J. Phys. IV France 112 (2003) 907
Displacive phase transformations and magnetic properties in Ni-Mn-Ga ferromagnetic shape memory alloysK. Tsuchiya1, A. Tsutsumi1, H. Nakayama1, S. Ishida2, H. Ohtsuka3 and M. Umemoto1
1 Toyohashi University of Technology, Department Production Systems Engineering, Toyohashi, Aichi 441-8580, Japan
2 Kagoshima University, Department Physics, Faculty of Science, Kagoshima 890-0065, Japan
3 National Institute for Materials Science, Material Engineering Laboratory, Tsukuba, Ibaraki 305-0003, Japan
Composition dependence of displacive phase transformation behavior has been studied on Ni-Mn-Ga ferromagnetic shape memory alloys. A good correlation was found between the valence electron density ( e/a) and martensitic transformation temperature, intermediated phase transformation temperature and the Curie temperature, as well as the values of magnetization. Crystal structure of martensite also changes with e/a. Transformation from the parent phase to the intermediate phase and then to the martensite phase were observed in-situ by TFM. The intermediate phase was characterized by the satellite spots at 1/6g 220 positions irrespective of the structure of martensite obtained by the further cooling. Composition dependence of the martensitic transformation temperature was compared with the prediction of electronic band structure calculation.
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