Structural and magnetic phase transitions in shape memory ni-mn-ga alloys

Influence of the magnetoelastic interaction on the structural phase transitions in cubic ferromagnets is investigated on the basis of a Ginzburg-Landau theory. It is shown that, for the case of a positive magnetic anisotropy constant, the structural phase transitions are not accompanied by a spin reorientation. In the magnetic state, the high-temperature phase has small deformations caused by magnetostriction. For the case of a strong magnetoelastic coupling, these deformations lead to vanishing of the first-order structural transitions. Corresponding critical points are determined. Due to the magnetoelastic interaction, the first-order magnetic phase transition can occur simultaneously with the first-order structural transformation.