A phenomenological model of ferromagnetic martensite

The ferromagnetism of the inhomogeneous crystalline structure arising below the temperature of the martensitic phase transition is considered using a phenomenological expression for the Helmholtz free energy of a cubic crystal. The magnetic anisotropy of the martensitic structure is related to the order parameter of the ferroelastic phase transition. The expressions for the static magnetic susceptibility and for the magnetization of the martensite are derived. The theoretical results are compared with the experimental data known for Ni2MnGa alloy. The magnetoelastic constant and the constant of strain-induced magnetic anisotropy of this alloy are estimated from the experimental magnetic field dependence of the magnetization.