Microscopic theory of spin reorientations- thermodynamics and nucleation phenomenon

Stability of thermodynamic states is analysed for the heterophase model with spin reorientations, earlier proposed by the authors. Reorientation points and Curie points are determined and the critical indices are found in these points. The behaviour of the main thermodynamic characteristics is investigated. The nucleation phenomenon is considered, which is shown to be able to develop both continuously and stepwise. A classification of magnets based on the phase transition sequence in them is proposed.