The effect of P addition on the nano-crystallization of Fe81.5Si0.5B15.5-xPxCu0.5C2 (x = 0, 4.5, 7.5, 11 at.%) amorphous alloys under various heating rates has been studied. Appropriate P addition enhanced the thermal stability of Fe–Si–B–P–Cu–C amorphous alloys. The results also revealed that P addition could decrease the required critical heating rate for the low coercivity and improve the magnetic softness of annealed samples. Although as commonly found in most Fe-based nano-crystalline alloys, a small amount of P addition (4.5 at.%) could effectively help reduce the coercivity when a high heating rate was applied during nano-crystallization, the high heating rate failed to decrease the coercivity in 7.5 at.% P-added alloys and even reversely caused the deterioration of magnetic softness for excessive P addition (11 at.%). The unusual phenomenon in the alloy with 11 at.% P addition lies in the fast increase of diffusion rate with rising temperature and delayed nucleation, which are caused by the weakened bond energy and increased segregation energy, respectively. The results suggest that the improvement of magnetic softness for Fe-based nano-crystalline alloys through simply increasing the P addition would meet its ceiling, due to the limited decrease in coercivity and even increase through applying high heating rate with excessive P concentration. The understanding of P role on the nano-crystallization mechanism could contribute to the compositional design of high-performance soft magnetic Fe-based alloys with an acceptable heating rate in industry.

We present the first report on the structural, magnetic, and transport properties of epitaxial thin films of equiatomic quaternary CoFeCrGa, grown on a single crystal MgO(001) substrate. From the structure and surface morphology analyses, we have shown that the films grown are ordered, epitaxial, and homogeneous. Magnetic measurements confirm the soft ferromagnetic nature of the film along the in-plane direction with a coercivity of 4.6 Oe. The resistivity measurements indicate semiconducting nature with a very low temperature coefficient of resistivity (TCR) value, suggesting an almost temperature independent resistivity, similar to other reported spin-gapless semiconductors (SGSs) among the Heusler alloys. A non-saturating, quantum linear magnetoresistance is observed even in high fields of up to 12 kOe, another prerequisite for gapless materials. Hall measurements are also performed, and a detailed analysis has been carried out to estimate the ordinary and anomalous Hall contributions. The conductivity value (σ x x) at 300 K is found to be 4280 S cm - 1, which is comparable with the other reported SGS materials. We have also studied the effect of L2 1 and B2 type disorder on the electronic properties based on the first principle calculations and found that the SGS nature in CoFeCrGa is quite robust against the Co-Fe swap disorder (L2 1 disorder); however, with swap disorder (≥ 25%) between Cr and Ga sites, the system transits from SGS to half-metallic state. All these results indicate the possibility of spin-gapless semiconducting nature in the CoFeCrGa film, making it highly suitable for spin-based device applications.

Coating soft magnetic powders by an insulation layer is an effective way to improve the high-frequency performance of soft magnetic powder cores. The quality of insulation coating is highly dependent of the coating materials and the coating method. In the present work, a commercial amorphous powder (Fe73Si11B11C3Cr2) was primarily coated by a PDA/PEI layer by a co-deposition method in alkaline solution. A thick PDA/PEI layer with good homogeneity was co-deposited on the surface of amorphous soft magnetic powders. The high frequency core loss of magnetic powder cores was reduced by up to ~ 44 % at the magnetic induction of 0.1 T and the frequency of 100 kHz by primarily coating the amorphous powders by PDA/PEI. Microscopic images showed that the PDA/PEI coating layer on the amorphous powders does not peel off while being compressed. These results indicates that PDA/PEI insulation coating is a coating method which can effectively improve the comprehensive magnetic properties of magnetic powder cores.

As a promising candidate of rare-earth free hard magnetic materials, L10-FeNi has been paid much attention in the last decades. However, it is difficult to be artificially fabricated due to its low thermal stability and sluggish diffusion ability of atoms below the crucial temperature of 320 °C. In this study, a promising method of annealing amorphous precursor was extensively developed through (Fe50Ni50)84−xSixP16 (x = 0, 4 at%) and (Fe50Ni50)86−xSixP14 (x = 2, 4, 8 at%) alloys. Especially, the effect of Si on the formation of L10 phase in annealed FeNi-based alloys was investigated and clarified. It is found Fe42Ni42P16 with a much low crystallization temperature could be an appropriate basic amorphous alloy for the formation of L10 phase. The addition of Si enhanced the thermal stability of Fe-Ni-P amorphous alloys. Interestingly, Si could stabilize the L10 phase in annealed samples and increase its disordering temperature above which L10-FeNi phase could deteriorate into soft magnetic phase. As expected, appropriate Si addition indeed improved the hard magnetic properties of the annealed alloys and samples with high coercivity above 900 Oe was obtained. Further Si addition would deteriorate the magnetic-crystalline anisotropy of L10 phase and decrease the coercivity of annealed Fe-Ni-Si-P alloys. Nevertheless, the results indicate that increasing the order-disorder transition temperature through element doping in L10 lattice would be a promising strategy for the massive formation of L10-FeNi like other ordered phases (i.e. L12-FeNi, L10-CoPt), and could substantively contribute to the artificial fabrication of FeNi-based rare-earth free magnets in future.

Creation of FeNi-based hard magnetic materials for a high-density recording media depends on many factors including chemistry, synthesis conditions and subsequent heat-treatments. In particular Fe-Ni thin films can be fabricated by sputtering, molecular beam epitaxy and electrodeposition. The highest values of anisotropy constant are obtained for ordered tP4/L10-FeNi compound. From the viewpoint of practical use, a challenging task is to propose the relevant technological schemes for fabrication of this compound. This work is devoted to a study of three types of materials produced by radio frequency magnetron sputtering: layered Fe/(Ni,Pt) crystalline samples deposited at room temperature and subsequently annealed, homogeneous crystalline Fe(Ni,Pt) samples deposited at elevated substrate temperature and amorphous Fe-Ni-Pt-Zr samples deposited at room temperature which were further crystallized on heating. The phase composition of the sample was studied by X-ray diffractometry while the obtained nanostructure was observed by transmission electron microscopy. Thermally crystallized Fe-Ni-Pt-Zr samples exhibited the best combination of magnetic properties among the deposited films though partial oxidation of the samples took place on sputtering and annealing. Chemical composition and microstructure features, namely grain structure and defects in the Fe(Ni,Pt) samples are proposed to be main reasons responsible for the observed magnetic properties.

<jats:title>Abstract</jats:title><jats:p>Half-metallic fully compensated ferrimagnets (HM-FCFMs) constitute a special class of half-metals exhibiting zero magnetization at zero temperature. While there have been a number of theoretical studies predicting the existence of such materials over the last 25 years, very few of those have been synthesized and observed that they exhibit expected properties. Herein, we demonstrate that a NiAs-type hexagonal-structured (CrFe)S compound could serve as an HM-FCFM material. It has a half-metallic nature of 100% spin-polarised Fermi surfaces and yet zero magnetisation at the ground state. The magnetisation shows linear behaviour as a function of the magnetic field at temperatures below the compensation temperature (~ 190 K). In addition, it shows a high magnetic coercivity of 3.8 T at 300 K. These magnetic features contribute to a significant development in the application of HM-FCFMs for spintronics devices.</jats:p>

We present the results of a comprehensive investigation of electric and thermal transport properties of polycrystalline Bi-substituted La0.95-xBixSr0.05CoO3 for LBSCO-0, 1, and 2. The electrical resistivity reflects the semiconducting nature with n-type to p-type transition ∼52 K for LBSCO-1 and LBSCO-2 samples. In the low temperature region, the dominant transport mechanism is found to be variable range hopping with the hopping range decreasing with increasing temperature from 95 to 20 Å. The substitution of higher atomic weight element Bi at the La site drastically affects the overall thermal conductivity by reducing the lattice contribution (∼0.12 W/m-K at 50 K) and also enhancing the Seebeck coefficient (S ∼354 μV/K). The increase in the resistivity and Seebeck coefficient for the Bi-substituted system is related to the decrease in the available charge carrier concentration (∼5.12 × 1020 cm-3). The overall variation in the Seebeck coefficient depicts a complex nature with a large decreasing trend below 50 K followed by an in-depth analysis of the Debye temperature (∼470 K) and e-ph coupling. These findings suggest that the Bi-substituted LBSCO system has phonon-mediated charge transport via the phonon drag effect below 50 K. Notably, we found a large increment in ZT ∼0.17 at room temperature for LBSCO-2 compositions that is one-order larger than pristine undoped LBSCO-0 and even higher than the other existing cobaltite-based thermoelectric choice.

Ferromagnetic L21 phase of Ni2MnAl with high order degree is difficult to synthesize because of low L21/B2 order-disorder transformation temperature. It is found that magnetic field accelerated the transformation from the antiferromagnetic disordered B2 to ordered L21 phase. Magnetization increased by in-magnetic-field annealing at 673 K, which indicated the acceleration of the ordering to L21 phase. Magnetic field effects on the B2/L21 order-disorder transformation were discussed based on magnetic-field-induced change of transformation temperature, enhancement of degree of order at annealing temperature, and reduction of critical radius of L21 nuclei. Growth kinetics of L21 phase were evaluated by Johnson-Mehl-Avrami equation, which indicated that 15-T annealing accelerated the growth of L21 phase 5.7 times faster than zero-field annealing. Our results showed that magnetic field can contribute to shortening the annealing time for synthesis of ferromagnetic L21-Ni2MnAl alloy.

The electronic structure of doped Fe–Ga alloy is investigated theoretically using methods of the density functional theory. The work aims to uncover the difference in the material's magnetostrictive properties when doping with transition metals or La as the simplest representative of rare-earth elements. The effect understudy was investigated by considering the change in two features of the electronic structure caused by doping: the density of d-states on Fe atoms and the nature of the Fe–Fe bonding near the doping atom. The transition metal atoms are surrounded by Fe atoms with a low-density d-states, eliminating the doping effect. The interatomic bonds of transition metals with the nearest Fe atoms have an antibonding character, while bonds between Fe atoms of the first and second coordination spheres are more binding than in an undoped alloy. This effect leads to magnetostriction decrease. In the La-doped alloy, the opposite picture is found. An increase in magnetostriction should occur due to the enhancement of the antibonding character of bonds between Fe atoms in the first and second coordination spheres of the dopant.

We report the critical behavior of the magnetization in Heusler alloy Co2TiGa0.8Sn0.2 as a potential candidate of high spin polarized materials with the characteristics of topological Weyl fermions. The Weyl semimetals are materials of great interest for applying spintronics devices, due to their unusual magnetoelectronic and magnetothermal properties. The magnetic properties of the synthesized Heusler alloy Co2TiGa0.8Sn0.2 are investigated around the Curie temperature TC. The magnetic isotherm measurements of Co2TiGa0.8Sn0.2 around TC exhibit that the critical exponent &#x03B4; is deduced to be 4.455(4) in high maximum applied field of 50 kOe and 4.823(9) in low maximum applied field of 10 kOe, respectively. Both &#x03B4; values are different from 3.0 derived by the conventional molecular field theory, but they are close to 5.0 predicted by the spin fluctuation theory for the itinerant electron ferromagnets. Possible origins for the discrepancy between experimental results and theoretical models are also discussed.

We report the magnetovolume effect of quaternary Heusler alloy CoFeCrAl as a potential candidate of spin gapless semiconductor. The crystal structure of CoFeCrAl was confirmed as the single phase of the ordered LiMgPdSn-type structure. From magnetization measurements at ambient pressure, the Curie temperature TC and the spontaneous magnetization Ms were determined to be 575.2 K and 2.01 &#x03BC; B/f.u., respectively. The TC is higher enough than room temperature and the Ms follows the Slater-Pauling rule. High-pressure magnetization measurements showed that the Ms is almost independent of applying pressures not only at 10 K but also up to 300 K, exhibiting that the electronic state of CoFeCrAl is fully spin polarized and it is preserved even at 300 K. The experimental results reveal that the quaternary Heusler alloy CoFeCrAl is an attractive material for functional electrode ferromagnets in spintronics devices.

To process ingots of Fe-Ga alloy single crystals into wafers, Fe-17% Ga alloy crystals were cut using multi-wire sawing or electric discharging and rolling. Further, their properties of magnetization and magnetostriction were analyzed using electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). It was observed that the magnetization and magnetostriction curves changed with increasing rolling reduction. Although magnetization was negligibly affected by deformation, the shape of the magnetostriction curve of the as-grown crystal could be modified by a slight reduction in rolling or a slight plastic deformation. EBSD results show that rolling introduced dislocations to form heterogeneous dislocation cell walls and decreased the surface roughness of the wafers. The pole figures obtained by XRD indicate that the samples were single crystals; however, the crystal orientation was different from the ideal orientation after rolling. Residual stress measurements using the cos α method revealed that compressive and tensile stresses remained in the polycrystalline surface layers of the samples cut by multi-wire sawing and electric discharging, respectively. Moreover, the stresses were affected by the tensile strains or magnetic fields when the residual stresses were relatively small in the sample. Although the magnetization and magnetostriction of a single crystal are affected by rolling, they are not significantly reduced by small rolling reductions.

Tensile tests and electron backscatter diffraction (EBSD) measurements were performed to understand the microscopic processes in the plastic deformation of Fe-17-at%-Ga alloy single crystals with a bodycentered cubic (BCC) structure. Samples close to the [001], [012], and [011] orientations for the tensile directions were cut from the alloy single crystal grown by the Czochralski method. They were plastically deformed at room temperature. The surface morphologies and microstructures of the deformed samples were characterized using an EBSD instrument attached to a scanning electron microscope. The mechanical properties such as elasticity and flow stress depended on the crystal orientation. Slip by dislocation glide was dominant in the tensile deformation in the [011]-oriented sample. Coarse planar deformation twins were observed in the [001]-oriented sample by plastic deformation. Thin deformation twins and slips were observed in the [012]-oriented sample. This implies that deformation twins have an important role in the plastic deformation of alloys. Although the addition of Ga induces solid solution hardening of iron-based alloys, the characteristic microscopic processes in the plastic deformations of the present alloys are similar to those in the plastic deformations of BCC iron and its alloys.

Procedure of determination of magnetic part of the specific heat of ferromagnetic (FM) solid from the results of the low-temperature measurements is proposed and applied to the number of non-stoichiometric Ni50Mn50-xInx alloys. It is shown that the disregard of magnetic contribution to the specific heat of FM solid results in the noticeable underestimation of Debye temperature and overestimation of the specific heat of electron subsystem of FM solid. The magnetic contribution to the low-temperature specific heat of antiferromagnetic (AFM) solid is negligibly small if Néel temperature exceeds the Debye temperature. In the opposite case the magnetic part of the specific heat of AFM solid may be comparable in value with non-magnetic part, but separation of these parts is an open problem.

<title>Abstract</title>Band-gap engineering is one of the fundamental techniques in semiconductor technology and also applicable in next generation spintronics using the spin degree of freedom. To fully utilize the spintronic materials, it is essential to optimize the spin-dependent electronic structures in the <italic>operando</italic> conditions by applying magnetic and/or electric fields. Here we present an advanced spectroscopic technique to probe the spin-polarized electronic structures by using magnetic circular dichroism (MCD) in resonant inelastic soft X-ray scattering (RIXS) under an external magnetic field. Thanks to the spin-selective dipole-allowed transitions in RIXS-MCD, we have successfully demonstrated the direct evidence of the perfectly spin-polarized electronic structures for the prototypical halfmetallic Heusller alloy <inline-formula><alternatives><tex-math>$$\hbox {Co}_2\hbox {MnSi}$$</tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mtext>Co</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> <mml:mtext>MnSi</mml:mtext> </mml:mrow> </mml:math></alternatives></inline-formula>. RIXS-MCD is a promising tool to probe the spin-dependent carriers and band-gap induced in the buried magnetic layers in an element specific way under the <italic>operando</italic> conditions.

Angle-resolved photoelectron spectroscopy utilizing soft x-ray synchrotron radiation was applied to Heuslertype Co2MnGa thin films that have a 1-nm Al capping layer. The bulk Fermi surfaces and band structures varied along the out-of-plane momentum, stemming from the three-dimensional crystal structure, in the absence of any in situ surface treatment. In addition, there were characteristic intersecting bands (Weyl cones), with crossing points near the Fermi level, which were consistent with computed results. TheWeyl cones are of bulk origin and are responsible for the high anomalous Nernst and the anomalous Hall coefficients. A close comparison of the experimental band structures in Co2MnGe and Co2MnGa indicated that the rigid band picture is valid in both alloys and that fine carrier tuning is possible by replacing Ga with Ge to improve the anomalous conductivity.

Type-II Na24Si136 clathrate octahedral single crystals surrounded by {111} facets were grown by evaporating Na from a molten mixture of Na4Si4 and Na9Sn4 at 823 K for 12 h. One of the obtained single crystals was used as a seed for the following single crystal growth of the type-II clathrate using the same method. The single crystal grown on the seed maintained the octahedral shape. The weight of the crystal grown with the seed was increased from 0.6 to 30.4 mg by repeating the seeded growth and was proportional to the surface area of the seed crystal.

Perpendicularly magnetized films exhibiting small saturation magnetizations (M s) are essential for spin-transfer-torque magnetoresistive random access memories (MRAMs). In this study, the intermetallic compound (Mn-Cr)AlGe with a Cu2Sb crystal structure was investigated as a material exhibiting lowM s (similar to 300 kA/m) and high-perpendicular magnetic anisotropy energy (K u). The layer thickness dependence ofK u and effects of Mg-insertion layers at the top and bottom (Mn-Cr)AlGe|MgO interfaces were studied for film samples fabricated onto thermally oxidized silicon substrates to realize highK u values in the thickness range of a few nanometers. The values ofK u were approximately7 x10 5 and2 x10 5J/m(3) at room temperature for 5 and 3nm-thick (Mn-Cr)AlGe films, respectively, with an optimum annealing temperature of 400 degrees C and Mg-insertion thicknesses of 1.4 and 3.0nm for the top and bottom interfaces, respectively. The Mg insertions were relatively thick compared with results of similar studies of the insertion effect on magnetic tunnel junctions. Cross-sectional transmission electron microscope images revealed that the Mg-insertion layers acted as barriers to the interdiffusion of Al atoms as well as oxidization from the MgO layers. TheK u at a few-nanometer thicknesses was comparable to or higher than those reported for perpendicularly magnetized CoFeB films, which are conventionally used in MRAMs, whereas theM s value was one third or smaller than those of the CoFeB films. The developed (Mn-Cr)AlGe films are promising materials because of their magnetic properties and their compatibility to the silicon process in film fabrication.

Atomic configuration at the equilibrium state, magnetic property and electronic state of CoVMnAl quaternary Heusler alloy were investigated by neutron diffraction, magnetic measurements, and first-principles calculations. Saturation magnetization measured at 5 K was quite small of 0.04 μ /f.u. for the specimen annealed at 873 K, and close to the expected value from the Slater-Pauling rule as predicted by Galanakis et al. (1983) [1]. Because the intensities of the superlattice diffractions of 111 and 200 were strong in the neutron diffraction, the atomic configuration of the CoVMnAl could be accurately determined. The best fitting was obtained as the L2 -type structure, in which the Co and Mn atoms randomly occupied the 8c site in the Wyckoff position in the space group number of 225. A small ferromagnetism was occurred in the specimen which was obtained by quenching at temperature above the order-disorder phase transition. The specimen exhibited a B2-like atomic configuration, where V and Al were partially distributed. Although the total energy in the LiMgPdSn-type ordered structure was 56 meV/f.u. lower than that in the L2 -type structure, the difference was small as the L2 -type structure would be obtainable in a finite temperature. B 1b 1b 1b

Substrate heating effects on the microstructure and magnetic properties of MnAlGe films grown on Si/SiO2 substrate by sputtering system were investigated. The MnAlGe film fabricated by low-temperature substrate heating demonstrated amorphous phase and paramagnetic property. The film of c-axis orientation associated with the Cu2Sb-type structure was obtained by sputtering at a substrate heating temperature of 270°C and it exhibited perpendicular magnetic anisotropy. From the magnetization curves measured at room temperature, the uniaxial magnetic anisotropy energy, Ku, was evaluated to be in the order of 106 erg/cm3, which is consistent with the literature, although the heating processing and temperature are slightly different. Microstructural observation indicated that the c-axis oriented grains were isolated in the matrix of the amorphous phase. The film lost the c-axis orientation at elevated substrate heating temperature, resulting in loss of the anisotropic magnetic property.

Magnetic thin films showing high perpendicular magnetic anisotropy, K-u, and low saturation magnetization, M-s, are essential for realizing a small switching current in spintronic devices utilizing the current induced magnetization switching phenomena. The Cu2Sb-type MnAlGe intermetallic compound is a material showing uniaxial magnetocrystalline anisotropy with a relatively low M-s, which is attractive for spintronic application. In this study, the layer thickness dependence of K-u was investigated in poly-crystalline MnAlGe films, and the MgO template effect is discussed to achieve perpendicularly magnetized films in a few-nanometer thickness range. Experimental results suggested that the (001)-texture for the perpendicular magnetization was promoted by the MgO(001) template through the solid-phase epitaxy growth by annealing, which is similar with that in conventionally used CoFeB|MgO layered samples. K-u of about 2 x 10(6) erg/cm(3) was achieved in a 5 nm-thick MnAlGe film using MgO buffer and capping exhibiting a low M-s value of approximately 200 emu/cm(3) at room temperature. Although the magnitude of K-u is still in a moderate range, the low M-s is a promising feature for spintronic application.

Combined accelerating effects of ¾¸ phase transformation by in-magnetic-field annealing and Zn-addition were investigated for Mn Zn Al in magnetic fields up to 15 T. The in-field annealing for Zn-added sample accelerated the ¾¸ transformation 16 times faster than Mn Al at annealing temperature of 623 K. The reduction of magnetization after finishing ¾¸ transformation was also more rapid than that of Mn Al . However, magnetic-field-induced acceleration of ¾¸ phase transformation and suppression of precipitation of ¢-phase were observed for Zn-added alloy Mn Zn Al annealed at 573 K. The obtained results suggested that the ¢-phase stabilized against both ¸- and ¾-phases by Zn-addition. Therefore, although the ¾¸ transformation was efficiently accelerated by in-field annealing of Mn Zn Al , more precisely control of annealing time is required for obtaining high fraction of ferromagnetic ¸-phase. 53 2 45 55 45 55 45 53 2 45 53 2 45

Ferromagnetic MnAlC (¸-phase) can be synthesized by a single-route conventional reactive sintering method. The maximum magnetization and coercivity were 75.8 Am /kg and 57 mT, respectively. The ¸-phase fraction was evaluated to be 81 mass% for Mn Al C annealed at 1273 K. The ¸-phase of Mn Al C can be synthesized at an annealing temperature from 873 to 1273 K, whereas that of Mn Al cannot be synthesized. It was indicated that the phase stability of the hcp-phase (¾-phase) was improved by adding carbon, resulting in an ¾¸ transformation. 2 55 45 2 55 45 2 55 45

Using a well-focused soft X-ray synchrotron radiation beam, angle-resolved photoelectron spectroscopy was applied to a full-Heusler-type Co2MnGe alloy to elucidate its bulk band structure. A large parabolic band at the Brillouin zone center and several bands that cross the Fermi level near the Brillouin zone boundary were identified in line with the results from first-principles calculations. These Fermi-level crossings are ascribed to majority spin bands that are responsible for electron transport with extremely high spin polarization especially along the direction perpendicular to the interface of magnetoresistive devices. The spectroscopy confirms there is no contribution of the minority spin bands to the Fermi surface, signifying half-metallicity for the alloy. Furthermore, two topological Weyl cones with band crossing points were identified around the X point, yielding the conclusion that Co2MnGe could exhibit topologically meaningful behavior such as large anomalous Hall and Nernst effects driven by the Berry flux in its half-metallic band structure.

Nitridation of Sm Fe powder was performed under a 5-T magnetic field for the temperature range 623–743 K to clarify the magnetic field effect on nitridation. Applying a magnetic field of 5 T promoted nitridation by approximately 0.6 nitrogen atoms per formula unit compared with zero-field nitrogenation, and almost fully-nitride Sm Fe N was obtained at 743 K. The magnetic field effect was discussed using a grain growth model based on magnetic properties of nitride-poor Sm Fe N (x < 3) phase and fully-nitride Sm Fe N phase. The obtained results show that in-field nitridation helps to synthesize nitride Sm Fe N system in the present condition. 2 17 2 17 2.9 2 17 x 2 17 3 2 17 3

The spin reorientation and Curie temperature of Mn Fe Sb Sn (0 ¯ x, y ¯ 0.15) compound were investigated by magnetization measurements. Spin reorientation temperature increased from 255 K at x = 0 to 383 K at x = 0.15, whereas it almost unchanged by Sn substitution. Curie temperature decreased down to 518 K with both Fe and Sn substitution. Substitution of Fe stabilized the ferrimagnetic state with magnetic moment lying in c-plane. Substitution of Sn induced the antiferromagnetic phase at low temperature. It was found that the magnetic hysteresis derived from quasi first-order magnetic phase transition exhibited at x 0.10 or T 300 K. 2 x x 1 y y 1 1 2 2

Nitrogenation of Sm Fe powder was performed under a zero field and a magnetic field of 5 T at 623, 673 and 743 K to clarify the magnetic field effect on nitrogenation. Applying a magnetic field of 5 T induced nitrogenation compared with zero-field nitrogenation, and almost fully nitride Sm Fe N was obtained at 743 K. Mössbauer spectroscopy results suggested that a 5-T magnetic field promoted the phase transformation to the fully-nitride Sm Fe N phase. The magnetic field effect was discussed based on the magnetic energy gain and magnetic properties of host Sm Fe and fully nitride Sm Fe N 2 17 2 17 2.9 2 17 3 2 17 2 17 3

X-ray powder diffraction, differential scanning calorimetry, and magnetization measurements were performed to investigate the effects of heat treatment on the magnetic and structural properties of as-cast and aging treated MnCoGe. The martensitic transformation temperature of the as-cast sample was 526 K for its first heating cycle, which decreased with repeating thermal cycles of 300–1273 K. MnCoGe prepared by aging treatment of 873 K for 7 days showed a first-order magnetic transition, which was accompanied by a martensitic transformation at 307 K. However, the transformation was not detected when the aging temperature was increased up to 973 K. The martensitic transformation temperature and volume of the parent phase was found to have a positive correlation.

Ferromagnetic exchange stiffness is a key to describe the robustness of a ferromagnetic interaction. Because the experimental determination of the exchange stiffness constant A continues to be elusive, especially at elevated temperatures, micromagnetic insights on the impact of thermal fluctuations on the ferromagnetic spin order have remained less tractable. In this study, the temperature dependence of A is experimentally determined for a Ni2Mn0.8In1.2 single crystal by measuring the 180 domain-wall width using off-axis electron holography and magnetocrystalline anisotropy. The theoretically expected power-law scaling with magnetization for A is shown to be applicable only in the low-temperature region (approximately half of the Curie temperature), and A starts to follow the power law with a significantly larger scaling exponent in the higher-temperature region. The decremental trends in the domain-wall width and the exchange length at elevated temperature seem to be attributed to this temperature dependence of A.

A nanoporous FePt alloy has been fabricated by dealloying a melt-spun Fe Pt B alloy composed of nanoscale amorphous and face-centered-cubic FePt (fcc-FePt) phases in H SO aqueous solution. The nanoporous alloy consists of single fcc-FePt phase with an Fe/Pt atomic ratio of about 55.3/44.7, and possesses a uniform interpenetrating ligament-channel structure with average ligament and pore sizes of 27 nm and 12 nm, respectively. The nanoporous fcc-FePt alloy shows soft magnetic characteristics with a saturation magnetization of 37.9 emu/g and better electrocatalytic activity for methanol oxidation than commercial Pt/C in acidic environment. The phase transformation from disordered fcc-FePt into ordered face-centered-tetragonal FePt (L1 -FePt) in the nanoporous alloy has been realized after annealing at 823–943 K for 600 s. The volume fraction of the L1 -FePt phase in the alloy increases with the rise of annealing temperature, which results in the enhancements of coercivity and saturation magnetization from 0.14 kOe and 38.5 emu/g to 8.42 kOe and 51.4 emu/g, respectively. The ligament size of the samples is increased after annealing. 60 20 20 2 4 0 0

Cu Sb-type intermetallic compound, MnAlGe, is known to exhibit uniaxial magnetocrystalline anisotropy and relatively small saturation magnetization, which is suitable for spintronic application, e.g. spin-transfer phenomena requiring small critical current density. Ge-concentration dependence of the crystal structures, saturation magnetization, M , and perpendicular magnetic anisotropy, K was investigated for MnAlGe films prepared onto silicon substrates with a thermally oxidized amorphous layer. For the stoichiometric and Ge-rich samples, the films exhibited (001)-texture with perpendicular magnetization. The maximum values of M and K were 270 emu/cm and 4.8 × 10 erg/cm , respectively, which were comparable values with those reported for bulk and epitaxially grown films in literatures. 2 s u s u 3 6 3

© 2019 Elsevier B.V. Substitution effects on weak itinerant electron ferromagnetism in Cr-based ternary alloy CrAlGe were investigated. It was found that substitution of Cr by 3d transition metal with more electrons than Cr enhanced the spontaneous magnetization and Curie temperature. In addition, the itinerancy of CrAlGe was suppressed with the increase of electrons. The ferromagnetism of CrAlGe was related to electron number rather than lattice parameters. The origin of change of itinerancy was suggested to be Coulomb force caused by effective nuclear charge.

© 1965-2012 IEEE. In-magnetic-field annealing (IFA) effects on Zn-modified Mn-Al and Mn-Al-C were investigated at the annealing temperature of 573 K, which was around their $_Rftxt-{\mathrm {C } }$. Mn53Zn2Al45 showed the magnetic-field-induced acceleration of the phase transformation to $\text{L}1-{0}$ -phase ( $\tau $ -phase) and the suppression of that to nonferromagnetic equilibrium phase. For Mn55Al45C2, IFA effects were not clearly detected. These different magnetic field effects were discussed by the difference of the mechanism in stabilization of $\tau $ -phase. It is found by a thermal analysis that the modification of Zn stabilized $\tau $ -phase against $\epsilon $ -phase, realizing acceleration of transformation to $\tau $ -phase. The addition of carbon stabilized $\epsilon $ -phase against $\tau $ -phase. The ineffectiveness of in-field annealing for Mn-Al-C is due to the stabilization of $\epsilon $ -phase and the reduction of the Curie temperature. The combination of Zn modification and IFA is realized to synthesize high fraction of $\tau $ -phase for short annealing time and low annealing temperature.

The magnetic properties and atomic arrangement of Mn2CoGa Heusler alloy were investigated experimentally and by theoretical calculations. The magnetic moment derived from spontaneous magnetization at 5K was 2.06 mu(B)/f.u. and was close to the integer number of the expected value from theoretical calculation and the Slate-Pauling rule predicted by Galanakis et al. The Curie temperature and L2(1)-B2 order-disorder phase transition temperature were 741 and 1047 K, respectively. Powder neutron diffraction experiment results suggested that the atomic arrangement prefers an L2(1b)-type structure rather than that of Hg2CuTi, being consistent with our previous results of high-angle annular dark-field-scanning transmission electron microscopic observations. The magnetic moments obtained were in good agreement with the theoretical values in the model of the L2(1b)-type structure. The density of states obtained by the first-principles calculation combined with the coherent potential approximation in Mn2CoGa with the L2(1b)-type crystal structure maintained the half-metallic character, even though disordering by Mn and Co atoms was introduced.

© 2019 The Japan Institute of Metals and Materials. An in-field heat treatment furnace utilized for a magnet with a 50 mm room-temperature bore was made to study magnetic field effect on gas-solid reaction. Using this furnace, nitridation of Sm2Fe17 powder was performed under a 5-T magnetic field and a 0.1-MPa nitrogen gas pressure for the temperature range 623 to 743 K. Applying a magnetic field of 5 T promoted nitridation by approximately 0.6 nitrogen atoms per formula unit compared with zero-field nitridation, and almost fully nitride Sm2Fe17N2.9 was obtained at 743 K.

© 2018 Author(s). Cu-substitution effects on ferromagnetism in Cr-base ternary alloy CrAlGe with an orthorhombic TiSi2-type structure was investigated. The lattice parameters of Cr0.95Cu0.05AlGe were a = 4.748 Å, b = 8.209 Å and c = 8.696 Å at room temperature. The spontaneous and effective moment were determined to be ps = 0.533 μB/f.u at 5 K and peff = 1.89 μB/f.u, respectively. The Curie temperature TC was estimated to be 108 K. These ps and TC of Cr0.95Cu0.05AlGe were larger than those of CrAlGe and Ti-substituted compound. The peff/ps was determined to be 3.55, which was smaller than that of CrAlGe and Ti-substituted compound. Obtained results suggest that the substitution of Cu for Cr in CrAlGe leads suppression of its weak itinerant electron ferromagnetism.

© 2018 Author(s). The magnetic properties of Mn1-xTMxAlGe (TM = V, Fe and Cu) were investigated for x ≤ 0.2. The spontaneous magnetization decreased with increasing x. A remarkable decrease in the Curie temperature TC was observed for TM = Fe. For ferromagnetic MnAlGe (x = 0) and TM = nonmagnetic Cu (x = 0.2), Curie-Weiss law was confirmed. The compounds with TM = V and Fe (x = 0.2) did not show Curie-Weiss law, and the data of reciprocal susceptibility vs. temperature bent, indicating change of the magnetism from ferromagnetism. Obtained results suggested that the magnetic moments of V and Fe were aligned antiparallel to those of Mn, resulting in the ferrimagnetism-like behavior.

© 2018 Elsevier B.V. The magnetic and structural properties of Mn1−xCrxAlGe (0 ≤ x ≤ 1.0) compounds were investigated. The spontaneous magnetization Ms and Curie temperature TC of Mn1−xCrxAlGe has a cusp at x = 0.2. The maximum values of Ms and TC are 1.74 μB/f.u. and 601 K, respectively. It was found that the tetragonal Cu2Sb-type structure was stable for 0 ≤ x ≤ 0.75, whereas orthorhombic TiSi2-type structure was observed for x ≥ 0.8. The reciprocal susceptibility as a function of temperature suggested that the magnetic moment of Cr is antiferromagnetically coupled with that of Mn in Cu2Sb-type structure.

© 2018 Elsevier B.V. The magnetic field effect on the reactive sintering process of MnBi was investigated. Magnetic-field-induced enhancement of the reaction was found to be exhibited at the initial stages. The coercivity field decreased with an increase in the in-field annealing time. The kinetics of the reaction were in good agreement with the diffusion-controlled reaction model. It is suggested that the decrease in activation energy at the initial stages of reaction increased the amount of formed MnBi phases, resulting in enhancement of the reaction Mn + Bi to MnBi phase by in-field reactive sintering.

We investigated temperature dependence of differential conductance G(V) in planar junctions consisting of Co-based Heusler alloy Co2TiSn and superconductor Pb. Ferromagnetic Co2TiSn was predicted to be half-metal by first-principles band calculations. The spin polarization P of Co2TiSn was deduced to be 60.0% at 1.4K by the Andreev reflection spectroscopy. The G(V) spectral shape was smeared gradually with increasing temperature and its structure was disappeared above the superconducting transition temperature Tc. Theoretical model analysis revealed that the superconducting energy gap Δ was 1.06meV at 1.4K and the Tc was 6.8K, indicating that both values were suppressed from bulk values. However, the temperature dependent Δ(T) behavior was in good agreement with that of the Bardeen-Cooper-Schrieffer (BCS) theory. The experimental results exhibit that the superconductivity of Pb attached to half-metallic Co2TiSn was kept the conventional BCS mechanism characterized strong-coupling superconductors while its superconductivity was slightly suppressed by the superconducting proximity effect at the Co2TiSn/Pb interface.

Precise magnetization measurements of a half-metallic ferromagnet Co2TiSn with the Heusler type structure have been carried out under pressure up to 1.27 GPa. At ambient pressure, the spontaneous magnetic moment Msexp and the Curie temperature TCexp are experimentally obtained to be 1.993(3)μB/f.u. and 376.76(7) K, respectively. The Msexp is independent of applying pressure. The TCexp decreases with the increase of pressure and the pressure derivative of the Curie temperature dTCexp/dp is estimated to be -3.15(9) K/GPa. Furthermore, the pressure effect on the electronic and magnetic properties of Co2TiSn has been theoretically investigated on the basis of first-principles density functional calculations by using the projector augmented wave method in order to evaluate the half metallicity of Co2TiSn. Both the experimental and the theoretical results under pressure reveal that Co2TiSn is half metal. The experimental results of pressure-dependent magnetic properties are finally discussed on the basis of the spin fluctuation theory for itinerant electron magnetism.

We have studied the electronic structure of ferrimagnetic Mn2VAl single crystals by means of soft x-ray absorption spectroscopy (XAS), x-ray absorption magnetic circular dichroism (XMCD), and resonant soft x-ray inelastic scattering (RIXS). We have successfully observed the XMCD signals for all the constituent elements. The Mn L2,3 XAS and XMCD spectra are reproduced by spectral simulations based on density-functional theory, indicating the itinerant character of the Mn 3d states. On the other hand, the V 3d electrons are rather localized since the ionic model can qualitatively explain the V L2,3 XAS and XMCD spectra. This picture is consistent with local dd excitations revealed by the V L3 RIXS.

© 2018 The Japan Institute of Metals and Materials. The magnetic and structural properties of ferrimagnetic (FRI) Mn1.9Fe0.1Sb0.9Sn0.1 with a Cu2Sb-type tetragonal structure were studied by magnetization and high field X-ray diffraction (XRD) measurements in 10 ≤ T ≤ 773 K and in magnetic fields μ0H up to 5 T. The lattice parameters a and c at 285 K were estimated to be 0.407 nm and 0.655 nm, respectively. The saturation magnetization at 10 K was determined to be 39.1 Am2/kg. It was observed that a first order magnetic transition (FOMT) with a thermal hysteresis occurred in the vicinity of 310 K under low magnetic fields. This FOMT disappeared easily by applying magnetic fields over 0.4 T.

The Pressure effect on the magnetic properties of the weak itinerant electron ferromagnet CrAlGe was investigated at pressures up to 1.0 GPa. The spontaneous magnetic moment p(s) and Curie temperature T-C decreased with increasing applied pressure P. The pressure derivatives of p(s) and T-C were dp(s)/dP = -3.98 x 10(-5) mu(B)/MPa and dT(C)/dP = -6.58 x 10 K-3/MPa, respectively. These obtained results are discussed on the basis of Takahashi's spin fluctuation theory for weak itinerant electron ferromagnets. The characteristic parameters T-0 and T-A increased with pressure.

We have investigated phase stabilities and magnetic properties of the tetragonal D0(22) phase in Mn-deficient Mn3-xGa and Ge-substituted Mn3Ga1-yGey. A transition from the D0(22) to L1(0) phase is observed in the composition range of x = 0.5-0.8 in Mn3-xGa. On the other hand, the D0(22) phase is confirmed in the overall composition of Mn3Ga1-yGey. The thermal stability of the D0(22) phase strongly depends on the Ge content compared with the Mn deficiency. Magnetization of Mn3-xGa is increased by introducing the Mn deficiency, whereas that of Mn3Ga1-yGey decreases with increasing Ge content despite a constant number of Mn atoms. This result suggests that the magnitude of magnetic moment of Mn atom in Mn3Ga1-yGey is influenced by variations of valence electron and structural properties caused by the Ge substitution.

Temperature dependences of the electrical resistivity have been measured on the Heusler alloy system Ni2MnGa1-xFex. The phase diagram of Ni2MnGa1-xFex was constructed on the basis of the experimental results. The structural and magnetic transition temperatures are consistent with those previously determined by magnetic measurements. The changes of the electrical resistivity at the martensitic transition temperature Delta rho, were studied as a function of Fe concentration x. The Delta rho abruptly increased in the concentration range between x = 0.15 and 0.20. The magnetostructural transitions were observed at x = 0.275, 0.30, and 0.35.

Specific heat measurements were performed at low temperatures for Ni50Mn50-xInx alloys to determine their Debye temperatures (theta(D)) and electronic specific heat coefficients (gamma). For x <= 15, where the ground state is the martensite (M) phase, theta(D) decreases linearly and gamma increases slightly with increasing In content. For x >= 16.2, where the ground state is the ferromagnetic parent (P) phase, gamma increases with decreasing In content. Extrapolations of the composition dependences of theta(D) and gamma in both the phases suggest that these values change discontinuously during the martensitic phase transformation. The value of theta(D) in the M phase is larger than that in the P phase. The behavior is in accordance with the fact that the volume of the M phase is more compressive than that of the P phase. On the other hand, gamma is slightly larger in the P phase, in good agreement with the reported density of states around the Fermi energy obtained by the first-principle calculations.

The transformation behaviors on metamagnetic shape memory Ni46.4Mn38.8In12.8Co2.0 film were investigated by X-ray diffraction experiments in the temperature up to 473 K and magnetic fields mu H-0 up to 5 T. The prepared film showed the parent phase with L2(1) structure at 473 K, and with preferred orientation along the 111 plane. The magnetic field induced reverse transformation was directly observed at T = 366 K, which was just around the reverse transformation starting temperature.

The phase formation of ferromagnetic L1(0)-MnAl (tau-phase) was accelerated by annealing in magnetic field. With in-field annealing at 623 K, the magnetization of the t-phase annealed at 15 T was a maximum of 72.2 A.m(2)/kg at 1.5 T, which is over 4 times larger than that annealed without an external magnetic field for the same annealing time. On the other hand, the transformation from tau-phase to beta-phase was suppressed under magnetic field. The obtained bulk sample did not show magnetic anisotropy because of the epsilon-tau solid-state transformation. Obtained results suggested that magnetic field induced acceleration of transformation was due to the gain of Zeeman energy, which increases the driving force of the epsilon-tau transformation.

Magnetic properties for CrAlGe with an orthorhombic TiSi2-type structure were investigated under ambient pressure and hydrostatic pressure. CrAlGe is ferromagnetic at the temperature below Curie temperature TC of 80 K and has the spontaneous magnetic moment ps of 0.41 mu B/f. u. at 5 K and the effective moment peff of 1.89 mu B/f. u. under ambient pressure. For the temperature T below 30 K, the decrease in p(s)(T)(2)/p(s)(5K)2 was proportional to T 2. However, the decrease in p(s)(T)(2) /p(s)(5K)(2) was proportional to T-4/3 for 30 K < T < T-C. The ratio peff/ps was consistent with the theoretical curve of the generalized Rhodes- Wohlfarth plot (Takahashi plot). Obtained results suggest that CrAlGe is a weak itinerant electron ferromagnet. By applying a high pressure of 1 GPa, TC decreased by approximately 10 K.

The substitution effect on half-metallicity for Co-based Heusler alloys Co2TiGa1-xSnx was investigated by experimental measurements and first-principles band calculations. The synthesized alloys crystalized in the ordered L2(1) crystal structure. The spontaneous magnetization obeyed the Slater-Pauling rule, indicating the possibility that Co2TiSn and Co2TiGa0.5Sn0.5 are half-metals. The first-principles band calculations revealed that Co2TiSn is half-metal and Co2TiGa0.5Sn0.5 is nearly half-metal. The spin polarization P was determined by the Andreev reflection technique. The intrinsic P values were 58.9% for Co2TiSn and 58.2% for Co2TiGa0.5Sn0.5, respectively. The P values of Co2TiGa1-xSnx were relatively higher than other Co-based Heusler alloys. Thus, Co-based Heusler alloys Co2TiGa1-xSnx are possible candidates for half-metallic electrode materials in spintronic devices.

Crystal structure, magnetization and magnetic susceptibility have been studied for the La1-xTbxMn2Si2 (0 &lt;= x &lt;= 1) polycrystalline and quasi-single crystalline samples. It has been shown that, at low temperature T =4.2 K, substitution of the terbium for lanthanum leads to recurred change of the type of interlayer Mn-Mn magnetic ordering. For the compounds with x &lt; 0.2 approximate to x(cl) the manganese magnetic moments of adjacent layers are ordered ferromagnetically, in the concentration range 0.2 &lt;x &lt;x(c2) (the critical concentration x(c2) is between 0.4 and 0.6) the antiferromagnetic order is realized, while for x&gt; x(c2) the Mn sublattice is again ferromagnetically ordered and, due to the negative Tb Mn interaction, ferrimagnetic structure is formed. Using the magnetization data, the concentration magnetic phase diagram has been suggested. The observed variation of the type of magnetic ordering has been explained in terms of the change of interatomic Mn-Mn distances and a competition of the Tb-Mn, Mn-Mn and Tb-Tb interlayer exchange interactions. (C) 2016 Elsevier B.V. All rights reserved.

Microstructural analysis was performed for Mn-Bi prepared by in-field solid-phase reactive sintering, in order to investigate the origin of magnetic field effects on the reaction. The number of formed MnBi phase around Mn grain in 10 T was almost 3 times larger than that in a zero field. The results indicated that the magnetic field enhanced the phase formation rate of MnBi phase. Due to the enhancement of the phase formation rate, the fraction of MnBi phase was drastically increased by in-field annealing.

Magnetic and structural properties of Sn- substituted Mn2Sb were investigated. A first-order magnetic transition (FOMT) from a ferrimagnetic (FRI) to an antiferromagnetic state occurred between 100 and 200 K, which was accompanied by an iso-structural transformation. Upon cooling in 5 T, the residual FRI phase was observed even at 10 K, and the residual FRI phase slightly decreased with increasing time. The results indicate that the FOMT of Mn2Sb0.9Sn0.1 is arrested by applying a magnetic field.

The substitution effect on half-metallicity for Co-based Heusler alloys Co2TiGa1-xSnx was investigated by experimental measurements and first-principles band calculations. The synthesized alloys crystalized in the ordered L2(1) crystal structure. The spontaneous magnetization obeyed the Slater-Pauling rule, indicating the possibility that Co2TiSn and Co2TiGa0.5Sn0.5 are half-metals. The first-principles band calculations revealed that Co2TiSn is half-metal and Co2TiGa0.5Sn0.5 is nearly half-metal. The spin polarization P was determined by the Andreev reflection technique. The intrinsic P values were 58.9% for Co2TiSn and 58.2% for Co2TiGa0.5Sn0.5, respectively. The P values of Co2TiGa1-xSnx were relatively higher than other Co-based Heusler alloys. Thus, Co-based Heusler alloys Co2TiGa1-xSnx are possible candidates for half-metallic electrode materials in spintronic devices.

The magnetic properties of ferrimagnetic Mn1.9Fe0.1Sb0.9Sn0.1 with a Cu-2 Sb-type tetragonal structure were investigated in the temperature range 10 to 360 K and in magnetic fields up to 5 T. The lattice parameters a and c were estimated to be 0.407 and 0.655 nm, respectively, at 293 K. The saturation magnetization at 10 K was 39.1 A.m(2)/kg (1.62 mu B per formula unit), which was slightly smaller than the value at 75 K, and the magnetization showed thermal hysteresis between 70 and 230 K. The compound showed a first-order magnetic transition from the ferrimagnetic to a paramagnetic-like state with a thermal hysteresis in the vicinity of 320 K. The results are discussed on the basis of the ferrimagnetic and antiferromagnetic transitions and spin reorientation.

Metamagnetic shape memory alloy (MMSMA), in which the martensitic transformation temperature can be controlled by a magnetic field, is a new type of magnetic shape memory material. In MMSMAs, because unique physical properties, such as giant magnetoresistance, giant magneto-thermal conductivity and inverse magnetocaloric effects, are observed to be associated with the martensitic transformation, these materials are good candidates for application as actuators and sensors acting in mixed external fields of temperature, stress and magnetic field. In the present Viewpoint, some interesting and unique properties in the MMSMAs are introduced, and some criteria of materials design for practical use are discussed. (C) 2016 Elsevier Ltd. All rights reserved.

The magnetic and structural properties of ferromagnetic MnCo0.92Fe0.08Ge were investigated by magnetization and X-ray powder diffraction measurements in magnetic fields up to 5 T. The compound showed first-order transition between the paramagnetic and ferromagnetic state with a thermal hysteresis of approximately 24 K, which was accompanied by the martensitic transformation from the hexagonal Ni2In-type structure to the orthorhombic TiNiSi-type structure in the vicinity of 275 K. The cell volume expanded by 4.1% during the martensitic transformation. The magnetic moment of MnCo0.92Fe0.08Ge was estimated to be 111 Am(2)kg(-1) (3.7 mu(B)/f.u.) at 10 K. The compound showed both metamagnetic transition and magnetic field-induced martensitic transformation.

Magnetic fields effects on liquid-phase reaction sintering on MnBi were investigated. The liquid-phase reaction was so fast even in a zero field that the fraction of in-field sintered ferromagnetic MnBi phase was independent of the external magnetic field. However, the ferromagnetic MnBi crystals in the in-field sintered sample were oriented along the external magnetic field direction. The Lotgering factor of the infield sintered sample was 0.99. This result indicated that almost completely anisotropic MnBi phase could be obtained by in-field liquid phase reactive sintering. (C) 2015 Elsevier B.V. All rights reserved.

Phase equilibria at 800, 900 and 1000 degrees C, as well as order-disorder and magnetic transitions of Heusler-type ordered phase were investigated in the Co-Mn-Ga ternary system. The beta phase with bcc structure including the Heusler-type ordered phase exists in a wide composition range of the ternary system. It was confirmed by STEM-HAADF observation that the crystal structure of the Heusler-type ordered alloy Mn2CoGa is L2(1b)-type Fm (3) over barm (i.e., (Mn,Co)(2)MnGa), but not inverse-Heusler (Hg2CuTi) type F (4) over bar 3m. The L2(1)/B2 order-disorder transition temperature shows a maximum at the stoichiometric composition of Co2MnGa and the Curie temperature of the L2(1) phase decreases with increasing Ga content. Magnetic moments converted from magnetization curves at 4.2 K for CoxMn(76-x)Ga24 alloys well follow the generalized Slater-Pauling rule in the composition of 25 &lt;= x &lt;= 50, and magnetization curves indicate very small high-field magnetic susceptibility. (C) 2015 Elsevier B.V. All rights reserved.

We have unravelled the electronic structure of a class of metamagnetic shape memory alloy Ni2Mn1+xIn1-x by combining bulk-sensitive hard x-ray photoelectron spectroscopy and first-principles density-functional calculations. A sharp drop in the Ni 3d e(g) density of states forming a pseudogap in the martensitic phase transition (MPT) for x = 0.36 has been observed near the Fermi level. As a feature of MPT, hysteretic behaviour of this drop has been confirmed in both cooling and warming. This pseudogap is responsible for the giant negative magnetoresistance. The experimental result is well reproduced by the first principle calculation. We have also clarified theoretically that the MPT is linked to a competition of ferromagnetic and anti-ferromagnetic coupling between ordinary and anti-site Mn atoms.

Electronic, magnetic, and thermodynamic properties of Co2Cr(Ga,Si)-based shape-memory alloys, which exhibit reentrant martensitic transformation (RMT) behavior, were studied experimentally. For electric resistivity (ER), an inverse (semiconductor-like) temperature dependence in the parent phase was found, along with anomalous behavior below its Curie temperature. A pseudobinary phase diagram was determined, which gives a "martensite loop" clearly showing the reentrant behavior. Differential scanning calorimetry and specific-heat measurements were used to derive the entropy change Delta S between martensite and parent phases. The temperature dependence of the derived Delta S was analyzed thermodynamically to confirm the appearances of both the RMT and normal martensitic transformation. Detailed studies on the specific heat in martensite and parent phases at low temperatures were also conducted.

© 2015 The Authors. Published by Elsevier B.V. Structural and magnetic properties of Cr-based compound CrAlGe were investigated. The crystal structure was found to be an orthorhombic TiSi2-type with lattice parameters a = 0.4770 nm, b = 0.8254 nm and c = 0.8725 nm at room temperature. Magnetization curve of CrAlGe showed the ferromagnetic behavior. The saturation magnetic moment, spontaneous magnetic moment and Curie temperature of CrAlGe were determined to be 0.45 μB/f.u., 0.41 μB/f.u. and TC = 80 K, respectively. For the temperature T below 30 K, the decrease in the square of the spontaneous magnetization M0(T)2 was proportional to T2. However, for 30 < T < TC, the decrease in M0(T)2 was proportional to T4/3. Obtained results suggest that CrAlGe is a weak itinerant electron ferromagnet.

We report on the first study of magnetic and structural properties of Co2Fe1-xTixGa thin films prepared by a magnetron sputtering technique. The presence of well-defined (220) and (422)peaks corresponding to the principal reflection of the Heusler structure were revealed by XR Danalysis. Results of magnetic properties measurements of the thin films showed that annealedsamples have uniaxial in-plane anisotropy but magnetic properties of as-prepared samples exhibitanisotropy within the plane. The annealed thin films demonstrate complex magnetization process which can be attributed to the difference in the magnetic properties of two coexisting phases withB2 and L21 structural ordering.

Ferromagnetic MnBi was synthesized by a solid-state reaction sintering method in high magnetic fields up to 15 T. The fraction of ferromagnetic MnBi phase in the sample sintered at 15 T was about 70% by weight, which was much larger than that sintered in a zero magnetic field. It was found that high magnetic fields dramatically enhanced the formation of MnBi phase from bismuth and manganese. In addition, the c-axis of a hexagonal structure of MnBi was oriented parallel to the magnetic field direction. These magnetic field effects on the synthesizing process were examined based on the gain of the Zeeman energy and the uniaxial magnetic anisotropy of MnBi phase. © 2014 Published by Elsevier B.V.

In order to investigate behavior of magnetic field-induced reverse martensitic transformation for Ni-Co-Mn-Sb, magnetization experiments up to a static magnetic field of 18 T and a pulsed magnetic field of 40 T were carried out. In the thermomagnetization curves for Ni41Co9Mn39Sb11 alloy, the equilibrium transformation temperature T-0 was observed to decrease with increasing applied magnetic field, H-0, at a rate of dT(0)/d(0)H = 4.6 K/T. The estimated value of entropy change evaluated from the Clausius-Clapeyron relation was about 14.1 J/(Kkg), which was in good agreement with the value obtained by differential scanning calorimetric measurements. For the isothermal magnetization curves, metamagnetic behavior associated with the magnetic field-induced martensitic transformation was observed. The equilibrium magnetic field, H-0(0) = (H-0(Af) + H-0(Ms))/2, of the martensitic transformation tended to be saturated at lower temperature; that is, transformation arrest phenomenon was confirmed for the Ni-Co-Mn-Sb system, analogous with the Ni(Co)-Mn-Z (Z = In, Sn, Ga, Al) alloys. Temperature dependence of the magnetic field hysteresis, H-0(hys) = H-0(Af) - H-0(Ms), was analyzed based on the model for the plastic deformation introduced by the dislocations. The behavior can be explained by the model and the difference of the sweeping rate of the applied magnetic field was well reflected by the experimental results.

Structure, lattice parameters, spontaneous magnetization (I-s), and the Curie temperature (T-C) of MnAlGe and MnGaGe compounds with the Cu-2 Sb-type structure and their substituted compounds were investigated. Cr substitution for Mn enhanced I-s and T-C, whereas Fe substitution for Mn degraded them. These behaviors are in accord with the previously reported results, and are also common to the MnGaGe compound series. For MnAlGe, lattice parameter a increases by 0.2% and 0.4% for Cr and Fe substitution, while c changes by +0.1% and -1.3%, respectively. For MnGaGe, a decreases by 0.08% for Cr and increases by 0.2% for Fe substitution, while c changes by + 0.5% and -1.0%, respectively. T-C tended to increase with increasing length of c, suggesting that the interlayer distance between Mn layers is a key factor related to the height of T-C, i.e., the strength of the magnetic exchange interaction.

A powder sample of body-centered tetragonal Ni2N in a single phase was prepared by a high rate-type triode dc reactive sputtering and the magnetic properties have been reinvestigated It is confirmed that Ni2N is not a ferromagnet. However, the material is not a simple paramagnet either and shows a weak spin-glass-like behavior at low temperatures with a freezing temperature of about 8 K. Posible origins of the behavior are discussed. Band-structure calculations are reported to see the stability of the nonmagnetic ground state of bct Ni2N against lattice expansion and appearance of nitrogen vacancies. (C) 2014 Elsevier B.V. All rights reserved.

The field-induced entropy change and the magnetocaloric effect (MCE) of the ferromagnetic shape memory alloys Ni2Mn1-xCuxGa and Ni2Mn1+xIn1-x are studied theoretically on the basis of a phenomenological free energy. The free energy is expanded in powers of the mangetization M and the tetragonal distortion e(3), which are the order parameters for the ferromagnetic and martensitic transitions, respectively. Through the magneto-structural interaction term in the free energy, magnetic fields can affect also e(3) to shift the martensitic first-order transition temperatures. This shift of the transition temperature results in large field-induced changes in the order parameters, which can be responsible for large MCEs. It is found that the resulting MCEs depend on the nature of the magnetostructural interaction. In Ni2Mn1-xCuxGa with the attractive magneto-structural interaction, magnetic fields cause the negative entropy change as in the normal MCE. In Ni2Mn1+xIn1-x with the repulsive interaction, on the other hand, magnetic fields can do the positive entropy change causing the inverse MCE. For both the alloy systems, the x dependences of the refrigerant capacity (RC) are studied to find the compositions optimum for large MCEs. Applicability of the Maxwell relation to the system with the first-order transition is also studied by simulating the held-induced entropy changes on the basis of the Maxwell relation. (C) 2014 Elsevier B.V. All rights reserved.

Thermal strain, permeability, and magnetization measurements of the ferromagnetic shape memory alloys Ni50+xMn27-xGa23 (x = 2.0, 2.5, 2.7) were performed. For x = 2.7, in which the martensite transition and the ferromagnetic transition occur at the same temperature, the martensite transition starting temperature T-Ms shift in magnetic fields around a zero magnetic field was estimated to be dT(Ms)/dB = 1.1 +/- 0.2 K/T, thus indicating that magnetic fields influences martensite transition. We discussed the itinerant electron magnetism of x = 2.0 and 2.5. As for x = 2.5, the M-4 vs. B/M plot crosses the origin of the coordinate axis at the Curie temperature, and the plot indicates a good linear relation behavior around the Curie temperature. The result is in agreement with the theory by Takahashi, concerning itinerant electron ferromagnets.

Permeability and differential scanning calorimetry measurements were carried out on Ni2MnGa1-xFex (0 &lt;= x &lt;= 0: 40). On the basis of the experimental results, the phase diagram in the temperature-concentration plane was determined. The characteristics of the determined phase diagram are similar to those of the phase diagrams of Ni2+xMn1-xGa, Ni2Mn1-xCuxGa and Ni2MnGa1-xCux systems, where the magneto-structural transition between the paramagnetic austenite phase (Para-A) and ferromagnetic martensite phase (Ferro-M) occurs. Furthermore, the concentration dependence of the magnetic moment per formula unit, mu(s), at 5 K for Ni2MnGa1-xFex (0 &lt;= x &lt;= 0.375) is also reported. (C) 2013 Elsevier B.V. All rights reserved.

The structural and magnetic properties of Heusler alloy Ni46Mn41In13 were studied by magnetization and X-ray powder diffraction measurements in the 4.5-350 K temperature range and in magnetic fields up to 5 T. The alloy undergoes martensitic transformation from a L2(1)-type cubic structure with alpha(c) = 0.600 nm at 293 K to a six-layered monoclinic (6M) structure in the transition temperature of 160-230 K. The lattice parameters for the 6M structure were estimated to be a(m) = 0.441 nm, b(m) = 0.557 nm, c(m) = 1.30 nm, alpha(m) = 90.0 degrees, beta(m) = 94.0 degrees, and gamma(m) = 90.0 degrees at 75 K. In this transformation from the L2(1) to 6M structures, the cell volume contracts by 0.34% at 8 K. In addition, we observed the magnetic field-induced reverse transformation of this alloy.

The phase diagram, magnetic properties and the region over which the Heusler alloys Co2Cr(Ga1 xSix) occur as a single phase have been established. A single phase was obtained in the composition range of x &lt;= 0.5, in which the order-disorder phase transition temperature from the L2(1) to the B2 phase, T-t(L21/B2), increased almost linearly with increasing x. The value of T-t(L21/B2) for the L2(1)-type Co2CrSi Heusler alloy, estimated by linear extrapolation from its concentration dependence, was about 1450 K, and therefore higher than that of Co2CrAl and Co2CrGa. The Curie temperature, T-C, also increased with increasing x becoming 600 K at x = 0.5, thus reflecting an increase in the magnetic moment caused by the change in the number of the valence electrons. The concentration dependence of the spontaneous magnetic moment, M-s, measured at 5 K increased with increasing x, almost following the generalized Slater-Pauling (S. P.) rule predicted by Galanakis et al. (C) 2013 Elsevier B. V. All rights reserved.

Magnetization measurements have been carried out on the magnetic shape memory alloys (MSMAs) Ni2Mn1.44-xCuxSn0.56 (0 &lt;= x &lt;= 0.09). On the basis of the experimental results, the phase diagram of Ni2Mn1.44-xCuxSn0.56 (0 &lt;= x &lt;= 0.09) alloys in the temperature-concentration plane has been determined. The resultant phase diagram is spanned by paramagnetic austenite (Para-A), ferromagnetic austenite (Ferro-A) and ferromagnetic martensite (Ferro-M) phases. The martensitic transition temperature T-M makes a broad maximum as a function of x, whereas, in the austenite phase the Curie temperature T-C decreases slightly with x. The T-C of Ni2Mn1.415Cu0.025Sn0.56 was found to decrease linearly with pressure, whereas TM increased linearly with pressure. The values of dT(M)/dp and dT(C)/dp of Ni2Mn1.415Cu0.025Sn0.56 were found to be 0.88 K/kbar and -0.31 K/kbar, respectively. (C) 2013 Elsevier B.V. All rights reserved.

The structure, thermal stability and magnetic properties of melt-spun Fe55Pt25B20-xPx (x = 0-5) alloys have been investigated. Addition of P increases the amorphous-forming ability of an Fe55Pt25B20 alloy, leading to the formation of the full amorphous phase. After annealing, the homogeneous nanosized structure consisting of hard L1(0)-FePt and soft Fe2B magnetic phases with average grain size of similar to 40 nm are obtained for the alloys with x = 0 and 2, while a L1(0)-FePt/Fe2B nanocomposite structure with an average grain size of similar to 80 nm is obtained for the alloy with x = 5. As the P content increases, the coercivity (H-i(c)) of the L1(0)-FePt/Fe2B nanocomposite alloys significantly increases, the remanence (B-r) decreases. The alloy with x = 5 shows the largest H-i(c) of 12.1 kOe, while the alloy with x = 2 exhibits higher B-r of 53.5 emu/g and better demagnetization curve squareness, which is due to the enhancement in exchange coupling among the uniformly distributed nanosized Fe2B and L1(0)-FePt phases. (C) 2012 Elsevier B. V. All rights reserved.

Magnetic, magnetooptical and magnetotransport properties of Co50.3Fe20.3Ti5.6Ga23.8 thin films were studied for the as-prepared as well as annealed samples. Measurements of transverse magnetooptical Kerr effect revealed that the spectral response of the films strongly depends on the structural ordering which can be manipulated by annealing conditions. Peculiarities in the magnetic properties of the films were attributed to the coexisting phases with different degree of structural disorder. Magnetoresistance of Co50.3Fe20.3Ti5.6Ga23.8 thin films was found to be linear in the fields above 1 T which is typical for half-Heusler systems as well as for Heusler-based ferromagnetic shape memory alloys.

The martensitic transformation behavior in a Ni45Co5Mn36In14 was investigated at low temperatures. Almost perfect superelasticity was confirmed below 200 K. The reverse transformation finishing stress monotonically decreased with decreasing temperature and the forward transformation starting stress changed from a decrease to an increase at similar to 125K. The temperature dependence of equilibrium stress had the same tendency as that of equilibrium magnetic field, allowing the thermal transformation arrest temperature to be determined. The temperature dependence of hysteresis in stress-induced transformation was also similar to that in magnetic-field-induced transformation, and the levels of dissipation energy yielded by the stress and magnetic field were intrinsically equivalent. (C) 2013 AIP Publishing LLC.

We present the magnetic properties and the magnetic phase diagram of Ni50Mn50-xGax ferromagnetic shape memory alloys across a wide concentration range. Martensitic transformation, intermediate transformation, B2 L21 order disorder transformation, Neel and Curie temperatures are determined for the prepared samples. The martensitic transformation temperature decreases with increasing Ga concentration and bends two times when crossing the Curie temperature and the intermediate-phase transformation temperature. Spontaneous magnetization and its composition dependence were also investigated. Composition dependence of the transformation temperatures and the spontaneous magnetization in the martensite phase of NNi50Mn50-xGax are compared with those of Ni50Mn50-xGaxIn, and Ni50Mn50-xGax, revealing a similarity in the NiMn-based alloy systems. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Normally, shape memory effect (SME) is obtained by the reverse martensitic transformation, therefore only induced by heating a sample from the deformed martensite phase. In this study, we report a phenomenon of cooling-induced SME, observed in a Co2Cr(Ga,Si) Heusler alloy, where the normal heating-induced SME can be obtained at the same time. The cooling-induced SME is attributed to an abnormal martensitic transformation in Co2Cr(Ga,Si) Heusler alloy. Moreover, an inverse temperature dependence of superelastic stress was also observed. The discoveries of these phenomena provide application possibilities for shape memory alloys, especially at low temperatures. (C) 2013 AIP Publishing LLC.

In this report, we present findings of systematic research on NiCoMnAl alloys, with the purpose of acquiring a higher thermal transformation arrest temperature (T-A). By systematic research, T-A in the NiCoMnAl alloy systems was raised up to 190 K, compared to the highest T-A of 130 K in NiCoMnIn. For a selected alloy of Ni40Co10Mn33Al17, magnetization measurements were performed under a pulsed high magnetic field, and the critical magnetic field-temperature phase diagram was determined. The magnetic phase diagram for Ni50-xCoxMn50-yAly was also established. Moreover, from the discussion that the formerly called "kinetic arrest phenomenon" has both thermodynamic and kinetic factors, we suggest a terminology change to the "thermal transformation arrest phenomenon".

Magnetic field-induced transition of Ni45Co5Mn36.7In13.3 was investigated under magnetic fields with different sweeping rates. A static magnetic field produced by a superconducting magnet, a semi-static magnetic field created by a flywheel DC generator-powered magnet, and a pulsed magnetic field resulting from a condenser bank-powered magnet were used in this study, which covers sweeping rates of more than 6 orders. The magnetic field hysteresis is enlarged with increasing sweeping rate. The experimental results were consistent with a phenomenological model, and the activation energy for the thermally activated process was determined to be 0.7 eV for this alloy. (C) 2013 AIP Publishing LLC.

The magnetization distribution in Co2FeSi which has the largest moment per formula unit ∼6 μB of all Heusler alloys, has been determined using polarized neutron diffraction. The experimentally determined magnetization has been integrated over spheres centred on the three sites of the L12 structure giving μ Fe = 3.10(3) μB and μ Co = 1.43(2) μB, results which are slightly lower than the moments in atomic spheres of similar radii obtained in recent LDA + U band structure calculations (Li et al 2010 Chin. Phys. B 19 097102). Approximately 50% of the magnetic carriers at the Fe sites were found to be in orbitals with e g symmetry. This was higher, ≃65%, at the Co sites. Both Fe and Co were found to have orbital moments that are larger than those predicted. Comparison with similar results obtained for related alloys suggests that there must be a finite density of states in both spin bands at the Fermi energy indicating that Co2FeSi is not a perfect half-metallic ferromagnet. © 2013 IOP Publishing Ltd.

Permeability, magnetization and differential scanning calorimetry measurements are carried out on Pd2Mn1+xSn1-x (0 &lt;= x &lt;= 0.50). On the basis of the experimental results, the phase diagram in the temperature-concentration plane is determined. The determined phase diagram is spanned by a paramagnetic austenite phase (P-A), a paramagnetic martensite phase (P-M), a ferrimagnetic austenite phase (F-A) and a martensite phase (F-M) with a small spontaneous magnetization. It is found that Pd2Mn1+xSn1-x has the characteristics of the phase diagrams of Ni(2)Mn(1+x)Z(1-x) (Z = In, Sn) metamagnetic shape memory alloys. (C) 2012 Elsevier B. V. All rights reserved.

The magnetization measurements at 5 K were carried out for Ni2Mn1 - xCuxGa (0 &lt;= x &lt;= 0.40) and Ni2MnGa1 - yCuy (0 &lt;= y &lt;= 0.25) alloys. All of the magnetization curves are characteristic of ferromagnetism or ferrimagnetism. By using Arrott plot analysis the spontaneous magnetization of all samples was determined from the magnetization curves. The magnetic moment per formula unit, mu(s), at 5 K was estimated from the spontaneous magnetization. For Ni2Mn1 - xCuxGa (0 &lt;= x &lt;= 0.40) alloys mu(s) at 5 K decreases linearly with increasing x. On the other hand, the mu(s) at 5 K for Ni2MnGa1 - yCuy (0 &lt;= y &lt;= 0.25) alloys decreases more steeply with increasing x compared to the mu(s) for Ni2Mn1 - xCuxGa (0 &lt;= x &lt;= 0.40) alloys. On the basis of the experimental results, the site-occupation configurations of Ni2Mn1 - xCuxGa (0 &lt;= x &lt;= 0.40) and Ni2MnGa1 - yCuy (0 &lt;= y &lt;= 0.25) alloys are proposed.

A phenomenological theory is presented to study the multiferroic system in the shape memory alloys Ni2Mn1+xIn1-x with the Heusler-type structure, where the phase transitions are characterized by the two order parameters, i.e., the martensitic distortion e(3) and the magnetization M. The Landau free energy is expanded in powers of e(3) and M with including the Zeeman energy and the energy increase by the uniaxial force on e(3). The resultant free energy is applied to analyze the experimental results, such as the phase diagram in the temperature-concentration plane and the reentrant ferromagnetism by increasing temperature. The magnetic fields are shown to cause the ferromagnetic-ferromagnetic or metamagnetic transitions as observed. Further, it is predicted that the uniaxial force can dominate the appearance of the ferromagnetism in some alloys. It is found that these exotic behaviors of this alloy system are all ascribed to the repulsive interaction between e(3) and M, which originates from their biquadratic term. Through the present analyses, it is verified that this repulsive interaction is expected in other alloy systems Ni2Mn1+xX1-x (X = Sn, Sb) and makes a contrast to the attractive interaction realized in another group of the alloy systems including Ni2+xMn1-xGa and Ni2Mn1-xCuxGa. (c) 2012 Elsevier B.V. All rights reserved.

The temperature dependence of the resonance frequency of Co-59 NMR in a ferromagnetic Heusler alloy, Co2FeSi, in zero applied field is reported. The temperature dependence in the range 4.2-300 K has been found to be well described by nu - nu(0)(1 - BT3/2) with nu(0) - 139.1 MHz, and B - 5.32 x 10(-6) K-3/2, which corresponds to the spin-wave stiffness constant D of 2.60 m eV nm(2). The behavior is roughly in agreement with the temperature dependence of the macroscopic magnetization and is consistent with the dominance of the spin-wave excitations in Co2FeSi at low temperatures. (C) 2012 Elsevier B. V. All rights reserved.

Temperature dependence of the equilibrium transformation field (H 0) for Ni50Mn34.4In15.6 metamagnetic shape memory alloy was precisely determined by electrical resistivity measurements using a pulsed magnet. The H0-T curve was found to exhibit a maximum at around 50 K, suggesting that the transformation entropy change becomes negative in the lower temperature region. The residual electrical resistivity in the field-induced parent phase at lower temperatures was about 10 × 10-8 Ω·m, being normal value as the ferromagnetic alloys, whereas that in the martensite phase was high of about 200 × 10-8 Ω·m. The temperature dependence of the magnetic field hysteresis can be well fitted with the Seeger's theory proposed for plastic deformation by dislocations. © 2013 The Japan Institute of Metals.

In situ microscopic study was carried out on Ni44.3Co5.1Mn31.4Al19.2 metamagnetic shape memory alloy under a pulsed magnetic field up to 35.5 T. Magnetic field-induced reverse martensitic transformation was directly observed. The critical magnetic fields were determined from the contrast change of the microstructure, where good agreement had been found by magnetization measurement in a previous study. Comparison of the micrographs during thermal and magnetic field cycles between Ni45Co5Mn36.7In13.3 and Ni44.3Co5.1Mn31.4Al19.2 was conducted. It is concluded that though the energy barrier related to thermal activation strongly effects the martensitic transformation of Ni45Co5Mn36.7In13.3, its effect is very small on Ni44.3Co5.1Mn31.4Al19.2. Qualitative discussion yielded a reasonable understanding of the results of microstructure observation.

Electrical resistivity measurements in the temperature range from 6 to 300K were carried out in order to investigate the effects of the hydrogen absorption on the transport properties of Ni36Nb24Zr40 amorphous alloy ribbon. The electrical resistivity basically behaved negative temperature dependence in all prepared specimens of (Ni0.36Nb 0.24Zr0.40)100-xHx with 0 ≤ x &lt 15. The absolute value of temperature coefficient of the resistivity, TCR, increased with increasing the amount of the absorbed hydrogen. In addition, it was also clear that the electrical resistivity gradually increased with the time just after electrochemically charging, and tended to saturate after about 800 ks at 300 K. The behavior of the gradual increase in the electrical resistivity with the time was explained by the model including two kinds of the relaxation times, being associated with the migration of the hydrogen from the sample surface. © 2013 The Japan Institute of Metals and Materials.

Cooling rate and composition dependences of the magnetic susceptibility for Zr54-xCu30+xAl8Ag8 glassy alloys which are candidate materials for magnetic resonance imaging (MRI) were investigated. Lower magnetic susceptibility was achieved by reducing Zr content in the present series of the alloys, and also by higher cooling rate during the preparing glassy alloys. The magnetic susceptibility values were hard to be explained by the simple free-electron model. It is suggesting that the effects of the enhancement of the density of states by 4d-conduction band should be taken into the consideration. The results obtained by utilizing the pair correlation functions suggested that the different magnetic susceptibilities between the ribbon and bulk glassy alloys were originated from the structural difference in the middle range order caused by the different cooling rates. © 2013 The Japan Institute of Metals and Materials.

Permeability, magnetization, differential scanning calorimetry and X-ray powder diffraction measurements were carried out on the off-stoichiometric ferromagnetic shape memory alloys Ni50+xMn27-xGa 23 (-25 ≤ x ≤ 6) in order to establish the phase diagram over a wide range of concentration. The phase diagram was found to comprise of four regions, a paramagnetic austenite phase (Para-A), a paramagnetic martensite phase (Para-M), a ferromagnetic austenite phase (Ferro-A) and a ferromagnetic martensite phase (Ferro-M). Furthermore the martensitic transformation and the Curie temperatures crossed over at around x = 2.5. The martensitic transformation was found to occur over a wide Mn-rich region. A linear increase in the martensitic transformation temperature with increasing number of valence electrons per atom, e/a, was limited to a narrow concentration range around x = 0.0. Overall the martensitic transformation temperature exhibited a concave behavior with a minimum occurring at approximately x = -8. © 2013 Elsevier B.V. All rights reserved.

Neutron powder diffraction measurements were carried out in a wide temperature range from 14 to 500 K for Ni2Mn0.3Fe 0.7Ga alloy, which undergoes a martensitic transformation from L21-type austenite phase to four layered orthorhombic-type martensite phase at about 160 K during cooling. For the diffraction pattern measured at 500 K in the paramagnetic austenite phase, it was clarified that the Mn and Fe atoms randomly occupied 4a site in the L21-type structure. Magnetic moments of Ni, Mn and Fe in the ferromagnetic austenite phase at 200 K were decided to be 0.3 and 3.3 and 3.0 lB, respectively. The magnetic moment of Fe is significantly larger than that in pure bcc-Fe of 2.2 lB. Magnetic moments of Fe in two sites at 14 K in the martensite phase were obtained to be 2.3 and 2.6 lB, respectively, suggesting that the comparatively large magnetic moments of Fe were kept even in the martensite phase. Total magnetic moment of the martensite phase at 14 K from the neutron powder diffractive analyses is 3.7 μB/f.u., being in good agreement with the result of the magnetic measurement of 3.5 μB/f.u. at 4.2 K. © 2013 Elsevier B.V. All rights reserved.

Direct measurements of reversible magnetic-field-induced strain (MFIS) on a single crystalline Ni45Co5Mn36.5In13.5 metamagnetic shape memory alloy were attained via magnetic-field-induced martensitic transformation under different stress levels and at various temperatures. This was achieved using a custom-designed micro-magneto-thermo-mechanical testing system capable of applying constant stress while measuring strain and magnetization simultaneously on the samples, which can fit into conventional superconducting magnets. MFIS levels are reported as a function of temperature, magnetic field and external bias stress. It was necessary to apply an external bias stress in these materials to detect a notable MFIS because a magnetic field does not favor a specific martensite variant resulting in no shape change even though magnetic field leads to reversible martensitic transformation. Fully recoverable transformation strains up to 3.10% were detected under repeated field applications in the presence of different compressive stress levels up to 125 MPa. The bias stress opposes the field-induced martensite-to-austenite phase transformation and causes the critical field for the transformation to increase at a given temperature in accordance with the Clausius Clapeyron relationship. The effect of the bias stress on the kinetic arrest of austenite is also explored. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

A new magnetic shape memory alloy Pd2Mn1.46Sn0.54 has been synthesized. It was found that in the austenite phase Pd2Mn1.46Sn0.54 crystallizes in the L2(1) structure. It was confirmed from the low temperature X-ray diffraction measurements that the martensite phase of Pd2Mn1.46Sn0.56 has an orthorhombic four-layered structure. The magnetization versus temperature curve of Pd2Mn1.46Sn0.54 is very similar to those of the Ni-Mn-Z (Z = In, Sn and Sb) magnetic shape memory alloys; the paramagnetic-ferromagnetic transition appears in the austenite phase with decreasing temperature. With further decrease of temperature, the magnetization and permeability decrease abruptly at the martensitic transition temperature. The martensite phase remains ferromagnetic at low temperatures. (C) 2012 Elsevier B. V. All rights reserved.

Thermal and electrical transport properties, such as thermal diffusivity, the electrical resistivity and thermopower of the Zr-based bulk metallic glassy (BMG) alloys of Zr42Cu42Ag8Al8 and Zr55Al10Cu35-xNix (x = 0, 5 and 10) with high glass-forming ability were investigated. Thermal diffusivity is comparatively low at about 2 x 10(-6) m(2) s(-1), reflecting the aperiodic crystal structure of the BMG, whereas it becomes higher and depends on the alloy compositions after their crystallization. The phonon contribution to the thermal conductivity of the BMG alloys is thought to be small, based on a comparison with the estimated value of the electronic contribution to the thermal conductivity from the Wiedemann-Franz law. The thermopower of the present Zr-based BMG alloys shows a small positive Value around room temperature, which is a general feature of nonmagnetic amorphous alloys. [doi:10.2320/matertrans.M2012163]

The phase equilibria in the Mn-rich portion of Mn-Ga binary system were experimentally determined. The topological feature of the determined diagram was found to be similar to that reported by Wachtel and Nier [17] while the eta phase with the D0(19) structure exists in a wider temperature and composition range and the tau phase has a wider solubility range. The complicated composition dependence on magnetization of the Mn-rich alloys reported by Masumoto et al. can successfully be explained with the determined phase diagram. (C) 2012 Elsevier B.V. All rights reserved.

The crystal structures, spontaneous magnetic moment, I-s, and the Curie temperature, T-C, of Fe2CrAl and Fe2CrGa Heusler alloys were investigated. Single phases of A2, B2 and L2(1)-type structures were obtainable in Fe2CrAl alloy by controlling the annealing temperature. The values of the I-s and T-C of the A2-type phase were 2.2 mu(B)/f.u. and 316 K and those of the B2-type phase were 2.0 mu(B)/f.u. and 274 K, larger than those of the L2(1)-type phase of 1.6 mu(B)/f.u. and 210 K, respectively. A single phase of the A2-type phase in Fe2CrGa alloy was obtained and the I-s and T-C were about 2.8 mu(B)/f.u. and 353 K, respectively. The B2 or L2(1)-type single phases of Fe2CrGa alloy could not be obtained because of the inevitable precipitants. (C) 2012 Elsevier B.V. All rights reserved.

Permeability, magnetization, and differential scanning calorimetry measurements are carried out on the ferromagnetic shape memory alloys Ni 2MnGa 1-xCo x (0≤x≤ 0.20). On the basis of the experimental results, the phase diagram in the temperature-concentration plane is determined. The determined phase diagram is spanned by a paramagnetic austenite (Para-A) phase, paramagnetic martensite phase, ferromagnetic austenite phase, ferromagnetic martensite (Ferro-M) phase, and a premartensite phase. The measurements show that a magnetostructural transition between the Para-A and Ferro-M phases does not appear in this alloy system. The phase diagram is discussed using phenomenological Landau theory. © 2012 American Physical Society.

The concentration dependence of the order-disorder phase transformation temperature from the L2(1) to the B2 phase (T-t(L21/B2)) and magnetic properties of Co2Fe(Ga1-xSix) and Co2Fe(Al1-ySiy) Heusler alloys were investigated. In the phase diagrams, a crossover of the Curie temperature (T-C) and T-t(L21/B2) was confirmed at around y = 0.45 in Co2Fe(Al1-ySiy), whereas the T-C and T-t(L21/B2) monotonically changed with x in Co2Fe (Ga1-xSix). The slopes of the linear concentration dependence of T-t(L21/B2) for Co2Fe(Al1-ySiy) drastically changed at about y = 0.45, suggesting that the chemical interchange energy between Fe and Al in Co2FeAl alloy is affected by the magnetic ordering. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3700220]

Permeability, magnetization, and differential scanning calorimetry measurements are carried out on the ferromagnetic shape memory alloys Ni2MnGa1-xCox (0 &lt;= x &lt;= 0.20). On the basis of the experimental results, the phase diagram in the temperature-concentration plane is determined. The determined phase diagram is spanned by a paramagnetic austenite (Para-A) phase, paramagnetic martensite phase, ferromagnetic austenite phase, ferromagnetic martensite (Ferro-M) phase, and a premartensite phase. The measurements show that a magnetostructural transition between the Para-A and Ferro-M phases does not appear in this alloy system. The phase diagram is discussed using phenomenological Landau theory.

X-ray powder diffraction and magnetization measurements have been carried out on Rh2Mn1+xSn1-x (0 &lt;= x &lt;= 0.3) alloys. The alloys, which crystallize in the L2(1) structure, were found to exhibit ferromagnetic behavior. The lattice constant a at room temperature decreases with increasing x, whereas the Curie temperature T-C decreases linearly. At 5 K the magnetic moment per formula unit first increases with increasing x and then saturates for x &gt;= 0.2. The experimental results are discussed in terms of the influence of the Mn-Mn exchange interactions between the Mn atoms on the Sn and Mn sites. (C) 2011 Elsevier B.V. All rights reserved.

Magnetic properties and martensitic transformation response of the Ni43Co7Mn39Sn11 metamagnetic shape memory alloy compacts fabricated by pressureless sintering were investigated. The porous specimens sintered at 1173 K for 48h show drastic change of electrical resistivity and magnetization due to martensitic transformation, and the features of magnetic-field-induced martensitic transformation behavior are almost the same as those in bulk specimens. In the porous specimens, the large metamaenetic shape recovery ratio over 40% was observed at 320 K with the application of 8T magnetic field. [doi:10.2320/matertrans.M2011258]

This paper reports on the unexpectedly narrow magnetic domain walls observed at the positions of antiphase boundaries (APB) in a system of ferromagnetic shape memory alloys Ni50Mn25Al12.5Ga12.5. Lorentz microscopy observations determined the wall width at the APB position to be 12 nm, which is substantially smaller than the width at the APB-free position of 48 nm. This result can be explained by the modulation of magnetic parameters near APB, within which ferromagnetism is suppressed by the deterioration of Heusler-type ordering. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The spin-wave stiffness constant D and the Curie temperature for series of L2(1) phase in Co2CrGa, Co2MnGa, Co2Mn(Al1-xSix), Co2Fe(Al1-xSix), and Heusler alloys were evaluated from the thermomagnetization measurements. For the Co2CrGa, Co2MnGa, and Co2Mn(Al1-xSix) alloys, there was a linear relation between D and T-C. The tendency between D and T-C was different from that for Co2Mn(Al1-xSix) and Co2Fe(Ga1-xSix) alloys, that is, T-C was in the temperature region from 1040 to 1100 K indicating weak concentration dependence, whereas D was sensitive to the composition. For example, D changed from 2.28 meV . nm(2) for x = 1 (Co2FeSi) to 5.24 meV . nm(2) for x = 0 (Co2FeGa) in the case of Co2Fe(Ga1-xSix) alloys. It was suggested that magnetic stability against the temperature of the Co-based Heusler alloys containing Fe element was governed not only by the spin-wave excitation but also by the other kinds of excitation.

Magnetic measurements in Ni50Mn50x-In-x alloys were performed in order to investigate the effect of the degree of order on the magnetic properties for specimens annealed at different temperatures. It was confirmed that Curie temperature, T-C, and spontaneous magnetization, mu(m), in as-quenched specimens with a low degree of order exhibited composition dependence of indium basically similar to those in as-annealed ones with a high degree of order reported in a previous paper. However, especially in the In-rich region of x &gt; 25, both the T-C and the mu(m) obtained from the as-quenched specimens were lower than those from the as-annealed specimens. [doi:10.2320/matertrans.M2011125]

DC and AC magnetic measurements were carried out to clarify the difference in the magnetic ground state depending on the kinds of Z element used in the martensite phase in Ni-Mn-Z (Z = In, Sn and Sb) off-stoichiometric Heusler alloys. Magnetic field cooling effects were observed in the DC thermomagnetization curves in the low temperature regions, and a frequency dependence on AC susceptibility was also observed in both real and imaginary parts of the susceptibility. Negative divergence was clearly observed in nonlinear AC susceptibility only for the Ni50Mn40Sb10 alloy, suggesting that the magnetic feature of its ground state is the spin-glass state. The magnetic ground state of the martensite phase in these alloys would relate to the magnetic configuration of the Mn atoms in the ferromagnetic austenite phase.

The effects of anti-phase domain (APD) boundaries on the magnetic properties of Ni2Mn(Ga0.5Al0.5) alloy were studied by magnetic measurements and transmission electron microscopic observations. The growth of APDs at 773 K followed the square root law for annealing time. While the saturation magnetization and the Curie temperature were hardly affected by the APD size, the magnetization curve in the specimen with smaller mean APD size became harder, caused by the pinning effect of the magnetic domain walls due to the APD boundaries. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Magnetic properties of the B2 phase in Co50-xNixMn25Al25 alloys were investigated. Spontaneous magnetization M-s measured at 4.2 K increases linearly with increasing x in the region of x &lt;= 30 in accordance with following the generalized Slater-Pauling (GSP) line. However, Ms abruptly decreases with increasing x and deviates from the GSP line in the Ni-rich region of x &gt; 30, suggesting a drastic change in the density of states at the Fermi energy. The Curie temperature T-C decreases monotonically with increasing x and significantly decreases in the region of x &gt; 30. Antiferromagnetic evidence is clearly observed at x &gt; 45, and the Neel temperature TN increases with increasing x, in reaching the value of the B2 phase in Ni2MnAl. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3559536]

Magnetocrystalline anisotropy of the martensite phase was investigated in a single crystal of Fe(44)Mn(28)Ga(28) shape memory alloy. It was found that the martensite phase of Fe(44)Mn(28)Ga(28) alloy has a tetragonal distorted L2(1) structure, with a = 0.5368 nm and c = 0.7081 nm. An approximately single variant was obtained by thermomechanical treatment, and magnetization measurement revealed that the c-axis is the magnetic easy axis. The magnetocrystalline anisotropy constant K(u) was determined to be 7.6 x 10(5) J m(-3) at 300 K. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The concentration dependence of magnetic properties in the austenite phase of Ni50Mn50-xInx/2 Sb-x/2 Heusler alloys was systematically investigated by magnetization measurements. The Curie temperature for Ni50Mn50-xInx/2Sbx/2 alloys is almost independent of content x. On the other hand, the concentration dependence on magnetic moment shows a concave curve similar to that of Ni50Mn50-xSnx alloys, which have the same number of valence electrons. This tendency suggests that the magnetic moment continues to increase with decreasing content x and reaches that of the metastable ferromagnetic NiMn-B2 phase. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3556708]

High-field magnetic measurements were carried out in order to investigate behaviors of field-induced reverse martensitic transformation and kinetic arrest of NiCoMnSn metamagnetic shape memory alloy. In the thermomagnetization curves, it was confirmed that the reverse martensitic transformation temperature decreases 67 K by applying magnetic field of 5T, while in the magnetic field cooling process under 5T, martensitic transformation does not occur down to low temperatures. Equilibrium magnetic field, defined from the critical magnetic fields of the metamagnetic evidence in the magnetization curves, exhibits almost constant below about 100 K, suggesting that the entropy change becomes zero, which is considered to cause kinetic arrest behavior. (C) 2010 Elsevier B.V. All rights reserved.

In this chapter, the order-disorder phase transformation from the B2 to the L21-type phase and magnetic properties of Ni2Mn(GaxAl1-x) and Ni2Mn1+yIn1-y alloys are introduced, and the influence of martensitic transformation on the magnetic properties in NiMnIn-based alloy is also discussed. The magnetic properties of these alloys are significantly sensitive to the degree of long-range order, the alloy composition, and the crystal structure, and themagnetism varies among paramagnetic, ferromagnetic, and antiferromagnetic properties, in dependence on these factors. On the whole, the magnetic properties are mainly governed by the magnetic moments of Mn atoms and can be understood by taking into account the sign and the strength of the magnetic exchange interactions in Mn-Mn and Ni-Mn pairs. © Springer-Verlag Berlin Heidelberg 2012.

Magnetic measurements and neutron powder diffraction experiments on Ni50Mn33Sn17 and Ni45Co5Mn33Sn17 alloys were performed in order to establish the magnetic structures and the effects of Co substitution on the magnetic properties. It was shown that the magnetic coupling between the Mn moments on the 4a and 4b sites changed from being antiferromagnetic to ferromagnetic by substitution of Co. As a result of the change in the magnetic structure due to the Co substitution, the ferromagnetic properties of Ni-Co-Mn-Sn are enhanced. These results have enabled the concentration dependence of the magnetic moment to be quantified. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3548558]

Mechanical and shape memory properties of Ni43Co7Mn39Sn11 metamagnetic shape memory sintering compacts, fabricated by pressureless sintering, were investigated. With sintering time the porosity drastically decreases and the ductility is significantly enhanced compared to the samples obtained by conventional induction melting. Moreover, the fracture strain in the specimen sintered at 1173 K for 144 h is almost the same as that in the high density sintering compacts by spark plasma sintering. Interestingly, the shape memory effect decreases with decreasing porosity. (c) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The concentration dependence of magnetic properties in the austenite phase of NiCoMnIn and NiCoMnSn Heusler alloys was systematically investigated by the magnetization measurements. The T(C) for Ni((50-x))CoxMn((50-y))Sn(y) alloys linearly increases with increasing the Co content and fixed Sn content. Although showing a concave curve for Ni(50)Mn((50-y))Sn(y) ternary alloys, the Sn content-dependence of magnetic moment per formula unit changes from the concave curve to a straight line when Co is substituted for Ni. On the other hand, the In content-dependence of the magnetic moment for Ni(45)Co(5)Mn((50-y))In(y) alloys is perfectly linear as is that in the Ni(50)Mn((50-y))In(y) ternary alloys. (C) 2010 American Institute of Physics. [doi:10.1063/1.3525168]

Magnetization measurements have been carried out at high pressure up to 12.1 kbar for Co2VAl and Co2VGa with a miniature high-pressure clamp cell. The magnetic moment measured at 5 K is independent of pressure for Co2VGa. This is an experimental observation that gives clear evidence that Co2VGa possesses half-metallic electronic structure. On the other hand, a sizable pressure dependence of the magnetic moment is observed for Co2VAl and it is attributed to the precipitation of the bcc particles in the matrix L2(1) phase. The Curie temperature decreases with increasing pressure for Co2VGa, reflecting characteristics typical for usual itinerant electron systems. The negative pressure dependence of the Curie temperature found in Co2VGa contrasts fairly with that of other Heusler alloys containing Mn atoms.

The structural properties of metamagnetic shape memory alloy Ni40Co10Mn34Al16 were investigated by X ray powder diffraction measurements in the temperature range from 283 to 473 K and magnetic fields up to 5 T With increasing temperature from 283 K the alloy undergoes the reverse martensitic transformation from the tetragonal L1(0) type structure with the lattice parameter a(t) = 0 3853 nm and c(t) = 0 3299 nm into the B2 type cubic structure with the lattice parameter a(c) = 0 2924 nm at A(s) = 383 K At 408 K (&gt;A(s)) we directly observed the field induced reverse martensitic transformation [doi 10 2320/matertrans M2010150]

Pd2Mn1+xSn1-x(0 &lt;= x &lt;= 0.30) alloys crystallize in the cubic L2(1) structure. The lattice parameter a decreases linearly with increasing Mn concentration x. X-ray powder diffraction patterns indicate that the excess Mn atoms occupy the vacant Sn sites. All alloys exhibit the ferromagnetic behavior. The pressure change of the magnetic moment per formula unit at 5 K for Pd2MnSn is independent of pressure. The Curie temperature of Pd2Mn1+xSn1-x(0 &lt;= x &lt;= 0.30) alloys increases linearly with increasing x. Magnetization measurements make clear that the magnetic moment of Mn atoms, which substitute for Sn sites, is coupled antiferromagnetically to the magnetic moment of Mn atoms on the ferromagnetic Mn sublattice. (C) 2010 Elsevier B.V. All rights reserved.

Heat-induced and isothermal martensitic transformations from kinetically arrested parent phase in Ni(45)Co(5)Mn(36.7)In(13.3) metamagnetic shape memory alloy were investigated by magnetization measurements. A drastic drop of magnetization due to martensitic transformation during heating was observed. The isothermal martensitic transformation was confirmed to appear for sonic combinations of temperature and field. Incubation time for the transformation strongly depended on the holding condition, and the specimen held in conditions near the martensitic start (M(s)) line determined by magnetization measurements showed a shorter incubation time. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Magnetic properties and martensitic transformation behaviors of NiCoMnAl metamagnetic shape memory alloys were investigated. The kinetic arrest phenomenon was observed at about 40 K during thermomagnetization measurements. At temperatures ranging from 4.2 to 200 K, magnetic field-induced reverse transformation was confirmed by a pulse magnetometer with a magnetic field up to 45 T. By plotting the equilibrium magnetic fields against the measured temperature, the transformation entropy change was calculated by using the Clausius-Clapeyron equation. The transformation entropy change was found to become zero below 40 K, which can explain the appearance of the kinetic arrest phenomenon. [doi: 10.2320/matertrans.M2010098]

Site occupancies of Co, Y(Y=Ti, V, Cr, Mn and Fe) and Ga atoms for the L2(1) phase in Co2YGa alloys annealed at 773 K were precisely investigated by powder neutron diffraction measurement. While Co atoms in all the five alloys almost perfectly occupy the x (2a) site, the occupancy of the z(4b) site by Ga atoms depends on the kind of Y atom, and it decreases with increasing number of valence electrons except for Co2CrGa alloy. Degrees of long-range order on the z site occupancy of Ga atoms experimentally determined for all the alloys are in good agreement with those thermodynamically estimated from their order-disorder transition temperatures using the Bragg-Williams-Gorsky approximation. (C) 2010 Elsevier B.V. All rights reserved.

Shape memory response of the polycrystalline Ni40Co10Mn33Al17 alloy were investigated. In the isobaric thermal cycling experiments, the measured transformation strain levels increased with increasing stress reaching about 3.6% under 200 MPa. The slope of he stress vs. transformation temperature diagram, constructed using the data from these experiments, almost coincided with the predicted one obtained using the Clausius-Clapeyron equation, and experimental entropy data and transformation strain. Perfect pseudoelasticity was observed up to 405 K during compressive straining up to 2.5%. [doi: 10.2320/matertrans.MBW200903]

Spin and orbital magnetic moments of the L2(1)-type Co2FeGa Heusler alloy have been investigated using x-ray magnetic circular dichroism spectra in the soft x-ray region. From the spectra of the L-2,L-3-edge of Co and Fe, the ratios of the orbital magnetic moment to the spin magnetic moment M-orb/M-spin are estimated to be 0.06 for Co and 0.02 for Fe, in agreement with the available theoretical values. The orbital magnetic moments of these two elements are small in line with theoretical results, reflecting the high symmetry of the L2(1)-type crystal structure. Furthermore, it has been confirmed that the magnetic moment of Ga is induced in the present alloy.

Martensitic and magnetic properties of Ni33.0Co13.4Mn39.7Ga13.9 metamagnetic shape memory alloy were investigated. The kinetic arrest phenomenon was observed at about 120 K by thermomagnetization measurements, and magnetic field-induced transformation (MFIT) was also detected at various temperatures ranging from 4.2 to 300 K. By evaluation of the equilibrium magnetic fields and temperatures based on the transformation fields and temperatures, it was confirmed that the transformation entropy change below 120 K becomes almost zero, which results in the kinetic arrest phenomenon. [doi: 10.2320/matertrans.MBW200915]

The order-disorder transformation and the magnetic properties of Heusler-type Ni50Mn50-xInx ternary alloys were investigated. The B2/L2(1) order-disorder transformation temperatures are detected at about 800-1100 K. In the alloys with the L2(1) structure, while the spontaneous magnetization at 4.2 K monotonically decreases with increasing x, the Curie temperature is almost constant with x &lt;= 25 and decreases linearly with x &gt; 25. This unique behavior is qualitatively explained by the concept of local magnetic moment of Mn atoms. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The electronic specific heat coefficient gamma, and the high field susceptibility chi(hf) of the L2(1) phase in Co-based Heusler alloys were investigated in order to relate these properties to the spin polarization P. The gamma-values of Co(2)CrGa, Co(2)MnGa and Co(2)FeGa alloys are comparable to the theoretical values of the total density of states at the Fermi energy. The value of chi(hf) for Co(2)CrGa alloy having a high spin polarization of about 95% is significantly low on the order of 10(-4) mu(B)/f.u.-T. In contrast, chi(hf) for Co(2)FeGa alloy having a theoretical P value of 37% is one order larger than that for Co(2)CrGa alloy. These results imply that there is a relation between chi(hf) and P of the present Co-based Heusler alloys.

Magnetic properties and phase stability of the L2(1) phase in Co-2(Ti1-xMnx)Ga alloys were investigated by magnetic and DSC measurements. The order-disorder phase transition temperature from the L2(1) to the B2 phase T-t(L21/B2) was found to increase linearly with increasing Ti composition and its linear extrapolation to x = 0.0 accords with the reported value of T-t(L21/B2) for the Co2TiGa alloy. The Curie temperature T-C increases with increasing Mn composition, exhibiting an upward convexity, but is rather independent of composition in the high Mn region. It is concluded that the Co-2(Ti1-xMnx)Ga alloys located in the middle composition range possess both a high T-C and a high T-t(L21/B2).

Magnetization and initial permeability measurements were done on the Heusler alloys Ni2-xCoxMnGa (0 &lt; x &lt; 2). On the basis of the results, the magnetic-phase diagram was determined for Ni2-xCoxMnGa (0 &lt; x &lt; 2). The Curie temperature T-C increases with increasing the Co concentration x. The martensitic transition temperature decreases abruptly with increasing x. The magnetic moment per formula unit at 5 K makes a broad maximum around x=1.0. The concentration dependence of the magnetic moment for Ni2-xCoxMnGa (0 &lt; x &lt; 2) has been calculated using the Korringa-Kohn-Rostoker method. The computational results of the magnetic moment are in good agreement with the experimental results in this study.

Stress-induced martensitic transformation below room temperature for a Ni45Co5Mn36.1In13.9 single-crystal, in which no martensitic transformation occurs during cooling down to 4.2 K under zero stress, was investigated by using compression test. The equilibrium stress estimated from the critical stresses in stress-induced forward and reverse transformations decreased with decreasing temperature, while it became almost constant at temperatures below about 140 K. This anomaly can be explained by the abnormal temperature dependence of the transformation entropy change, which has also been detected by magnetization measurement.

Magnetization and initial permeability measurements were done on the magnetic shape memory alloys Ni(2)Mn(1.48-x)Fe(x)Sn(0.52) (0 &lt;= x &lt;= 0.20). The Curie temperature T(C) in the austenite phase increases slightly with increasing x. Similarly, the Curie temperature T(C)&apos; in the martensite phase increases with increasing x. The martensitic transition starting temperature M(s) decreases steeply with increasing x. The paramagnetic state of the martensite phase collapses in the Fe-rich alloys. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

We investigated the magnetoresistance effect for a magnetic tunnel junction (MTJ) using a Co2Ti0.5Mn0.5Al electrode on a Cr buffered MgO(001) single crystal substrate. The Co2Ti0.5Mn0.5Al formed an ordered L2(1) and B2 structures after post-annealing above 873 K and below 773 K, respectively. Maximum magnetization and minimum coercivity were exhibited in Co2Ti0.5Mn0.5Al annealed at 673 K. The MTJ using a Co2Ti0.5Mn0.5Al electrode with B2 structure exhibited tunnel magnetoresistance (TMR) ratio of 37% at room temperature and 60% at 5 K. The TMR ratio was larger than that of MTJ using a Co2Ti0.5Mn0.5Al electrode with L2(1) structure in this study.

Martensitic transformation and magnetic properties were investigated for Ni43Co7Mn39Sn11 polycrystalline specimens obtained using the spark plasma sintering method. The microstructure of the specimen sintered at 1173 K for 15 min showed only a small number of pores, and the specimen's ductility was significantly higher than that of alloys fabricated by conventional induction melting. The martensitic and magnetic properties of the sintered specimen were basically similar to those of conventional bulk alloys. The metamagnctic shape memory effect, i.e. magnetic field-induced shape recovery, was confirmed by the magnetic field of 8 T. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Martensitic and magnetic properties of Fe-Mn-Ga single and polycrystalline alloys were investigated. It was found that Fe-Mn-Ga alloys exhibit martensitic transformation from the paramagnetic L2(1) Heusler parent phase to the ferromagnetic L1(0) martensite phase. The martensitic transformation temperatures increased by about 20 K by the application of a magnetic field of 7 T, and a metamagnetic phase transition was observed. In addition, a magnetic field-induced strain of 0.6% associated with magnetic field-induced forward transformation was confirmed in an Fe(43)Mn(28)Ga(29) single crystal.

Magnetization measurements up to high magnetic fields of 56 T applied with a pulsed magnet were carried out for x = 14.0 and 15.6 in Ni50Mn50-xInx alloys. Metamagnetic behaviour from the nonmagnetic martensite phase to the ferromagnetic parent phase was observed even at x = 14.0, where no ferromagnetic phase exists in the entire temperature range under a low magnetic field. The spontaneous magnetization I-s for x = 14.0 and 15.6 was deduced to be about 6.4 and 6.0 mu(B)/f.u., respectively, and the I-s increased with decreasing In concentration. This result strongly suggests that the magnetic moment of Mn atoms substituted at the In sites couples ferromagnetically to the magnetic moment of Mn atoms at the Mn sites.

Magnetic change due to the martensitic transformation induced by high magnetic fields up to 18 T was investigated in the Ni50Mn34In16 metamagnetic shape memory alloy. Kinetic arrest of the martensitic transformation was observed and the martensitic transformation no longer proceeded at temperatures below around 100 K. The transformation entropy change between the martensite phase and parent phase evaluated from the magnetization curves showed an unusual behavior, changing from positive to negative at about 80 K. © 2008 Acta Materialia Inc.

The effects of chemical order on the phase stability and magnetic properties of the metamagnetic shape memory alloy Ni45Co5Mn36.7In13.3 were investigated. Alloys quenched from the B2 and L2(1) phase regions were found to transform to the L1(0) and 6M martensite phases, respectively. For alloys quenched from the B2 region the martensitic transformation starting temperature is about 80 K higher than that for alloys quenched from the L2(1) region. The Curie temperature of the parent phase and the magnetization of the martensite phase were both lower for the alloy quenched from the B2 region than those for the alloy quenched from L2(1) region.

The phase stability and magnetic properties of Ni2Mn(GaxAl1-x) alloys were studied by differential scanning calorimetric and magnetometric measurements, and X-ray diffraction and transmission electronic microscopic observations. The order-disorder transition temperature from the B2 to the L2(1) phase, T-t(B2/L21), linearly increases with increasing x and the magnetic properties depend on the annealing conditions. Especially in the Ni2Mn(Ga0.5Al0.5) alloy, the condition of the atomic order can be varied from a B2 to an L2(1) structure by the annealing temperature. The magnetic property of the fully ordered L2(1) phase is ferromagnetic with a Curie temperature T-C of about 380 K, while that in the B2 phase is antiferromagnetic with the Neel temperature T-N of about 300 K. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The order-disorder phase transition temperature from L2(1) to B2 phase T-t(L21/B2) the saturation magnetization M-s and the Curie temperature T-C were investigated in Co-2(Ti1-xFex)Ga. It was confirmed that T-t(L21/B2) for 0.8 &lt;= x &lt;= 1.0 almost linearly decreases with increasing x, and M-s follows the generalized Slater-Pauling line in the middle region of x. T-C also increases with increasing x, exhibiting an upward convexity. It is concluded that a relatively high T-t(L21/B2), a high T-C and a low M-s can be obtained in the present alloys. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Effects of the addition of Co to the NiMnAl alloy on the martensitic and magnetic properties were investigated. The magnetic properties of the parent (P) phase drastically changed from paramagnetic to ferromagnetic, while the magnetization in the martensite (M) phase slightly decreased with increasing Co composition. Consequently, in the Ni(40)Co(10)Mn(33)Al(17) alloy with the B2 ordered structure, the martensitic transformation from a ferromagnetic P to a weak magnetic M phase was obtained. The martensitic transformation temperatures in this alloy decreased by about 30 K with the application of a magnetic field of 7 T and a metamagnetic phase transformation was confirmed. (c) 2008 American Institute of Physics.

Martensitic and magnetic properties of NiCoMnSn metamagnetic shape memory alloy powders obtained by a gas atomization method were investigated. The as-atomized powders showed a dendritic structure which changed to a single-phase one by annealing at 1173 K for 2h. Although the martensitic transformation behavior was almost the same as that in bulk samples, the transformation thermal interval, namely, M-s - M-f, of the as-annealed powders decreased with increasing annealing time. In the powders annealed at 1173 K for 144h, a reversible metamagnetic phase transition was confirmed by the application of a magnetic field of 7T.

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The phase stability and magnetic properties of the L2(1) phase in CO2 Mn(Al1-xSix) Heusler alloys were investigated. The order-disorder phase transition temperature, T-t(L21/B2), increases linearly with increasing x; T-t(L21/B2) for CO2MnSi is estimated to be about 1580 K. These results mean that the stability of L2(1) phase of CO2MnSi is much higher than that of CO2MnAl. Although the saturation magnetic moment increases linearly with increasing x, i.e., consistent with the generalized Slater-Pauling behavior, the Curie temperature increases, exhibiting slightly upward convexity. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Magnetic properties and stability of L2(1) and B2 phases in the Co2MnAl Heusler alloy were investigated. It was confirmed that the order-disorder transition from the B2 to L2(1) phase is located at about 950 K and that the Curie temperature T-C of the L2(1) phase is 726 K which is about 50 K higher than that (T-C=677 K) of the B2 phase. The difference in T-C between the L2(1) and B2 phases is smaller than a theoretical prediction. On the other hand, the saturation magnetic moments M-s at 4.2 K for the L2(1) and B2 phases were estimated to be 4.07 mu(B)/f.u. and 4.16 mu(B)/f.u., respectively, comparable to the value M-t=4 expected from the generalized Slater-Pauling relation. (C) 2008 American Institute of Physics.

Magnetic properties, phase stability, electronic structure, and spin polarization ratio of L2(1)-type phase in Co-2(V1-xMnx)Ga Heusler alloys have been investigated experimentally and theoretically. The experimental magnetic moments M-s at 4.2 K linearly increase with increasing x, in situ with the generalized Slater-Pauling rule. The experimental Curie temperature T-C(expt.) exhibits a maximum value of about 704 K at x=0.75. The latter behavior is comparable to the calculated Curie temperature T-C(calc). from the theoretical effective exchange constant J(0). Although the order-disorder transition temperature T-t(L21/B2) from the L2(1)- to B2-type phase linearly decreases with increasing x, it is relatively high enough in the entire concentration region. The high value of T-t(L21/B2) means that the L2(1)-type phase can exist stably, which is very important for practical uses. The calculated density of states by the linear-muffitin orbital method with the atomic sphere approximation disclosed that the spin polarization ratio P of the alloy with x=0.75 is the highest in the present substituted alloys.

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Magnetic and electrical resistivity changes due to a martensitic transformation in large magnetic fields were investigated in a NiCoMnIn alloy. The transformation is interrupted at about 150 K during field cooling and does not proceed with further cooling. The obtained two-phase condition is frozen at low temperatures and zero field heating releases this condition, inducing a "forward" transformation. These unusual phenomena can be explained by an abnormal behavior in the transformation entropy change and an extremely low mobility of the phase interfaces detected at low temperatures. (c) 2008 American Institute of Physics.

The magnetic anisotropy of the La(0.75)Sm(0.25)Mn(2)Si(2) compound, which has a layered ThCr(2)Si(2)-type crystal structure, has been studied using a quasi-single-crystalline sample. It was found that the compound possesses a strong uniaxial magnetic anisotropy in both magnetically ordered and paramagnetic states. The magnetic anisotropy of the compound is mainly due to the Mn sublattice anisotropy. In the ferromagnetic state at 180 K, the magnetization process is characterized by the magnetic anisotropy constant K(1) = 6 x 10(6) erg cm(-3). In the paramagnetic state, a considerable anisotropy of paramagnetic Curie temperature Delta theta(p) approximate to 35 K and an appreciable difference between values of the effective magnetic moment measured along the c-axis and in the basal plane, Delta mu(eff) approximate to 0.4 mu(B) per formula unit, has been observed. The natural layered structure of the compound and partial unquenching of the Mn orbital momentum have been considered as possible reasons for the observed strong magnetic anisotropy.

We present magnetic properties, electronic structures and phase stability of L1(0)- and B2-type MnRh equiatomic alloys. The calculated density of states for the L1(0)-type equiatomic alloy in the collinear antiferromagnetic state exhibits a marked dip around the Fermi energy E-F. The experimental electronic specific heat coefficient gamma(e) of the L1(0)-type equiatomic alloy is comparatively low of about 5.0 mJ mol(-1) K-2, verifying the theoretical calculation. The effective exchange constant J(0) in the collinear antiferromagnetic state is given to be about 171.9 meV, corresponding to T-N = 1330K in the molecular field approximation scheme. The theoretical results predict that the antiferromagnetism of the B2-type equiatomic alloy is unstable, implying that the ground state is very weak ferromagnetic or non-magnetic. On the other hand, the total energy of the B2-type alloy in the paramagnetic state is lower than that of the L1(0)-type alloy, being consistent with the experimental fact that a diffusionless transformation between the L1(0)- and B2-type structures occurs below room temperature.

Martensitic, magnetic transformations, and crystal structures in Pd-In-Fe alloys were investigated. It was confirmed that some Pd-In-Fe alloys show martensitic transformation from a Heusler-type (L2(1)) ordered bcc phase to a 2M-type (DO22) structure and that an almost perfect superelastic effect accompany the transformation can be obtained. Furthermore, some alloys show transformation from the paramagnetic parent phase to the ferromagnetic martensite phase. (c) 2007 American Institute of Physics.

The B2/L2(1) order-disorder and magnetic transitions in Co2YGa (Y = Ti, V, Cr, Mn, Fe) alloys were investigated by electron probe microanalysis (EPMA), differential scanning calorimetry (DSC) and vibrating sample magnetometry (VSM). It was confirmed that the B2/L2(1) order-disorder transition temperature for the Co2YGa (Y = Ti, V, Cr) alloys monotonically decreases with increasing electron concentration of the Y site, whereas that of the Co2YGa (Y = Mn, Fe) alloys is almost constant at 1100 +/- 100 K. On the other hand, the Curie temperature T-C of all the alloys rises almost monotonically with increasing electron concentration of the Y site. (c) 2006 Elsevier B.V. All rights reserved.

The authors performed an optical spectroscopy to observe the electronic structure of L1(0)-type ordered Mn-based alloys. The effect of disorder on pseudogap formation in Mn1-xPtx (x=0.47, 0.50, 0.51, and 0.54) and Mn1-xPdx (x=0.502, 0.515, and 0.535) alloys has been clarified. The optical reflectivity shows a clear dip around 0.5 eV for both MnPt and MnPd alloys, which corresponds to the pseudogap formation. On the other hand, the pseudogap is rather unclear in the other nonequiatomic compositions. This indicates that the pseudogap formation is deeply related to the degree of the ordering in the Mn-based alloys. (c) 2007 American Institute of Physics.

The electrical resistivity, magnetic and low-temperature specific heat measurements, and theoretical calculations for L1(0)-type MnPd alloy system were carried out in a wide range of composition from 40 to 60% Pd. In the present antiferromagnetic alloy system, the highest Neel temperature T-N was observed in the vicinity of 53% Pd concentration, deviating from the equiatomic concentration. This behavior was also conformed by the theoretical calculations for the effective exchange constant J(0) which gives the value of TN. In the temperature dependence of electrical resistivity for the L1(0)-type MnPd alloys, a characteristic behavior of a hump just below TN was observed, which is associated with the pseudo-gap-type antiferromagnets. In addition, the value of the electronic specific heat coefficient ye is significantly small below 1 mJ mol(-1) K-2 above 50% Pd, reflecting the very low density of states at the Fermi energy E-F. The linear relation between the magnetic moment and the Pauling valence has been confirmed in the L1(0)-type Mn alloy systems, together with that of other Mn alloy systems. The present several results strongly imply that the characteristic electronic structure with the pseudo-gap and the Pauling valence (PV) associated with the covalent bonding state is closely interrelated in the L1(0)-type Mn alloy systems.

The theoretical calculations of magnetic anisotropy energy (MAE) for antiferromagnetic L1(0)-type MnTM [transition metal (TM)=Ni, Pd, Pt, Rh, and Ir] alloys were carried out on the basis of the local spin-density approximation using linear muffin-tin orbital method with atomic sphere approximation including the spin-orbit interaction. It has been demonstrated that the magnitude of the MAE for L1(0)-type MnIr alloy is highest, -20.77x10(6) J/m(3), and the negative sign of the MAE is consistent with the reported spin structure. On the other hand, the sign of the MAE for L1(0)-type MnPt alloy is positive in accordance with the spin structure. The MAE of the MnPt alloy is sensitive to the electron number, which would be correlated with the fact that only the MnPt alloy system exhibits a complicated magnetic phase diagram. (c) 2006 American Institute of Physics.

The electrical resistivity rho, magnetic susceptibility chi, electronic specific heat coefficient gamma(e), the Neel temperature T-N and the electronic structure and the magnetocrystalline anisotropy energy (MAE) have been investigated for L1(0)-type MnPt alloy system. This alloy system exhibits the characteristic behaviors of pseudo-gap type antiferrmagnets, presenting with the highest T-N, the smallest values of rho, chi and gamma(e), in the vicinity of the equiatomic composition. The values of rho, chi and gamma(e) increase with deviating from the equiatomic composition. From the linear muffin-tin orbital (LMTO) band calculations, the L1(0)-type MnPt alloy system has a pseudo-gap in the electronic structure and the density of suites (DOS) at the Fermi energy (E-F) is lowest at the equiatomic composition in accord with the experimental results. Furthermore. the results of the LMTO band calculations including the spin-orbit interaction make it clear that the direction of the magnetic moment of Mn in the equiatomic composition is parallel to the c-axis, consistent with the reported spin structure determined by neutron diffractions. The magnetocrystalline anisotropy constant K is about 1.39 x 10(6) J m(-3) which is larger in magnitude than that of L1(0)-type MnNi equiatomic alloy, though the signs are different.

Magnetic and half-metallic properties of Co-2(Cr1-xFex)Ga Heusler alloys have been investigated. In the entire concentration range, the L2(1)-type ordered phase is obtained. The saturation magnetic moment M-s at 4.2 K for x=0.0 (equivalent to Co2CrGa) is 3.01 mu(B)/f.u., in agreement with the generalized Slater-Pauling line and consistent with the theoretical value. The experimental value of M-s increases with increasing x, slightly larger than that of the theoretical value above x=0.60. The Curie temperature T-C also increases with x, and qualitatively accords with the theoretical values estimated from the effective exchange constant J(0). The present theoretical results disclose that not only the L2(1)-type ordered phase but also the B2-type phase exhibits high values of the spin polarization ratio P in a low concentration range of x. The ratio P of the L2(1)- and B2-type phases decreases with increasing x, because the large peak of the density of states at the Fermi energy for Cr in the majority spin band becomes smaller and a strong hybridization between Co-3d and Fe-3d makes a gap narrower in the minority spin band.

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The magnetic properties and phase stability of half-metal-type Co2Cr1-xFexGa alloys were investigated by differential scanning calorimetry (DSC), in a superconducting quantum interference device (SQUID) magnetometer and in a vibrating sample magnetometer (VSM), and by transmission electron microscopy (TEM). It was found that the L2(1)-type single-phase is obtainable for the entire concentration of x and that the value of the saturation magnetic moment M., at 4.2 K in the lower composition range of x is in agreement with the generalized Slater-Pauling line, while it is rather larger than the generalized Slater-Pauling line above x = 0.6. The Curie temperature T-c monotonically increases, whereas the transition temperature from the L2(1)- to B2-type phase T-1(B2/L21) is almost constant at 1082 +/- 13 K with increasing x. (c) 2005 Elsevier B.V. All rights reserved.

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The phase stability and magnetic properties of the half-metal-type Co2Cr1-xFexAl alloy system were investigated. It was found that the occurrence of two-phase separation is unavoidable in a concentration range of less than x=0.4, leading to deviation of the saturation magnetic moments from the generalized Slater-Pauling line. The L2(1)-type phase becomes stable in a concentration range of more than x=0.7, where no half-metallic behaviors are present. Consequently, it is concluded that the most favorable concentration for applications to spintronic devices is located around x=0.4 in Co2Cr1-xFexAl alloys having the B2-type phase. (C) 2004 American Institute of Physics.

The saturation magnetic moment M-s and the Curie temperature T-C of the half-metal-type Co2CrGa Heusler alloy have been investigated. The value of M-s at 4.2 K for the L2(1)-type Co2CrGa alloy is 3.01 mu(B)/f.u., in agreement with the generalized Slater-Pauling line and the theoretical calculation. The Curie temperature T-C and the phase-transformation temperature T-t from the L2(1) to B2-type structure are 495 and 1050 K, respectively. The band calculations disclose that the spin polarization is also relatively high in the B2-type structure, although its estimated T-C is about 100 K lower than that of the L2(1)-type structure. (C) 2004 American Institute of Physics.

In MnIr alloy system, the highest Neel temperature T-N among Mn alloy systems with an Ll(0)-type structure has been confirmed. The electronic specific heat coefficient gamma is of 2-3 mJ mol(-1) K-2 and almost independent of the Ir concentration. It is considered that the Ll(0)-type MnIr alloys are pseudo-gap-type anti ferromagnets from the electrical resistivity and specific heat data, but the value of gamma is larger than that of the Ll(0)-type equiatomic MnPt alloy. These experimental results are in accord with the calculated band structures. (C) 2003 Elsevier B.V. All rights reserved.

印刷中

The electrical resistivity, thermal properties, pressure effect on the Néel temperature and compressibility of Mn3+xRh1-x (x = 0.0, 0.12, 0.20 and 0.32) alloys have been investigated in order to discuss the magnetovolume effects in both ordered and disordered states. The electronic specific heat coefficient γexp of the Mn3Rh ordered alloy is slightly smaller than that of the disordered one, qualitatively consistent with the theoretical calculations. A negative magnetovolume effect is observed below the Néel temperature TN in both the ordered and disordered alloys. Furthermore, the magnetic contribution to the thermal expansion is significant even in the paramagnetic region. That is, the thermal expansion coefficient α in the paramagnetic region shows a large value of about 30 × 10-6 K-1, because of a significant contribution from spin fluctuations. For the Mn3Rh ordered alloy, the pressure shift of the Néel temperature, dTN/dP, is estimated to be about 7.0 K GPa-1. The temperature dependence of α exhibits a pronounced positive peak at TN in accordance with the positive pressure dependence of TN. A large compressibility of 1.4 × 10-2 GPa-1 has been obtained from the change in the lattice constant under pressure.

Electronic and magnetic structures of gamma-phase disordered Mn100-xIrx alloys including L1(2)-type ordered Mn3Ir alloy have been investigated by the first-principles approach using the tight-binding (TB) linear muffin tin orbital (LMTO) method. For the L1(2)-type ordered Mn3Ir alloy, a triangular (T1) magnetic structure is considered to be stable, reflecting in a dip structure around the Fermi level in the density of states. For the gamma-phase disordered Mn3Ir alloy, on the other hand, the most stable structure is suggested to be the 3Q structure among the multiple-Q spin density wave (MSDW) structures. The Neel temperature is estimated to be about 735 K from the effective exchange constant J(0), in good agreement with the experimental value of about 730 K. With decreasing Ir concentration in the gamma-phase disordered Mn100-xIrx alloys, the transition from the 3Q to the 2Q structure takes place in the vicinity of x=13 under the constant lattice parameters with the axial ratio of c/a=1. This critical concentration x is close to the observed concentration at which the axial ratio changes from c/a=1 to c/a&gt;1. However, it should be stressed that these two critical concentrations do not necessarily coincide with each other, that is, the critical concentration of the magnetic structure transition is lower than that of the lattice distortion. This theoretical expectation has been verified by the experimental structural and magnetic data.

The electronic and magnetic structure of Mn3Rh, including noncollinear structures, in the ordered and disordered states have been investigated by the tight-binding linear-muffin-tin orbital method. A magnetic long-range order of the triangular (T1) structure in the ordered state is reflected in a dip around the Fermi level in the density of states. This characteristic feature can be retained in the multiple-Q spin-density-wave (SDW) structures in the disordered alloy, implying that a stable antiferromagnetic order also remains in the disordered alloy. The most stable structure in the disordered alloy is suggested to be the 3Q-SDW structure. From the effective exchange constant, the Néel temperature in the disordered alloy is estimated to be about 680 K, close to the experimental value of about 700 K. Compared to the Néel temperature of pure γ-Mn metal, such a high value is pertinent to the change in the electronic structure caused by the addition of Rh.

The electronic and magnetic structure of Mn3Rh, including noncollinear structures, in the ordered and disordered states have been investigated by the tight-binding linear-muffin-tin orbital method. A magnetic long-range order of the triangular (T1) structure in the ordered state is reflected in a dip around the Fermi level in the density of states. This characteristic feature can be retained in the multiple-Q spin-density-wave (SDW) structures in the disordered alloy, implying that a stable antiferromagnetic order also remains in the disordered alloy. The most stable structure in the disordered alloy is suggested to be the 3Q-SDW structure. From the effective exchange constant, the Neel temperature in the disordered alloy is estimated to be about 680 K, close to the experimental value of about 700 K. Compared to the Neel temperature of pure gamma-Mn metal, such a high value is pertinent to the change in the electronic structure caused by the addition of Rh.

Concentration dependence of the magnetic and electrical properties of MnPt alloy system with a AuCu-I type crystal structure has been investigated in order to discuss the electronic state. Temperature dependence of the electrical resistivity shows a characteristic behavior of gap-type antiferromagnets and the electronic specific heat coefficient gamma is considerably small in consistent with the calculated band structure having a pseudo-gap around the Fermi level. In the vicinity of the equiatomic composition, the Neel temperature is highest, whereas the value of gamma is smallest and increases with decreasing the Neel temperature. From the present experimental results, a close relationship between the electronic state and the antiferromagnetic stability in this alloy system is revealed, in accord with the band calculations. (C) 2002 American Institute of Physics.

Electrical and calorimetric properties of equiatomic MnPd alloy were investigated. For MnPd, the electrical resistivity shows a characteristic behavior of gap-type anti ferro magnets and the electronic specific heat coefficient is remarkably small. These experimental results are in accord with the calculated band structure with a pseudo-gap around the Fermi level. (C) 2002 Elsevier Science B.V. All rights reserved.

The X-ray powder diffraction patterns of Mn1-xOsx (x≥0.36) alloys quenched from 1223 K show the β-Mn structure in which Os atoms preferentially occupy site 1, whereas the patterns of the specimens quenched from 873 K exhibit the α-Mn structure below x = 0.14. Using the resultant data, we have determined the phase diagram of the Mn-Os alloy system for the first time. The Neel temperature of β-Mn1-xOsx (x≥0.36) alloys determined from the magnetic susceptibility increases with increasing Os concentration. The electronic specific heat coefficient, γ, of samples with relatively low Os concentration is considerably large due to spin fluctuations.

The dependence of magnetoresistivity on the temperature and the magnetic field for the antiferromagnetic CePb2 heavy fermion compound has been investigated. In the paramagnetic temperature region above the Néel temperature TN = 3.6 K, the magnetoresistivity exhibits a negative magnetic field dependence due to the Kondo effect. From Schlottmann's scaling for the Kondo impurity model, the characteristic Kondo field and the Kondo temperature TK were found to be about 5.1 T and 0.8 K, respectively. The value of TK is relatively in accord with the value evaluated from the paramagnetic Curie temperature and also the relation between TK/TN and a specific heat jump associated with the magnetic ordering. In the antiferromagnetic temperature region, the magnetoresistivity at 2 K shows a broad peak around 6 T, suggesting that the antiferromagnetic spin configuration is changed under applied magnetic field.

The differential scanning calorimetry (DSC) curves and the temperature dependence of magnetic susceptibility for gamma-MnRh ordered alloys marked peak associated with the magnetic transition. The Neel temperature of Mn7 7Rh2 3 and Mn7 5Rh2 5 ordered alloys is determined to be about 830 and 850 K, respectively. The paramagnetic susceptibility increases with increasing temperature, showing an itinerant electron characteristics. The thermal expansion coefficient becomes small below the Neel temperature due to a targe spontaneous volume magnetostriction, taking about 5 X 10(-6)/K around room temperature. Such alloys with a small thermal expansion coefficient would induce some strain in multilayers because of the difference between the thermal expansion.

Concentration dependence of the Neel temperature of gamma-Mn100-xRux (31 less than or equal to x less than or equal to 37) alloy systems has been investigated. The Neel temperature increases with decreasing Mn concentration in analogy with gamma-Mn-Ir and gamma-Mn-Rh alloys. The Neel temperature of the present, alloy system is the highest in disordered gamma-Mn-TM (TM drop Fe, Ni, Rh, Pd, Ir and Pt) alloys, suggesting that the Neel temperature becomes higher with decreasing the number of 3d electrons in the Mn site.

Investigations of the structure, the electrical resistivity, the magnetic properties and the low-temperature specific heat of PrPb2 have been made. The crystal structure identified by X-ray diffraction for PrPb2 is the body-centered tetragonal MoSi2-type structure with a=3.305 Å and c=16.060 A. The magnetic part of the electrical resistivity for PrPb2 shows a -log T dependence similarly to that of CePb2, but its temperature region is not as wide as that of CePb2. The temperature derivative of the low-temperature magnetic electrical resistivity dρmag/dT and the magnetic susceptibility show a broad peak around 6 K. The magnetic susceptibility exhibits Curie-Weiss behavior at high temperatures, and the effective magnetic moment is 3.68 μB/Pr-mol and practically equals the value of the free trivalent Pr3+ ion. A linear extrapolation in zero field of the C/T versus T2 plot for low-temperature specific heat gives a large electronic specific heat coefficient γ of 656 mJ·mol-1·K-2. Such a large value may be attribute to a Schottky specific heat. The peak around 4.5 K is too small and too broad, compared with a peak representative of a magnetic phase transition. Furthermore, this peak is apparently reduced by applied magnetic fields. Therefore, the peaks observed in the magnetic susceptibility and the specific heat are not correlated with the Néel temperature. © 1998 Elsevier Science S.A.

Magnetic and specific heat measurements of Ce₅Pb₃ compound with a Mn₅Si₃-type structure have been carried out. The magnetic susceptibility shows two peaks at 3.5 and 20.5 K due to the magnetic transitions. The paramagnetic Curie tempertature and the effective magnetic moment obtained from the magnetic susceptibility are -8.2 K and 2.6μ_B, respectively. These results indicate that 4 <i>f</i> electrons are localized in high temperatures and the ground state is antiferromagnetic. The electronic specific heat coefficient, γ, is about 120 mJ/Ce-mol K², and the Debye temperature, θ_D, is estimated to be 150 K. From these results, it is concluded that Ce₅Pb₃ is an antiferromagnetic heavy-fermion compound. The Néel temperature <i>T</i>_N of Ce₅Pb₃ compound is higher than that of other Ce-Pb compounds, which is related to the two kinds of Ce sites.

Temperature dependence of magnetic susceptibility and electrical resistivity of (Ce_1-xLa_x)Pb₂ compounds have been investigated in order to study the effect of substituting La for Ce in a heavy fermion system. The effective magnetic moment estimated from the Curie-Weiss law agrees with that of the theoretical trivalent Ce-ion and independent of the La concentration in high temperatures. The temperature dependence of the magnetic contribution to the electrical resistivity continuously changes from a dense to dilute Kondo regime with increasing La concentration. This behavior would be correlated to a reduction of the Kondo temperature by the substitution of La for Ce.

The present study on the [110]TA1 phonon dispersion relation in a AuCuZn2 alloy reveals that the lattice instability towards the 18R martensite is characteristic of only the Heusler phase existing stably below about 670 K, which is the disordering temperature to the B2-phase. Anomalous peak appearing near zeta=2/3[110] in the Heusler-phase is also examined by neutron elastic scattering experiments in a wide range of temperature. It is evident that such a peak has no relation to the 2/3-dip on the [110] TA, phonon branch observed in the Heusler-phase but it is originated from vacancies existing inherently and regularly in the B2-lattice.