Phase diagrams of a shape-memory cubic ferromagnet represented as stress versus temperature graphs

In the framework of the phenomenological Landau theory, the structural and magnetic phase transitions in cubic ferromagnets exhibiting the shape memory effect in the presence of an elastic stress aligned with the [001] axis are theoretically studied. It is shown that, at a negative combination of the third-order elastic moduli, the tetragonal and rhombic structural phases with the magnetization oriented along the [001] axis and the rhombic phase with the magnetization in the (001) plane are realized in a ferromagnet. The tetragonal phase with the magnetization oriented along the [001] axis and the rhombic phase with the magnetization in the (001) plane may exist at a positive combination of the third-order elastic moduli. Under the change of the external stress sign, the first-order structural and magnetic orientational phase transition occurs. Structural phase transitions may be of the first and second orders.