Microscopic theory of spin reorientations - heterophase approach and basic model

A new approach to the description of magnetic reorientation transitions is proposed. Unlike others, this approach allows the consequent microscopic formulation of the problem to be combined with taking into account heterophase states which occur in magnetics and are a mixture of phases with different directions of magnetization. The proposed theory is illustrated by an exactly solved model which is a heterophase generalization of the anisotropic Heisenberg model with long-range interaction.