Chen Jing-Lan

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.

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.