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 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.

Martensitic phase transitions in a stressed cubic crystal are studied by means of Landau theory with a twocomponent order parameter. The stress-temperature phase diagram is analyzed theoretically and is shown to consist of six essentially different regions isolated by the liability lines of austenite, tetragonai martensitic and orthorhombic martensitic phases. The triple point is also present in the phase diagram. The role of the cubic term in the Landau-Ginzburg potential in the description of the phase transition properties is emphasized.

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