Localized magnetic non-uniformities in an antiferromagnet with a system of dislocations

Abstract

In the crystal lattice of an antiferromagnet, dislocations are the origin of specific lines in the field of antiferromagnetic vector I, resembling disclinations in the field of the vector-director for nematic liquid crystals. A single atomic dislocation creates a delocalized non-uniform state – a spin disclination. A “compensated” system of dislocations, a closed dislocation loop in a three-dimensional antiferromagnet or a pair of point dislocations in a two-dimensional antiferromagnet, are shown to form a localized spin non-uniformity, similar to a soliton. For an isotropic or easy-plane antiferromagnet the shape of these solitons is ellipsoidal or circular in three- or two-dimensional cases, respectively. The geometry of a lattice defect differs from that of a soliton; for example, a planar lattice defect, a dislocation loop, produces a nearly spherical three-dimensional spin non-uniformity. In the presence of in-plane anisotropy, a domain wall forms in the easy-plane and ends on the dislocation line (points).

Spin Dynamics in Antiferromagnets with Domain Walls and Disclinations

“…Far from a soliton, the vector l is parallel to the rotation axis. Such localized spin inhomogeneities, which are similar to magnetic droplet solitons, arise due to the presence of either closed dislocation loops in three-dimensional AFMs or point dislocations in twodimensional (2D) AFMs [77]. The application of 2D models makes the analysis substantially simpler.…”

“…(13) are reduced to a static (elliptic) two-dimensional sine-Gordon equation, which is exactly integrable. It has a number of exact solutions that describe different non-uniform states such as vortices, disclinations, and vortex dipoles [77,104,105] (see also book [88]). The results obtained while analyzing 2D models can be applied to describe thin AFM films, the thickness of which is less than all characteristic dimensions of the problem, namely, the distance between dislocations and the exchange length 0 = √︀ / , which determines the domain wall thickness.…”

“…The results obtained while analyzing 2D models can be applied to describe thin AFM films, the thickness of which is less than all characteristic dimensions of the problem, namely, the distance between dislocations and the exchange length 0 = √︀ / , which determines the domain wall thickness. In real AFMs, the exchange length exceeds 10 nm [77]. An investigation of just such films is relevant for their applications in spintronics, because the action of spin current becomes less effective, if the film is thicker than 10 nm.…”

“…The exact analytic solution of this problem in the static case has the simplest form for the isotropic AFM [77]. Let us discuss it in more details, because it also describes the EA AFM in the most interesting case of high frequencies, ∼ 0 .…”

“…A real AFM is always characterized by a certain magnetic anisotropy. For the EA anisotropy, the corresponding analytic solutions (rather cumbersome) were obtained in works [104,105], and they were studied numerically in the framework of the lattice model for the AFM [77]. The analysis showed that if the anisotropy is weak or the disclinations are located close to each other, i.e.…”