The problem of choosing of the group of symmetries of paramagnetic phase in the theory of magnetic phase transitions and the exchange multiplets

Abstract

It is shown that for the theoretical description of the magnetic and structural phase transitions in the magnetics with magnetoactive ions of transition metals within the framework of the Landau theory of phase transitions the exchange group GxO(3) should be chosen as the group of symmetry of paramagnetic phase. Such a choice allows to describe the transition from the paramagnetic phase into the isotropic magnetically ordered phase (at Tc), and the spin-orbit transition from the isotropic into the anisotropic phase (at T<Tc). The exchange multiplet describes the spin-orbit phase transition.