Influence of volume magnetostriction on the T-x phase diagram of shape memory Ni_2+xMn_1-xGa alloys

The phase diagram of structural and magnetic phase transitions of a cubic ferromagnet in the framework of the phenomenological Ginzburg-Landau theory, taking into account the volume change at the structural and magnetic phase transitions, was theoretically investigated. It is shown that the volume magnetostriction significantly influences on the phase diagram of a cubic ferromagnet. In particular, the interval of existence of the coupled magnetic and structural phase transition depends on the value of the volume magnetostriction. This interval for shape memory Ni_{2+ x}Mn_1-xGa Heusler alloys was theoretically evaluated. The theoretical results are in good agreement with the experimental ones.