| Abstract: | Based on the Landau theory of second-order phase transitions with allowance for interaction between the magnetic subsystem and crystal lattice (magnetophonon interaction, MPI), a consistent thermodynamic model of the invar and covar behavior of ferromagnets with MPI is constructed. Model calculations carried out at real temperatures show that the invar (covar) behavior of ferromagnets results from an optimal relationship between the thermodynamic parameters of the ferromagnetic phase. It is demonstrated that MPI is a fundamentally important factor responsible for the invar and covar effects. With the thermodynamic parameters obeying a certain relationship, the invar behavior of ferromagnets is predicted in a much wider temperature range than in known invars. |
