On the theory of the formation of equilibrium domain structure in antiferromagnets

A model is proposed which describes the formation and reversible rearrangement of the equilibrium domain structure in bulk antiferromagnets with a rather strong magnetoelastic coupling. The model is based on the assumed existence of a microscopic ordering of a tensor nature—the microstress tensor that arises due to magnetoelastic coupling during the formation of the magnetic moment. It is necessary to take such a parameter into account for adequate description not only of the macroscopic internal stresses and the spontaneous strains corresponding to them but also of the microstructure of the crystal (e.g., the domain structure). The microstresses arising locally in each unit cell are equivalent, from a formal standpoint, to elastic dipoles, and they create long-range fields whose contribution to the free energy of the crystal is analogous to that of the magnetostatic energy in ferromagnets and favors a decrease in the macroscopic strain of the sample through the formation of an equilibrium domain structur...