The derivation of the Landau–Lifshitz equations for antiferromagnets with two types of magnetic ions of different mass is presented. The contribution of the difference in interaction potentials of different subsystems is discussed (the difference in masses, potentials, and magnetic moments corresponds to ferrimagnets). The derivation of the exchange interaction and the contribution of the anisotropy energy is based on the use of the ‘‘ x, y, z ’’ model. The derivation of the Dzyaloshinskii–Moriya interaction contribution is considered. Two mechanisms of the emergence of the Dzyaloshinskii–Moriya interaction are investigated: one is caused by the violation of inversion symmetry in the lattice, and the other is associated with the existence (and displacement) of a ligand ion, which is represented by an oxygen ion. In addition, the possibility of anisotropy of the Dzyaloshinskii–Moriya interaction is taken into account.
P. A. Andreev (Mon,) studied this question.