Magnetic-field-induced superelasticity of ferromagnetic thermoelastic martensites: Experiment and modeling

The superelastic effect under constant magnetic fields exhibited by the Ni-Mn-Ga ferromagnetic thermoelastic martensites with single-variant and polyvariant microstructure is studied experimentally and theoretically. The formerly proposed statistical model of the magnetostrain effect in the ferromagnetic martensite is modified for the theoretical description of the superelastic stress-strain dependence under magnetic field. The mechanical stress, which is equivalent to the internal stress induced by the magnetic field, is determined by fitting the theoretical stress-strain curves to the experimental results. A quadratic dependence of the field-induced stress on the value of the magnetization of martensite is found. This dependence supports the model assumption that a magnetoelastic interaction causes the magnetostrain effect.