Stress effect on field-induced detwinning strain hysteresis loops in 5M martensite of Ni49.9–Mn28.5–Ga21.6 alloy

This article deals with the magneto-mechanical behaviour of ferromagnetic shape memory alloys like Ni–Mn–Ga. Original experiments of rearrangement of twinned martensite platelets in a single crystal subjected to a magnetic field and a mechanical stress are first presented. A model is then built at the scale of the magnetic domains, i.e. at the relevant scale for the studied coupled phenomena. The multi-scale approach and the thermodynamics of irreversible processes allow to define the macroscopic quantities, to set up the free energy, to propose the evolution laws of the variables and to obtain the expression of the thermodynamic force which is exerted on twins. From its construction, the model of mechanical behaviour obtained has only eight parameters easily measurable in addition (constant of magnetocrystalline anisotropy, saturated magnetization, maximum deformation, initial magnetic susceptibility, etc.).