Luo Hongzhi

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.

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.