Effect of the interaction between the magnetic and phonon subsystems on the magnetic properties of a ferromagnet: Model calculations

Thermodynamical analysis and model calculations for an isotropic ferromagnet show that inclusion of the interaction between the magnetic and phonon subsystems (in particular, through a magnetization-dependent Debye temperature) causes renormalization of the equation of the magnetic state and a temperature dependence of the thermodynamic coefficients of the Landau expansion, which are usually assumed to be constant. One of the consequences of this dependence is, for example, an experimentally observed difference between the “true” and paramagnetic Curie temperatures of a ferromagnet.