84 (1) 33-40 2004年1月

    出版者・発行元:TAYLOR & FRANCIS LTD

    DOI: 10.1080/09500830310001628257  

    ISSN:0950-0839

    eISSN:1362-3036

    詳細を見る 詳細を閉じる

    Size effects on the order-disorder transition of binary alloy clusters, particularly Fe-(Pd, Pt) clusters, are studied theoretically, based on the theory of Bragg and Williams. Including the broken bonds at surfaces (interfaces) of the clusters, the relationship between the degree of order and the cluster size, which has recently been suggested from various experimental studies, is formulated. The dependences of the critical size on the temperature and the order-disorder transformation temperature on the cluster size are derived. There is a slight quantitative disagreement with experiment, but this may be improved by considering some modification of higher-order terms.

  240. HRTEM Studies of nm-Size FePd Particles Embedded in MgO after Annealing over 920 K 査読有り

    Huayong Pan, Shunsuke Fukami, Jun Yamasaki, Nobuo Tanaka

    Materials Transactions 44 (10) 2048-2054 2003年10月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.44.2048  

    ISSN:1345-9678

    eISSN:1347-5320

    詳細を見る 詳細を閉じる

    FePd particles were fabricated in MgO crystalline films by using an ultra-high vacuum (UHV) co-deposition method. As-deposited samples and samples annealed at 973 K and 1073 K were studied by high resolution electron microscopy (HRTEM). The as-deposited FePd particles were in a disordered fee phase with a = 0.3837nm and have a certain epitaxial orientations i.e. [100] (001) ∥ [100] (001) . The size of particles was about 2-3 nm and separated distance of particles was about 3-4 nm. After the as-deposited sample was annealed at 973 K for 24 hours, there were neither change in particle size and separated distance, nor phase transformation to take place from disordered fee to L1 order structure. Only change was that lattice fringes in the FePd particles became more straight and regularly spaced than those of the as-deposited sample, and faults within the FePd particles became less than those of the as-deposited sample. After the as-deposited sample was annealed at 1073 K for 4 hours, the size of particles became almost about 3-4 nm and separated distance of particles was about 2-3 nm. Some coalescence took place among the particles. There was, however, no transformation to take place from disordered fee to L1 order structure. The reason why L1 order structure of FePd can not be obtained at such higher annealing temperature than the transformation temperature for the bulk is suggested to be that the system energy of small particle was subjected to strain inside, which is caused by large lattice mismatch between FePd and MgO. Fepd MgO 0 0 0

  241. HRTEM studies of mn-size FePd particles embedded in MgO after annealing over 920K 査読有り

    HY Pan, S Fukami, J Yamasaki, N Tanaka

    MATERIALS TRANSACTIONS 44 (10) 2048-2054 2003年10月

    出版者・発行元:JAPAN INST METALS

    DOI: 10.2320/matertrans.44.2048  

    ISSN:1345-9678

    eISSN:1347-5320

    詳細を見る 詳細を閉じる

    FePd particles were fabricated in MgO crystalline films by using an ultra-high vacuum (UHV) co-deposition method. As-deposited samples and samples annealed at 973 K and 1073 K were studied by high resolution electron microscopy (HRTEM). The as-deposited FePd particles were in a disordered fcc phase with a = 0.3837 nm and have a certain epitaxial orientations i.e. [100] (001)(FePd)parallel to[100] (001)(MgO). The size of particles was about 2-3 nm and separated distance of particles was about 3-4 nm. After the as-deposited sample was annealed at 973 K for 24 hours, there were neither change in particle size and separated distance, nor phase transformation to take place from disordered fcc to L1(0) order structure. Only change was that lattice fringes in the FePd particles became more straight and regularly spaced than those of the as deposited sample, and faults within the FePd particles became less than those of the as-deposited sample. After the as-deposited sample was annealed at 1073 K for 4 hours, the size of particles became almost about 3-4 nm and separated distance of particles was about 2-3 nm. Some coalescence took place among the particles. There was, however, no transformation to take place from disordered fcc to L1(0) order structure. The reason why L1(0) order structure of FePd can not be obtained at such higher annealing temperature than the transformation temperature for the bulk is suggested to be that the system energy of small particle was subjected to strain inside, which is caused by large lattice mismatch between FePd and MgO.

︎全件表示 ︎最初の5件までを表示

MISC 68

  1. 確率ビット向け微細磁性体の熱ゆらぎ 招待有り 査読有り

    金井駿, 深見俊輔, 大野英男

    日本物理学会誌 78 (5) 256-261 2023年5月

    DOI: 10.11316/butsuri.78.5_256  

  2. Coherent antiferromagnetic spintronics

    Jiahao Han, Ran Cheng, Luqiao Liu, Hideo Ohno, Shunsuke Fukami

    Nature Materials 2023年

    DOI: 10.1038/s41563-023-01492-6  

    ISSN:1476-1122

    eISSN:1476-4660

    詳細を見る 詳細を閉じる

    Antiferromagnets have attracted extensive interest as a material platform in spintronics. So far, antiferromagnet-enabled spin–orbitronics, spin-transfer electronics and spin caloritronics have formed the bases of antiferromagnetic spintronics. Spin transport and manipulation based on coherent antiferromagnetic dynamics have recently emerged, pushing the developing field of antiferromagnetic spintronics towards a new stage distinguished by the features of spin coherence. In this Review, we categorize and analyse the critical effects that harness the coherence of antiferromagnets for spintronic applications, including spin pumping from monochromatic antiferromagnetic magnons, spin transmission via phase-correlated antiferromagnetic magnons, electrically induced spin rotation and ultrafast spin–orbit effects in antiferromagnets. We also discuss future opportunities in research and applications stimulated by the principles, materials and phenomena of coherent antiferromagnetic spintronics.

  3. Domain wall memory: Physics, materials, and devices

    Durgesh Kumar, Tianli Jin, Rachid Sbiaa, Mathias Kläui, Subhankar Bedanta, Shunsuke Fukami, Dafine Ravelosona, See Hun Yang, Xiaoxi Liu, S. N. Piramanayagam

    Physics Reports 958 1-35 2022年5月5日

    出版者・発行元:Elsevier BV

    DOI: 10.1016/j.physrep.2022.02.001  

    ISSN:0370-1573

    詳細を見る 詳細を閉じる

    Digital data, generated by corporate and individual users, is growing day by day due to a vast range of digital applications. Magnetic hard disk drives (HDDs) currently fulfill the demand for storage space, required by this data growth. Although flash memory devices are replacing HDDs in applications like mobile phones, laptops, and desktops, HDDs cover the majority of digital data stored in the cloud and servers. Since the capacity growth of HDDs is slowing down, it is essential to look for a potential alternative. One such alternative is domain wall (DW) memory, where magnetic domains in the form of two-dimensional or three-dimensional wires are used to store the information. DW memory (DWM) devices should satisfy the four basic operations, such as writing (nucleating domains or inserting DWs in memory element), storing (stabilizing DWs), shifting (moving DWs), and reading (reading magnetization direction). An external magnetic field or spin-transfer torque can be used to write the information. Spin–orbit torque or electric field may be used for shifting the DWs. The information can be read using tunneling magnetoresistance. The domains may be stored along the tracks using artificial pinning potentials. The absence of moving parts makes the DWM consume less power as compared to HDDs, and be more robust. The potential to stack many layers to store information in three dimensions makes them potentially a large storage capacity device. In addition to memory, DW devices also offer a route for making synaptic devices for neuromorphic computing. Despite these potential advantages of DWM, significant advances in research are needed before DWM could become commercially viable. One of the major challenges associated with DWM is DW dynamics. Many problems, such as controlled DW motion, the stability of domains, reducing the dimensions of the DW devices are still to be addressed. Artificial pinning sites fabricated through either geometrical or non-geometrical methods have been proposed for controlling DW motion. This review paper presents a survey of the investigations carried out so far and the future perspective of such devices.

  4. Neuromorphic spintronics

    J. Grollier, D. Querlioz, K. Y. Camsari, K. Everschor-Sitte, S. Fukami, M. D. Stiles

    Nature Electronics 3 (7) 360-370 2020年7月1日

    DOI: 10.1038/s41928-019-0360-9  

    eISSN:2520-1131

    詳細を見る 詳細を閉じる

    Neuromorphic computing uses brain-inspired principles to design circuits that can perform computational tasks with superior power efficiency to conventional computers. Approaches that use traditional electronic devices to create artificial neurons and synapses are, however, currently limited by the energy and area requirements of these components. Spintronic nanodevices, which exploit both the magnetic and electrical properties of electrons, can increase the energy efficiency and decrease the area of these circuits, and magnetic tunnel junctions are of particular interest as neuromorphic computing elements because they are compatible with standard integrated circuits and can support multiple functionalities. Here, we review the development of spintronic devices for neuromorphic computing. We examine how magnetic tunnel junctions can serve as synapses and neurons, and how magnetic textures, such as domain walls and skyrmions, can function as neurons. We also explore spintronics-based implementations of neuromorphic computing tasks, such as pattern recognition in an associative memory, and discuss the challenges that exist in scaling up these systems.

  5. 不揮発性スピントロニクス素子技術 ー大容量化、高速化、多機能化に向けた取り組みー 招待有り

    深見俊輔, 大野英男

    日本学術振興会 先端ナノデバイス・材料テクノロジー第151委員会 平成30年度 第6回研究会資料 「スピントロニクスの新たな展開と展望」 17-25 2019年2月

  6. 限界に迫る極微細磁気トンネル接合素子 招待有り 査読有り

    深見 俊輔, 大野 英男

    物理科学雑誌『パリティ』 33 (12) 60-63 2018年12月

  7. 反強磁性金属を用いたスピン軌道トルク磁化反転 招待有り

    深見俊輔, 大野英男

    日本磁気学会誌『まぐね』 13 (5) 223-228 2018年11月

  8. アナログスピン軌道トルクを用いた人工ニューラルネットワーク 招待有り

    深見俊輔, William A. Borders, Aleksandr Kurenkov, 張超亮, Samik DuttaGupta, 大野英男

    日本磁気学会研究会資料 216 2018年1月

  9. 招待講演 アナログスピントロニクス素子とその人工神経回路網応用 (磁気記録・情報ストレージ)

    秋間 学尚, BORDERS William, 深見 俊輔, 守谷 哲, 栗原 祥太, KURENKOV Aleksandr, 堀尾 喜彦, 佐藤 茂雄, 大野 英男

    電子情報通信学会技術研究報告 = IEICE technical report : 信学技報 117 (247) 7-12 2017年10月19日

    出版者・発行元:電子情報通信学会

    ISSN:0913-5685

  10. 招待講演 アナログスピントロニクス素子とその人工神経回路網応用 (マルチメディアストレージ)

    秋間 学尚, BORDERS William, 深見 俊輔, 守谷 哲, 栗原 祥太, KURENKOV Aleksandr, 堀尾 喜彦, 佐藤 茂雄, 大野 英男

    映像情報メディア学会技術報告 = ITE technical report 41 (34) 7-12 2017年10月

    出版者・発行元:映像情報メディア学会

    ISSN:1342-6893

  11. スピン軌道トルクによる高速磁化反転とその応用 招待有り

    深見俊輔, 大野英男

    応用物理 86 (7) 565-569 2017年7月

    出版者・発行元:応用物理学会

    ISSN:0369-8009

  12. IoT高性能化の切り札 超高速不揮発メモリ 招待有り

    深見 俊輔

    セラミックス 51 (11) 801-801 2016年11月

  13. 3端子スピン軌道トルク磁気メモリ素子 ~ 高速低消費電力不揮発性集積回路の実現を目指して ~ 招待有り

    深見俊輔, 姉川哲朗, 大河原綾人, 張 超亮, 大野英男

    信学技報 116 (172) 99-103 2016年8月

    出版者・発行元:映像情報メディア学会

    ISSN:1342-6893

  14. スピン軌道トルク磁化反転とその集積回路応用 招待有り

    深見俊輔, 張 超亮, 姉川 哲朗, Samik DuttaGupta, Aleksandr Kurenkov, 大野 英男

    日本磁気学会研究会資料 208 15-22 2016年6月

  15. 招待講演 待機電力重視アプリケーション向け90nm三端子MRAM混載不揮発マイクロコントローラ (集積回路)

    崎村 昇, 辻 幸秀, 根橋 竜介, 本庄 弘明, 森岡 あゆ香, 石原 邦彦, 木下 啓藏, 深見 俊輔, 三浦 貞彦, 笠井 直記, 遠藤 哲郎, 大野 英男, 羽生 貴弘, 杉林 直彦

    電子情報通信学会技術研究報告 = IEICE technical report : 信学技報 114 (175) 39-44 2014年8月4日

    出版者・発行元:一般社団法人電子情報通信学会

    ISSN:0913-5685

    詳細を見る 詳細を閉じる

    本講演では,90nm混載MRAM技術を用いて設計された不揮発性マイクロコントローラの構成について述べる.本チップは,動作速度,動作電圧,信頼性に優れた特長を有する三端子磁気抵抗素子を用いて,メモリとロジックの両方が不揮発化されている.これにより,センサーノードで必要なスタンバイリーク・ゼロと瞬時システム復帰が可能な間欠動作が可能となる.また,MRAMを混載しても超低消費電力マイコン市場の主流である20MHzの動作周波数を達成できた.

  16. 27aPS-19 MgO/Co/Ptにおける磁気異方性の電界変調(27aPS 領域3ポスターセッション,領域3(磁性))

    山田 貴大, 柿堺 悠, 島村 一利, 河口 真志, 深見 俊輔, 石綿 延行, 千葉 大地, 小野 輝男

    日本物理学会講演概要集 69 (0) 479-479 2014年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  17. 27aPS-31 強磁性金属薄膜における電流誘起有効磁場の膜厚依存性(27aPS 領域3ポスターセッション,領域3(磁性))

    河口 真志, 島村 一利, 深見 俊輔, 松倉 文礼, 大野 英男, 森山 貴広, 千葉 大地, 小野 輝男

    日本物理学会講演概要集 69 (0) 481-481 2014年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  18. スピントロニクス論理集積回路の実現に向けた3端子磁壁移動素子の開発 招待有り

    深見俊輔, 大野英男

    工業材料 62 (1) 32-33 2014年1月

    出版者・発行元:日刊工業新聞社

  19. 27aKF-1 垂直磁化Co/Ni細線中の磁壁電流駆動におけるスピンホール効果の影響(スピントロニクス(磁化ダイナミクス),領域3(磁性,磁気共鳴))

    吉村 瑶子, 小山 知弘, 森山 貴広, Kim Kab-Jin, 千葉 大地, 仲谷 栄伸, 深見 俊輔, 山ノ内 路彦, 大野 英男, 小野 輝男

    日本物理学会講演概要集 68 (2) 415-415 2013年8月26日

    出版者・発行元:一般社団法人日本物理学会

    ISSN:1342-8349

  20. 27pXA-4 垂直磁化Co/Ni多層膜における磁壁電流駆動現象の磁性層膜厚依存性(27pXA スピントロニクス(スピン依存伝導),領域3(磁性,磁気共鳴))

    谷川 博信, 鈴木 哲広, 深見 俊輔, 末光 克巳, 大嶋 則和, 苅屋田 英嗣

    日本物理学会講演概要集 68 (1) 539-539 2013年3月26日

    出版者・発行元:一般社団法人日本物理学会

    ISSN:1342-8349

  21. 27pXA-6 Current pulse width dependence of magnetic domain wall motion in the presence of bias magnetic field

    Kim Kab-Jin, Chiba D., Nakatani Y., Fukami S., Yamanouchi M., Ohno H., Ono T.

    日本物理学会講演概要集 68 (1) 540-540 2013年3月26日

    出版者・発行元:一般社団法人日本物理学会

    ISSN:1342-8349

  22. 25aPS-20 透明ゲート電極下のCo/Pt細線における磁壁移動のKerr顕微鏡による観察(II)(領域3ポスターセッション(スピントロニクス・表面・界面磁性・マルチフェロイクス・遍歴磁性・磁性一般),領域3(磁性,磁気共鳴))

    柿堺 悠, 山田 貴大, 河口 真志, 島村 一利, 深見 俊輔, 石綿 延行, 千葉 大地, 小野 輝勇

    日本物理学会講演概要集 68 (0) 366-366 2013年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  23. 26aPS-15 非対称な膜構成を持つ強磁性金属薄膜における異常磁気抵抗効果(26aPS 領域3ポスターセッション,領域3(磁性,磁気共鳴))

    河口 真志, 島村 一利, 深見 俊輔, 松倉 文礼, 大野 英男, 千葉 大地, 小野 輝男

    日本物理学会講演概要集 68 (0) 501-501 2013年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  24. 27aXA-7 透明ゲート電極下のCo/Pt細線における磁壁移動のKerr顕微鏡による観察(27aXA スピントロニクス(ナノ磁性体),領域3(磁性,磁気共鳴))

    柿堺 悠, 河口 真志, 山田 貴大, 島村 一利, 深見 俊輔, 石綿 延行, 千葉 大地, 小野 輝男

    日本物理学会講演概要集 68 (0) 536-536 2013年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  25. 27aXA-10 Co超薄膜における磁気異方性の電界制御(27aXA スピントロニクス(ナノ磁性体),領域3(磁性,磁気共鳴))

    山田 貴大, 柿堺 悠, 島村 一利, 河口 真志, 深見 俊輔, 石綿 延行, 千葉 大地, 小野 輝男

    日本物理学会講演概要集 68 (0) 536-536 2013年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  26. 25aPS-11 Pt/Co/MgO界面垂直磁気異方性の電界による変調(領域3ポスターセッション(スピントロニクス・表面・界面磁性・マルチフェロイクス・遍歴磁性・磁性一般),領域3(磁性,磁気共鳴))

    山田 貴大, 柿堺 悠, 島村 一利, 河口 真志, 深見 俊輔, 石綿 延行, 千葉 大地, 小野 輝男

    日本物理学会講演概要集 68 (0) 364-364 2013年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  27. 27aKF-3 強磁性金属薄膜における電流誘起有効磁場の直流ホール測定による決定(スピントロニクス(磁化ダイナミクス),領域3(磁性,磁気共鳴))

    河口 真志, 島村 一利, 深見 俊輔, 松倉 文礼, 大野 英男, 森山 貴広, 千葉 大地, 小野 輝男

    日本物理学会講演概要集 68 (0) 416-416 2013年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  28. 遷移金属強磁性体における磁性の電界制御

    千葉 大地, 島村 一利, 河口 真志, 小野 新平, 深見 俊輔, 石綿 延行, 小林 研介, 小野 輝男

    日本磁気学会研究会資料 = Bulletin of Topical Symposium of the Magnetics Society of Japan 186 1-3 2012年11月2日

    出版者・発行元:日本磁気学会

    ISSN:1882-2940

  29. 電流誘起磁壁移動デバイス開発

    深見俊輔, 大野英男

    応用電子分科会会誌 18 (5) 2012年11月

  30. 27aAA-9 垂直磁化Co/Ni細線における面内磁場下の磁壁電流駆動(27aAA スピントロニクス(磁気渦・磁壁・磁気抵抗・スピントルク),領域3(磁性,磁気共鳴))

    吉村 瑤子, 小山 知弘, 千葉 大地, 深見 俊輔, 山ノ内 路彦, 大野 英男, 仲谷 栄伸, 小野 輝男

    日本物理学会講演概要集 67 (0) 533-533 2012年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  31. 20aCC-10 垂直磁化Co/Ni細線における面内磁場下の磁壁電流駆動(II)(20aCC スピントロニクス(磁化ダイナミクス),領域3(磁性,磁気共鳴))

    吉村 瑤子, 小山 知弘, 千葉 大地, 深見 俊輔, 山ノ内 路彦, 大野 英男, 仲谷 栄伸, 小野 輝男

    日本物理学会講演概要集 67 (0) 427-427 2012年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  32. 27aAA-8 磁壁電流駆動を用いたCo/Ni細線におけるスピン分極率の温度依存性(27aAA スピントロニクス(磁気渦・磁壁・磁気抵抗・スピントルク),領域3(磁性,磁気共鳴))

    上田 浩平, 仲谷 栄伸, 小野 輝男, 小山 知弘, 平松 亮, 千葉 大地, 深見 俊輔, 谷川 博信, 鈴木 哲広, 大嶋 則和, 石綿 延行

    日本物理学会講演概要集 67 (0) 533-533 2012年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  33. 24aPS-14 Co超薄膜におけるイオン液体を用いた磁性制御(24aPS 領域3ポスターセッション,領域3(磁性,磁気共鳴))

    島村 一利, 千葉 大地, 川口 真志, 小野 新平, 深見 俊輔, 石綿 延行, 小林 研介, 小野 輝男

    日本物理学会講演概要集 67 (0) 478-478 2012年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  34. 24aPS-27 遷移金属強磁性体薄膜における電場効果(24aPS 領域3ポスターセッション,領域3(磁性,磁気共鳴))

    川口 真志, 千葉 大地, 深見 俊輔, 島村 一利, 小野 輝男

    日本物理学会講演概要集 67 (0) 481-481 2012年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  35. 24aPS-28 Co/Ni細線における磁壁内の磁化回転検出の試みII(24aPS 領域3ポスターセッション,領域3(磁性,磁気共鳴))

    平松 亮, 近藤 浩太, 小山 知弘, 千葉 大地, 深見 俊輔, 石綿 延行, 仲谷 栄伸, 小野 輝男

    日本物理学会講演概要集 67 (0) 481-481 2012年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  36. 24aPS-29 電流誘起磁壁速度と磁場誘起磁壁速度の加算性について(24aPS 領域3ポスターセッション,領域3(磁性,磁気共鳴))

    小山 知弘, 上田 浩平, 千葉 大地, 深見 俊輔, 石綿 延行, 河野 浩, 仲谷 栄伸, 小林 研介, 小野 輝男

    日本物理学会講演概要集 67 (0) 481-481 2012年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  37. 19aCC-10 電気二重層を用いた鉄超薄膜における電界効果(19aCC スピントロニクス(熱・力学的スピン・磁化制御),領域3(磁性,磁気共鳴))

    河口 真志, 島村 一利, 小野 新平, 深見 俊輔, 松倉 文礼, 大野 英男, 千葉 大地, 小野 輝男

    日本物理学会講演概要集 67 (0) 413-413 2012年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  38. 19aCC-12 Co/Ni細線における磁壁内の磁化回転検出の試みIII(19aCC スピントロニクス(熱・力学的スピン・磁化制御),領域3(磁性,磁気共鳴))

    平松 亮, 小山 知弘, 千葉 大地, 深見 俊輔, 石綿 延行, 仲谷 栄伸, 小野 輝男

    日本物理学会講演概要集 67 (0) 414-414 2012年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  39. 磁気トンネル接合素子のプラズマプロセス誘起ダメージとリカバリーの試み

    木下啓藏, 山本直志, 本庄弘明, 末光克巳, 石綿延行, 大嶋則和, 深見俊輔, 山本弘輝, 森田正, 笠井直記, 杉林直彦, 池田正二, 大野英男

    応用物理学会学術講演会講演予稿集(CD-ROM) 72nd ROMBUNNO.31P-M-5 2011年8月16日

  40. 26aPS-24 電流印加下におけるデピニング磁場測定(26aPS 領域3ポスターセッション,領域3(磁性,磁気共鳴))

    平松 亮, 近藤 浩太, 千葉 大地, 深見 俊輔, 石綿 延行, 小野 輝男

    日本物理学会講演概要集 66 (0) 489-489 2011年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  41. 26aPS-35 Co/Ni細線における磁壁電流駆動の温度依存性II(26aPS 領域3ポスターセッション,領域3(磁性,磁気共鳴))

    上田 浩平, 小野 輝男, 小山 知弘, 千葉 大地, 谷川 博信, 深見 俊輔, 鈴木 哲広, 大嶋 則和, 石綿 延行, 仲谷 栄伸

    日本物理学会講演概要集 66 (0) 492-492 2011年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  42. 28aHF-8 磁壁回転素子の開発2(28aHF スピントロニクス(スピンホール効果,ナノ磁性),領域3(磁性,磁気共鳴))

    近藤 浩太, 仲谷 栄伸, 平松 亮, 千葉 大地, 深見 俊輔, 石綿 延行, 小野 輝男

    日本物理学会講演概要集 66 (0) 515-515 2011年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  43. 21aPS-31 Co/Ni細線における磁壁内の磁化回転検出の試み(21aPS 領域3ポスターセッション,領域3(磁性,磁気共鳴))

    平松 亮, 近藤 浩太, 小山 知弘, 千葉 大地, 深見 俊輔, 石綿 延行, 仲谷 栄伸, 小野 輝男

    日本物理学会講演概要集 66 (0) 379-379 2011年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  44. 23pRA-4 垂直磁化Co/Ni細線の磁壁電流駆動の温度依存性(23pRA スピントロニクス(スピントルク・電流誘起ダイナミクス・薄膜・微粒子),領域3(磁性,磁気共鳴))

    上田 浩平, 小野 輝男, 小山 知弘, 千葉 大地, 深見 俊輔, 谷川 博信, 鈴木 哲広, 大嶋 則和, 石綿 延行, 仲谷 栄伸

    日本物理学会講演概要集 66 (0) 450-450 2011年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  45. 23pRA-5 磁壁電流駆動における閾電流密度に対する外部磁場の影響II(23pRA スピントロニクス(スピントルク・電流誘起ダイナミクス・薄膜・微粒子),領域3(磁性,磁気共鳴))

    小山 知弘, 小野 輝男, 上田 浩平, 千葉 大地, 深見 俊輔, 谷川 博信, 鈴木 哲広, 大嶋 則和, 石綿 延行, 仲谷 栄伸

    日本物理学会講演概要集 66 (0) 450-450 2011年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  46. 28aHF-9 SPELEEMを用いたCo/Ni細線中の電流誘起磁壁移動観察(28aHF スピントロニクス(スピンホール効果,ナノ磁性),領域3(磁性,磁気共鳴))

    小山 知弘, 石綿 延行, 木下 豊彦, 小野 輝男, 大嶋 則和, 千葉 大地, 小嗣 真人, 大河内 拓雄, 谷川 博信, 深見 俊輔, 永原 聖万, 鈴木 哲広

    日本物理学会講演概要集 66 (0) 516-516 2011年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  47. スピン移行トルク磁壁移動を用いた高速磁気ランダムアクセスメモリ

    三浦貞彦, 深見俊輔, 鈴木哲広, 永原聖万, 大嶋則和, 加藤有光, 斉藤信作, 根橋竜介, 崎村昇, 本庄弘明, 森馨, 谷川博信, 石綿延行, 杉林直彦

    半導体・集積回路技術シンポジウム講演論文集 74th 89-92 2010年7月8日

    出版者・発行元:電気化学会電子材料委員会

  48. 電流誘起磁壁移動現象の高速MRAMへの応用 招待有り

    石綿延行, 深見俊輔, 鈴木哲弘, 大嶋則和, 永原聖万, 三浦貞彦, 杉林直彦

    日本磁気学会誌 5 (4) 178-183 2010年4月

    出版者・発行元:日本磁気学会

    ISSN:1880-7208

  49. 20pGJ-2 外部磁場によるCo/Ni細線中の磁壁伝搬観測(20pGJ 磁壁,磁化ダイナミクス,領域3(磁性,磁気共鳴))

    山田 啓介, 小林 研介, 小野 輝男, Jamet J. P, Ferre J, Thiaville A, 深見 俊輔, 鈴木 哲広, 大嶋 則和, 石綿 延行, 千葉 大地

    日本物理学会講演概要集 65 (0) 466-466 2010年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  50. 20aPS-28 細線形状制御による磁壁駆動電流密度の低減(20aPS 領域3ポスターセッション(薄膜・人工格子・表面・微小領域・スピントロニクス・遍歴・化合物磁性),領域3(磁性,磁気共鳴))

    小山 知弘, 仲谷 栄伸, 小野 輝男, 上田 浩平, 山田 元, 千葉 大地, 谷川 博信, 深見 俊輔, 鈴木 哲広, 大嶋 則和, 石綿 延行

    日本物理学会講演概要集 65 (0) 455-455 2010年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  51. 20pGJ-3 Co/Ni多層膜細線における磁壁電流駆動の積層膜厚および膜厚比率依存性(20pGJ 磁壁,磁化ダイナミクス,領域3(磁性,磁気共鳴))

    上田 浩平, 仲谷 栄伸, 小野 輝男, 小山 知弘, 山田 元, 千葉 大地, 谷川 博信, 深見 俊輔, 鈴木 哲広, 大嶋 則和, 石綿 延行

    日本物理学会講演概要集 65 (0) 466-466 2010年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  52. 20pGJ-4 垂直磁気異方性を有するCo/Ni細線における複数磁壁電流駆動II(20pGJ 磁壁,磁化ダイナミクス,領域3(磁性,磁気共鳴))

    山田 元, 仲谷 栄伸, 小野 輝男, 小山 知弘, 上田 浩平, 千葉 大地, 谷川 博信, 深見 俊輔, 鈴木 哲広, 大嶋 則和, 石綿 延行

    日本物理学会講演概要集 65 (0) 466-466 2010年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  53. 24aWP-5 磁壁電流駆動における閾電流密度に対する外部磁場の影響(24aWP 磁化ダイナミクス,領域3(磁性,磁気共鳴))

    小山 知弘, 小野 輝男, 上田 浩平, 千葉 大地, 谷川 博信, 深見 俊輔, 鈴木 哲広, 大嶋 則和, 石綿 延行, 仲谷 栄伸

    日本物理学会講演概要集 65 (0) 377-377 2010年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  54. 25aPS-34 磁壁オシレーターの開発(25aPS 領域3ポスターセッション,領域3(磁性,磁気共鳴))

    近藤 浩太, 仲谷 栄伸, 千葉 大地, 深見 俊輔, 石綿 延行, 小野 輝男

    日本物理学会講演概要集 65 (0) 406-406 2010年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  55. 25aPS-43 Co/Ni細線における磁壁電流駆動の温度依存性(25aPS 領域3ポスターセッション,領域3(磁性,磁気共鳴))

    上田 浩平, 小野 輝男, 小山 知弘, 千葉 大地, 谷川 博信, 深見 俊輔, 鈴木 哲広, 大嶋 則和, 石綿 延行, 仲谷 栄伸

    日本物理学会講演概要集 65 (0) 408-408 2010年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  56. SoC混載に適した垂直磁化磁壁移動型MRAM

    石綿延行, 深見俊輔, 鈴木哲広, 永原聖万, 大嶋則和, 尾崎康亮, 齊藤信作, 根橋竜介, 崎村昇, 本庄弘明, 森馨, 五十嵐忠二, 三浦貞彦, 杉林直彦

    日本磁気学会研究会資料 168th 41-45 2009年11月2日

    出版者・発行元:日本磁気学会

    ISSN:1882-2940

  57. 垂直磁化磁壁移動セルを用いた高速低電流MRAM 招待有り

    深見俊輔, 鈴木哲広, 永原聖万, 大嶋則和, 斉藤信作, 尾崎康亮, 根橋竜介, 崎村昇, 本庄弘明, 森馨, 五十嵐忠二, 三浦貞彦, 石綿延行, 杉林直彦

    信学技報、IEICE Technical Report SDM2009-114, ICD2009-30 2009年7月

    ISSN:0913-5685

  58. MRAMの技術動向,今後の展開,32MbMRAM開発

    杉林直彦, 根橋竜介, 崎村昇, 本庄弘明, 斉藤信作, 伊藤雄一, 三浦貞彦, 加藤有光, 森馨, 尾崎康亮, 小林洋介, 大嶋則和, 木下啓藏, 鈴木哲広, 永原聖万, 石綿延行, 末光克巳, 深見俊輔, 波田博光, 笠井直記

    電子情報通信学会技術研究報告 109 (2(ICD2009 1-12)) 13-17 2009年4月6日

    出版者・発行元:一般社団法人電子情報通信学会

    ISSN:0913-5685

    詳細を見る 詳細を閉じる

    MRAMは、磁性体を使用した書き換え回数制限のない唯一の不揮発メモリである。MRAMの最近の技術動向とその特徴を活かした応用先について議論し、今後の展開についての見通しについて述べる。我々は、MRAMの特徴は混載メモリに向いていると考え、2T1MTJ方式のメモリセルを中心に開発してきた。その最新の結果である32MbMRAMの試作について述べる。

  59. 27pTF-2 垂直磁気異方性を有するCo/Ni細線中の磁壁電流駆動 : 磁壁移動速度の測定(27pTF 細線・トルク,領域3(磁性,磁気共鳴))

    小山 知弘, 小野 輝男, 谷川 博信, 山田 元, 大嶋 則和, 深見 俊輔, 石綿 延行, 千葉 大地, 葛西 伸哉, 仲谷 栄伸

    日本物理学会講演概要集 64 (0) 451-451 2009年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  60. 28aPS-108 垂直磁気異方性を有するCo/Ni細線中の磁壁電流駆動現象 : しきい電流密度の低減(28aPS 領域3ポスターセッション(スピントロニクス・フラストレーション系・実験技術),領域3(磁性,磁気共鳴))

    谷川 博信, 小野 輝男, 小山 知弘, 山田 元, 千葉 大地, 葛西 伸哉, 大嶋 則和, 深見 俊輔, 石綿 延行, 仲谷 栄伸

    日本物理学会講演概要集 64 (0) 482-482 2009年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  61. 28aPS-112 垂直磁気異方性を有するCo/Ni細線への単一磁壁導入(28aPS 領域3ポスターセッション(スピントロニクス・フラストレーション系・実験技術),領域3(磁性,磁気共鳴))

    山田 元, 小野 輝男, 小山 知弘, 谷川 博信, 大嶋 則和, 深見 俊輔, 石綿 延行, 千葉 大地, 葛西 伸哉, 仲谷 栄伸

    日本物理学会講演概要集 64 (0) 483-483 2009年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  62. 25pPSA-27 垂直磁気異方性を有するCo/Ni細線の磁気異方性定数の決定(領域3ポスターセッション(スピントロニクス・遍歴磁性等),領域3,磁性,磁気共鳴)

    上田 浩平, 仲谷 栄伸, 小野 輝男, 小山 知弘, 山田 元, 千葉 大地, 谷川 博信, 深見 俊輔, 鈴木 哲広, 大嶋 則和, 石綿 延行

    日本物理学会講演概要集 64 (0) 344-344 2009年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  63. 25pPSA-29 垂直磁気異方性を有するCo/Ni細線における複数磁壁電流駆動(領域3ポスターセッション(スピントロニクス・遍歴磁性等),領域3,磁性,磁気共鳴)

    山田 元, 仲谷 栄伸, 小野 輝男, 小山 知弘, 上田 浩平, 谷川 博信, 深見 俊輔, 鈴木 哲広, 大嶋 則和, 石綿 延行, 千葉 大地

    日本物理学会講演概要集 64 (0) 344-344 2009年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  64. 27aRA-5 外部磁場下におけるCo/Ni細線中の磁壁電流駆動(磁化ダイナミクス,領域3,磁性,磁気共鳴)

    小山 知弘, 仲谷 栄伸, 小野 輝男, 山田 元, 上田 浩平, 谷川 博信, 深見 俊輔, 鈴木 哲広, 大嶋 則和, 石綿 延行, 千葉 大地

    日本物理学会講演概要集 64 (0) 369-369 2009年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  65. 21pQG-8 垂直磁気異方性を有する強磁性細線中の磁壁電流駆動(21pQG スピントロニクス・微小領域磁性,領域3(磁性,磁気共鳴))

    小山 知弘, 谷川 博信, 近藤 浩太, 大嶋 則和, 深見 俊輔, 石綿 延行, 葛西 伸哉, 小野 輝男

    日本物理学会講演概要集 63 (0) 380-380 2008年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  66. 23aPS-20 垂直磁気異方性を有する強磁性細線中の磁壁電流駆動における細線幅依存性(23aPS ポスターセッション,領域3(磁性,磁気共鳴))

    小山 知弘, 谷川 博信, 近藤 浩太, 大嶋 則和, 深見 俊輔, 石綿 延行, 葛西 伸哉, 小野 輝男

    日本物理学会講演概要集 63 (0) 429-429 2008年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  67. 24aWL-10 垂直磁気異方性を有するCoCrPt細線中の磁壁電流駆動(24aWL 微小領域磁性,領域3(磁性,磁気共鳴))

    谷川 博信, 近藤 浩太, 小山 知弘, 大嶋 則和, 深見 俊輔, 石綿 延行, 葛西 伸哉, 小野 輝男

    日本物理学会講演概要集 63 (0) 475-475 2008年

    出版者・発行元:一般社団法人 日本物理学会

    ISSN:1342-8349

  68. 4Mb MRAMとその応用

    杉林 直彦, 本田 雄士, 崎村 昇, 永原 聖万, 三浦 貞彦, 志村 健一, 辻 清孝, 福本 能之, 本庄 弘明, 鈴木 哲広, 加藤 有光, 齋藤 信作, 笠井 直記, 沼田 秀昭, 大嶋 則和, 根橋 竜介, 末光 克巳, 向井 智徳, 森 馨, 深見 俊輔, 石綿 延行, 波田 博光, 田原 修一

    電子情報通信学会技術研究報告. ICD, 集積回路 106 (2) 61-65 2006年4月6日

    出版者・発行元:一般社団法人電子情報通信学会

    ISSN:0913-5685

    詳細を見る 詳細を閉じる

    新規に開発した4MbMRAMのセル技術、回路技術、試作結果及び応用提案について報告する。メモリセルはトグルセルであり、0.24μmMRAM+0.18μmCMOSルールで設計し、面積は2.24μm^2である。センスアンプ・書込み電流源回路はバーストモード動作ができ、FUSE付レジスタで回路特性を調整しやすいような構成になっている。チップサイズは、5mm×7.8mmである。MRAMの特徴が活きるドライブレコーダへの応用を提案するデモシステムを製作した。

︎全件表示 ︎最初の5件までを表示

共同研究・競争的資金等の研究課題 11

  1. ブレインモルフィックコンピューティングハードウェア基盤の構築

    堀尾 喜彦, 池口 徹, 加藤 秀行, 香取 勇一, KURENKOV ALEKSANDR, 佐藤 茂雄, 島田 裕, 鈴木 秀幸, 深見 俊輔, 藤原 寛太郎

    提供機関:Japan Society for the Promotion of Science

    制度名:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)

    研究種目:Grant-in-Aid for Scientific Research (A)

    研究機関:Tohoku University

    2020年4月1日 ~ 2025年3月31日

    詳細を見る 詳細を閉じる

    1.脳型デバイス・回路基盤の構築:スピントロニクス人工ニューロン・シナプスの材料・素子研究を行うとともに、その数理モデルを検討した。材料・素子研究については、3端子MTJ素子の基礎検討を行い、低消費電力化の知見を得た。数理モデルについては、リーク付き積分特性やスパイクタイミング依存可塑性の実験結果を概ね再現した。また、ニューロン素子に発火機構を付加するため、自励発振機能を有する共鳴トンネルダイオード(RTD)の製作プロセスの確立に向けてプラズマCVD等の条件出しを行った。さらに、CMOS回路との融合のため、基本となるニューロンCMOS回路の設計・試作・評価を行った。 2.脳型基本アーキテクチャの構築:非線形力学的解析手法により、ニューロンモデルの非周期的な応答の解析を可能とした。また、点過程を含む時系列解析手法としてアトラクタ再構成法を検討した。さらに、昨年度構築したスパイキング神経回路網モデルを解析し、神経雪崩現象を確認した。加えて、振動子系の同期・非同期現象や神経伝達物質が脳波リズムに与える影響について調査し、脳神経系の発達と学習の数理モデルを構築した。リザバーニューラルネットワーク(RNN)については、時間遅れRNNから導かれるフィッシャー情報行列の最大固有値に対応する固有ベクトルに基づく入力マスクにより、ノイズ耐性が向上することを示した。一方、応用に関しては、RNN強化学習によるロボット制御のためのモデルを構築した。また、短期シナプス可塑性によりRNNのダイナミクスを拡張し、行動計画タスクの性能を改善した。 3.脳型基本システム試作:1.のデバイスを応用し、2.で提案するアーキテクチャを集積回路として実装するための基本的な準備として、1.で述べたスピントロニクス素子とRTD素子およびCMOS回路を融合させるための基本的な枠組みについて検討した。

  2. 強磁性ワイル半金属のトポロジカルおよび量子効果の開拓とスピントロニクス素子応用

    深見 俊輔

    提供機関:Japan Society for the Promotion of Science

    制度名:Grants-in-Aid for Scientific Research

    研究種目:Grant-in-Aid for JSPS Fellows

    研究機関:Tohoku University

    2023年3月8日 ~ 2024年3月31日

  3. 強磁性ワイル半金属のトポロジカルおよび量子効果の開拓とスピントロニクス素子応用

    深見 俊輔, HAN JIAHAO

    提供機関:Japan Society for the Promotion of Science

    制度名:Grants-in-Aid for Scientific Research Grant-in-Aid for JSPS Fellows

    研究種目:Grant-in-Aid for JSPS Fellows

    研究機関:Tohoku University

    2022年7月27日 ~ 2024年3月31日

  4. 強磁性ワイル半金属のトポロジカルおよび量子効果の開拓とスピントロニクス素子応用

    深見 俊輔, HAN JIAHAO

    2022年4月22日 ~ 2024年3月31日

  5. ノンコリニアスピントロニクス

    深見 俊輔, 家田 淳一, DUTTAGUPTA SAMIK, 金井 駿, 張 超亮

    提供機関:Japan Society for the Promotion of Science

    制度名:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (S)

    研究種目:Grant-in-Aid for Scientific Research (S)

    研究機関:Tohoku University

    2019年6月26日 ~ 2024年3月31日

  6. ストレッチャブルスピンデバイス実現を目指した超瞬間熱処理プロセス構築への挑戦

    千葉 大地, 深見 俊輔

    2021年7月9日 ~ 2023年3月31日

    詳細を見る 詳細を閉じる

    今年度研究開始当初に、この研究の要となるフラッシュランプアニール装置が故障した。海外のメーカー製であり、コロナ禍のため技術者が来日できず、対応に苦慮した。来年度(2022年度)初めに再起動の目途が立ったが、今年度は既存試料の詳細な解析に注力することとした。そこで今年度は、磁気トンネル接合(MTJ)の、熱処理前後の既存試料の微細組織構造や元素分布、アニール過程の観察を、大阪大学超高圧電子顕微鏡センター(阪大電顕センター)にて行うための技術習得と、データどりを急ぐこととした。また、観測用磁気トンネル接合の試料作製や、通常の熱処理炉での条件出しなどを行った。 阪大電顕センターにて、元素分布、つまり特定の元素の拡散の様子の違いを確認できる準備を整えた。具体的には、試料準備の方法、装置の使用方法などを習得する作業を行った。その後、通常の熱処理炉で450℃でアニールを行った試料と、フラッシュランプアニール装置を用いていくつかのコンディションで瞬間アニールした既存試料の、双方の透過型電子顕微鏡像、エネルギー分散型蛍光X線分析(EDX)ラインプロファイルを観察し、結晶化の様子や、元素部分布の違いを観察した。CoFeB/MgO系MTJのBの拡散の様子、下地層やキャップ層元素の拡散の様子などを観察したところ、通常の熱処理炉でアニールした試料では、B(ボロン)が下地層に多く含まれていることなど、特徴的な様子を観測することができた。今年度終盤にはフラッシュランプアニール装置でアニールした試料の観測も行うことができたが、EDXの計測については来年度以降に持ち越しとなった。

  7. スピントロニクスを用いた人工知能ハードウェアパラダイムの創成

    大野 英男, 遠藤 哲郎, 鈴木 大輔, 佐藤 茂雄, 堀尾 喜彦, 深見 俊輔

    提供機関:Japan Society for the Promotion of Science

    制度名:Grants-in-Aid for Scientific Research Grant-in-Aid for Specially Promoted Research

    研究種目:Grant-in-Aid for Specially Promoted Research

    研究機関:Tohoku University

    2017年4月25日 ~ 2022年3月31日

    詳細を見る 詳細を閉じる

    本研究課題は、人工知能(AI)ハードウェアパラダイムの創成を念頭に、不揮発性スピン素子を用いたAIハードウェアとしての集積回路を設計実現することを目指して進めてきた。当初の計画に従い、3つの主要課題、①AIコンピューティングハードウェア向けスピントロニクス素子の開拓、②ノイマン型AIコンピューティングハードウェアの実現、③非ノイマン型AIコンピューティングハードウェアの実現、に対して研究を進めた。 ①については、アナログスピントロニクス素子のダイナミクスを利用することでスパイクタイミング依存可塑性やリーキー・インテグレート・アンド・ファイアなどの非ノイマン型ニューラルネットワークで必要とされるニューロン、シナプスの特性をスピン素子で再現できることなどが分かった。その他、反強磁性/強磁性ヘテロ構造におけるジャロシンスキー・守谷相互作用やスピン軌道トルクなどを評価し、人工知能ハードウェア応用に向けた有用な知見を得た。②については、基本回路の検討、ならびにハードウェアアルゴリズム検討のためのプラットフォーム構築に取り組み、スピン素子ベース多機能・再構成可能演算回路の設計や学習アルゴリズム評価のためのプラットフォーム構築などを進めノイマン型AIハードウェア実現の土台を形成した。③については、非ノイマン型・脳型コンピューティングアーキテクチャの検討、アナログスピンシナプス特性を考慮した学習則、アナログスピンメモリ素子を組み込んだアナログニューラルネットワーク集積回路の構築に向けた詳細な検討を行った。

  8. ノンコリニアスピントロニクス

    深見 俊輔, 家田 淳一, DUTTAGUPTA SAMIK, 金井 駿, 張 超亮

    提供機関:Japan Society for the Promotion of Science

    制度名:Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)

    研究種目:Grant-in-Aid for Scientific Research (A)

    研究機関:Tohoku University

    2019年4月1日 ~ 2020年3月31日

    詳細を見る 詳細を閉じる

    3か月弱の研究期間内においては、ノンコリニア反強磁性材料薄膜の成長技術に関する検討を開始し、方位制御された単結晶試料の作製の見通しを得ることができた。加えて、ノンコリニア磁気構造の代表例である磁気スキルミオンの電流による駆動に成功し、その詳細評価を行った。

  9. 反強磁性ヘテロ構造におけるスピン軌道トルク磁化反転の空間・元素・時間分解観察

    深見 俊輔, KURENKOV ALEKSANDR, DUTTAGUPTA SAMIK, LLANDRO Justin

    2018年10月9日 ~ 2020年3月31日

    詳細を見る 詳細を閉じる

    本研究課題は2018年10月に採択されて研究を開始し、当初は2021年3月に完了予定であったが、研究代表者が申請していた別の研究課題が2019年6月に基盤研究(S)で採択されたことを受け、廃止することとなった。 約9か月の研究期間内において、2018年11月には英国に渡航し、放射光施設Diamond Light Sourceにおいて、共同研究相手であるスイス連邦工科大学のPietro Gambardella教授のグループと共同でX線磁気円二色性および磁気線二色性を用いた顕微鏡観察の実験を行った。研究代表者の深見および分担者のKurenkov、同じく分担者のDuttaGuptaの作製した磁性ヘテロ積層膜からなる微細素子の反強磁性層のネールベクトルおよび強磁性層の磁化の電流に対する応答を観察し、これまでに電気的な測定で得られていた結果の理解につながる有用な知見が得られた。その後、得られた結果を画像処理などから解析するとともにマイクロマグネティックシミュレーションなどを行い、反強磁性/強磁性ヘテロ構造、及び反強磁性/非磁性ヘテロ構造においてスピン軌道トルクによって誘起されるドメインのダイナミクスに関する統一的な理解が得られた。

  10. 極微細世代における新規磁壁移動方式の研究と3次元デバイスへの展開

    深見 俊輔

    提供機関:Japan Society for the Promotion of Science

    制度名:Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (A)

    研究種目:Grant-in-Aid for Young Scientists (A)

    研究機関:Tohoku University

    2015年4月1日 ~ 2018年3月31日

    詳細を見る 詳細を閉じる

    本研究では、極微細細線における電流誘起磁壁移動の新方式を提案、実証し、そこで得られた知見をもとに3次元磁壁移動デバイスの実現指針を検討することを目指して行った。はじめに垂直型の微細化限界を明らかにするとともに垂直型の延命方法を明らかにし、次いでそれとは異なる思想から面内型の新しい可能性を計算で明らかにした上で垂直型では実現できない微細領域での磁壁移動を実証した。最後に3次元磁壁移動デバイス実現のための端緒を得るところまで成功し、当初の研究課題の目標を概ね達成することができた。

  11. スピン軌道トルクを用いた新規磁化制御方式の研究と3端子磁気メモリ素子への応用

    深見 俊輔

    提供機関:Japan Society for the Promotion of Science

    制度名:Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research

    研究種目:Grant-in-Aid for Challenging Exploratory Research

    研究機関:Tohoku University

    2015年4月1日 ~ 2017年3月31日

    詳細を見る 詳細を閉じる

    高性能低消費電力集積回路への応用が期待される新規磁化反転方式を提案し、その動作実証、及び物理的機構の解明、ならびに集積回路応用に向けた基盤技術の構築に取り組んだ。ここ数年盛んな研究が行われている、スピン・軌道相互作用を用いた磁化制御技術―スピン軌道トルク磁化反転―の新方式を考案し、閾電流密度を決める物理的因子やナノ秒ダイナミクスを明らかにした。またサブナノ秒での磁化反転や無磁場動作を実現した。これらによってスピン軌道トルク磁化反転技術の集積回路応用への学理・技術基盤が構築された。

︎全件表示 ︎最初の5件までを表示

その他 2

  1. 極微細世代における新規磁壁移動方式の研究と3次元デバイスへの展開

    詳細を見る 詳細を閉じる

    本研究では極微細世代(30nm以下)での電流誘起磁壁移動を実現する新方式を提案し、微細ナノ磁性体の新たな物理を開拓する。またそこで確立した知見をもとに3次元磁壁移動デバイスの世界初の動作実証へと発展させる。

  2. スピン軌道トルクを用いた新規磁化制御方式の研究と3端子磁気メモリ素子への応用

    詳細を見る 詳細を閉じる

    本研究では、スピン軌道相互作用に由来するトルク―スピン軌道トルク―を用いた新しい磁化制御方式の基礎物理を確立し、それを用いた3端子磁気メモリ素子の実用化のための基盤技術を構築する。