Possibility of formation and reversible rearrangement of equilibrium domain structure in antiferromagnets

Abstract

It is shown that the magnetoelastic interaction can play a substantial role in the formation of the equilibrium domain structure in antiferromagnets having two or more equivalent easy directions of the axis of magnetic anisotropy. It is demonstrated with the use of the methods of nonlinear theory of elasticity in the framework of a phenomenological model that the surface of the crystal can and does serve as a source of fictitious “elastic charges” of incompatibility, which have consequences analogous to those of the magnetostatic charges that arise on the surface of ferromagnetic crystals and lead to the formation of domains. Here the surface of the crystal is treated as a special phase with its own magnetic, elastic, and magnetoelastic properties. The field of the “elastic charges” is long-ranged, and, accordingly, its contribution to the stray (“detwinning”) energy, which plays the main role in the formation of the equilibrium domain structure, is proportional to the volume of the sample rather than its surface area. The formation of the domain structure is nothing more than the restoration of the initial global symmetry of the crystal in those cases when the phase transformation that breaks this symmetry is described by an order parameter which is conjugate to the shear strain. The conditions for the absence of “elastic charges” inside the sample impose certain restrictions on the morphology of the magnetoelastic domain structure in antiferromagnets. It is shown how the character of the equilibrium state of the crystal is influenced by disclinations arising at places where three or more domains come together.