The influence of magnetoelastic interaction on structural phase transitions in cubic ferromagnetics

In the framework of the Landau theory of phase transitions, the influence o f the magnetoelastic interaction on structural transitions in cubic ferroma gnetics with a positive first magnetic anisotropy constant is analyzed. It is shown that structural transitions are not accompanied by a reorientation of magnetization in this case. The phase diagrams of such ferromagnetics e ither contain a termination point of the structural transition or a critica l point in which the first-order transition is replaced by a second-order o ne. Magnetoelastic interaction also leads to the appearance of an interval of the ferromagnetic parameters in which a coupled first-order structural-m agnetic transition exists. The phase T-x diagram for Heusler Ni2+xMn1-xGa a lloys is calculated, which is in good agreement with the experimental phase diagram of these alloys. (C) 2001 MAIK "Nauka/Interperiodica".