Wu Guang-Heng

Electronic structure and magnetic properties of Fe2YSi (Y = Cr, Mn, Fe, Co, Ni) Heusler alloys: a theoretical and experimental study

A series of Fe2YSi (Y = Cr, Mn, Fe, Co, Ni) alloys were synthesized and their electronic and magnetic properties were studied both theoretically and experimentally. In particular, a novel Heusler alloy Fe2CrSi single phase was synthesized by means of the melt-spinning method. First principles FLAPW calculations were performed on Fe2YSi alloys. Based on the results, Fe2CrSi is predicted to be a half-metallic ferromagnet with a spin moment of 2?B/f.u. and a gap of 0.42?eV. Fe2MnSi is also half-metallic in the ferromagnetic state. The saturation magnetic moments at 5?K for this series of alloys fit the theoretical calculations well. Specifically, the saturation magnetic moment of Fe2CrSi is 2.05?B/cell, which agrees with the ideal value of 2?B derived from the Slater?Pauling rule. The Curie temperatures of Fe2YSi alloys are all higher than 500?K except for Fe2MnSi, which has a TC below room temperature. Finally, the effect of lattice distortion on the electronic and magnetic properties of Fe2CrSi and Fe2CoSi was studied. It is found that Fe2CrSi is half-metallic from ?3% to +1% uniform lattice distortion, and this character is preferred in systems containing large strain, such as melt-spun ribbons or thin films.

Effect of rapid solidification on the site preference of Heusler alloy Mn2NiSb

The site preference of Mn atoms in Heusler alloy Mn2NiSb can be influenced obviously by different preparing methods. Mn atoms enter the A and B sites after arc-melting and subsequent annealing, and form an Hg2CuTi-type of structure. However, after melt-spinning, the Mn atoms tend to occupy the (A, C) sites and form the Cu2MnAl-type of structure. The electronic structure calculations suggest that the Hg2CuTi-type of structure is lower in energy than the Cu2MnAl one and more stable. The lattice constant of the former is a bit larger than the latter one, agreeing with experimental results. Ferromagnetism is observed in Mn2NiSb with both structures. Calculations give a total moment of 4.21 μB for the Hg2CuTi-type of structure and 3.93 μB for the Cu2MnAl-type one. These results fit the saturation magnetization at 5 K quite well. The difference between the Curie temperatures of the bulk and ribbon samples is about 77 K.

Synthesis and Magnetic Properties of Gd3 (Fe, Co, Cr)29 Compounds

Formation and magnetic properties of the Gd3Fe29-x-yCoxCry compounds have been investigated. It has been found that formation of single-phase compounds Gd3Fe29-x-yCoxCry with the Nd3(Fe,Ti)29-type structure depends strongly on the content of the stabilizing element Cr, and the solid-solution limit of Co in Gd3Fe29-x-yCoxCry compounds increases with Cr content. Pure Co-based Gd3Co29-yCry compounds with the Nd3(Fe,Ti)29-type structure have been successfully synthesized with y = 6.5 and 7.0. The Curie temperature TC of Gd3Fe29-x-yCoxCry compounds increases with increasing Co content x at fixed y, whereas the increase of the Cr content leads to an obvious decrease of TC of the Gd3Co29-yCry compounds. Composition dependence of the saturation magnetization at 5 K reaches a maximum around x = 7.5 and y = 4. It is worth noting that substitution of Co for Fe results in a significant change of magnetocrystalline anisotropy of the Gd3Fe29-x-yCoxCry compounds and changes the easy magnetization direction from basal-plane to easy-axis when x>10 and y = 4.

Point contact Andreev reflection measurement of the spin polarization of ferromagnetic alloy NiFeSb

We have studied the temperature-dependent and barrier-strength-dependent Andreev reflection tunnelling spectroscopy with point contacts consisting of the newly synthesized half-metallic alloy NiFeSb and a Nb tip. By fitting the data to the generalized Blonder-Tinkham-Klapwijk theory, a spin polarization P = 0.52 has been obtained.

Magnetocrystalline Anisotropy and Magnetoelasticity of Preferentially Oriented Martensitic Variants in Ni52Mn24Ga24 Single Crystals

The magnetocrystalline anisotropy and magnetoelasticity of preferentially oriented martensitic variants in an off-stoichiometric Ni52Mn24Ga24 single crystal have been investigated. We found that the easy magnetization direction of the martensite phase is the [110] direction, and the hard magnetization exhibited in [001], the growth direction of single crystals. The temperature dependence of the anisotropy fields and constants of Ni52Mn24Ga24 have been determined. It was found that, at the martensite phase, the anisotropy field increases monotonically with decreasing temperature, but the anisotropy constant first increases rapidly and then the increasing rate becomes smaller and smaller. Based on a previous model, the present results suggest that the competition between the Zeeman energy and the magnetocrystalline anisotropy energy is mainly responsible for the magnitude of magnetic-field-induced strain in this material.

Effects of Cu on the martensitic transformation and magnetic properties of Mn50Ni40In10 alloy

The structures, the martensitic transformations, and the magnetic properties are studied systematically in Mn50Ni40?xCuxIn10, Mn50?xCuxNi40In10, and Mn50Ni40In10?xCux alloys. The partial substitution of Ni by Cu reduces the martensitic transformation temperature, but has little influence on the Curie temperature of austenite. Comparatively, the martensitic transformation temperature increases and the Curie temperature of austenite decreases with the partial replacement of Mn or In by Cu. The magnetization difference between the austenite phase and the martensite phase reaches 70 emu/g in Mn50Ni39Cu1In10; a field-induced martensite-to-austenite transition is observed in this alloy.

Structure and magnetic properties of (Nd1?xErx)3Fe25Cr4.0 (0 ? x ? 0.8) compounds

The structure and magnetic properties of (Nd1-xErx)(3)Fe25Cr4.0 compounds with x = 0-0.8 have been investigated using x-ray powder diffraction (XRD) and magnetic measurements. It has been found that all the compounds crystallize in a Nd-3(Fe,Ti)(29)-type structure. Substitution of Er for Nd leads to a contraction of the unit-cell volume. The Curie temperature, T, and the saturation magnetization, M-s, of (Nd1-xErx)(3)Fe25Cr4.0 decrease monotonically with increasing Er content. The easy magnetization direction (EMD) of Nd3Fe25Cr4.0 at room temperature is close to the [040] direction but may be a little out of the basal plane. With increasing Er content, the EMD changes closer to the [40-2] direction and the tilt angle increases. Both the XRD patterns and ac susceptibility indicate the appearance of a spin reorientation for x = 0-0.4 as the temperature decreases from room temperature to 77 K. The spin reorientation temperature, T-sr, increases monotonically with increasing Er content from 158 K for x = 0 to 198 K for x = 0.4. A first order magnetization process (FOMP) occurs for all the compounds, and the critical field of the FOMP decreases with increasing Er content from 6.6 T for x = 0 to 2.0 T for x = 0.7.

NEAR-RESONANT RAMAN-SCATTERING FROM GAAS/ALAS SUPERLATTICES

The outstanding hard-magnetic properties are reported of Sm3Fe28.1-xCoxMo0.9 compounds with x=12, 14, 16. In this alloy system, only a small amount of Mo is needed to stabilize the 3:29 structure so that the magnetic properties are not seriously affected by the presence of this nonmagnetic element. Substitution of Co for Fe leads to a significant increase of the magnetic anisotropy, and for x greater than or equal to 14 the easy magnetization direction changes from easy plane to the easy axis. In this alloy system, the compound Sm3Fe12.1Co16Mo0.9 is a very promising candidate for permanent magnet applications. Its room temperature saturation magnetization (mu(0)M(s)=1.5T) and anisotropy field (B-an=6.5 T) are comparable to the values for Nd2Fe14B (mu(0)M(s)=1.6 T and B-an=7 T). However, the Curie temperature of Sm3Fe12.1Co16Mo0.9 is 1020 K, which is appreciably higher than that for Nd2Fe14B (T-C=588 K).

Mn和Fe掺杂对尖晶石氧化物Co 2 MnO 4 结构和磁性的影响

以金属盐及柠檬酸为原料, 采用溶胶–凝胶法制备了尖晶石氧化物Co 2- x Mn 1+ x O 4 和Co 2- x Fe x MnO 4 系列, 通过XRD、FT-IR及PPMS等手段研究了Co 2 MnO 4 及系列掺杂样品的成相、结构、磁性等特征。结果表明, Co 2- x Mn 1+ x O 4 系列在 x ＜0.6时, 呈单相立方结构, 晶格常数和磁性随着Mn掺杂量的增加而增大, x ≥0.6时逐渐向四方结构转化, 磁性下降, 并呈现磁化强度不易饱和的特征; Co 2- x Fe x MnO 4 系列样品在 x ＜1.75成分范围内均可保持立方结构, 且晶格常数和磁性都随着x增大而提高。这些变化主要是由于掺杂原子尺度及磁矩均大于原有元素, 掺杂后样品内部的磁性相互作用有所增强。以金属盐及柠檬酸为原料, 采用溶胶–凝胶法制备了尖晶石氧化物Co 2- x Mn 1+ x O 4 和Co 2- x Fe x MnO 4 系列, 通过XRD、FT-IR及PPMS等手段研究了Co 2 MnO 4 及系列掺杂样品的成相、结构、磁性等特征。结果表明, Co 2- x Mn 1+ x O 4 系列在 x ＜0.6时, 呈单相立方结构, 晶格常数和磁性随着Mn掺杂量的增加而增大, x ≥0.6时逐渐向四方结构转化, 磁性下降, 并呈现磁化强度不易饱和的特征; Co 2- x Fe x MnO 4 系列样品在 x ＜1.75成分范围内均可保持立方结构, 且晶格常数和磁性都随着x增大而提高。这些变化主要是由于掺杂原子尺度及磁矩均大于原有元素, 掺杂后样品内部的磁性相互作用有所增强。

Structure and Magnetic Property of Fe and Mn Doped Spinel Co

以金属盐及柠檬酸为原料, 采用溶胶–凝胶法制备了尖晶石氧化物Co 2- x Mn 1+ x O 4 和Co 2- x Fe x MnO 4 系列, 通过XRD、FT-IR及PPMS等手段研究了Co 2 MnO 4 及系列掺杂样品的成相、结构、磁性等特征。结果表明, Co 2- x Mn 1+ x O 4 系列在 x ＜0.6时, 呈单相立方结构, 晶格常数和磁性随着Mn掺杂量的增加而增大, x ≥0.6时逐渐向四方结构转化, 磁性下降, 并呈现磁化强度不易饱和的特征; Co 2- x Fe x MnO 4 系列样品在 x ＜1.75成分范围内均可保持立方结构, 且晶格常数和磁性都随着x增大而提高。这些变化主要是由于掺杂原子尺度及磁矩均大于原有元素, 掺杂后样品内部的磁性相互作用有所增强。以金属盐及柠檬酸为原料, 采用溶胶–凝胶法制备了尖晶石氧化物Co 2- x Mn 1+ x O 4 和Co 2- x Fe x MnO 4 系列, 通过XRD、FT-IR及PPMS等手段研究了Co 2 MnO 4 及系列掺杂样品的成相、结构、磁性等特征。结果表明, Co 2- x Mn 1+ x O 4 系列在 x ＜0.6时, 呈单相立方结构, 晶格常数和磁性随着Mn掺杂量的增加而增大, x ≥0.6时逐渐向四方结构转化, 磁性下降, 并呈现磁化强度不易饱和的特征; Co 2- x Fe x MnO 4 系列样品在 x ＜1.75成分范围内均可保持立方结构, 且晶格常数和磁性都随着x增大而提高。这些变化主要是由于掺杂原子尺度及磁矩均大于原有元素, 掺杂后样品内部的磁性相互作用有所增强。