A model of phase transition from austenite to martensite in single-crystal NiMnGa alloys

A model is presented for the description of shape memory effect due to the thermoelastic martensite transformation induced by temperature, stress and magnetic field in ferromagnetic NiMnGa alloys. A cosine model on the basis of thermodynamic principle is developed to describe the structural distortion of the lattice in the complex coupled field. The magnetic-field-induced stress is introduced and the equivalence principal is employed for the mechanical and magnetoelastic deformation to represent the reorientation of the martensitic variants. The comparison between the theoretical and experimental results shows that the theory provides a good quantitative description of the material peculiar behavior.