Liu Heyan

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.

Successive phase transformation in ferromagnetic shape memory alloy Co37Ni34Al29 melt-spun ribbons ⁄

The martensitic transformation in Co37Ni34Al29 ribbon is characterized in detail by means of in-situ thermostatic x-ray difiraction and magnetic measurements. The results show a structural transition from the body-centred cubic to martensite with a tetragonal structure during cooling. Comparison between the results of the difiraction intensity with the magnetic susceptibility measurements indicates that the martensitic transformation takes place in several difierent steps during cooling from 273 to 163 K. During heating from 313 to 873 K, the peak width becomes very wide and the intensity turns very low. The ∞-phase (face-centred cubic structure) emerges and increases gradually with temperature increasing from 873 to 1073 K.