Field-induced spin reorientation transitions in antiferromagnetic ring-shaped spin chains

TL;DR

This paper theoretically explores how curvature in ring-shaped antiferromagnetic spin chains influences spin reorientation transitions under strong magnetic fields, revealing geometry-dependent phase transitions and weak ferromagnetic responses.

Contribution

It introduces a theoretical analysis of curvature effects on spin reorientations and phase transitions in achiral antiferromagnetic rings, highlighting geometry-governed phenomena.

Findings

Identification of a geometry-governed helimagnetic phase transition.

Curvature-induced Dzyaloshinskii-Moriya interaction affects transition order.

Spatial inhomogeneity leads to weak ferromagnetic response.

Abstract

Easy axis antiferromagnets are robust against external magnetic fields of moderate strength. Spin reorientations in strong fields can provide an insight into more subtle properties of antiferromagnetic materials, which are often hidden by their high ground state symmetry. Here, we investigate theoretically effects of curvature in ring-shaped antiferromagnetic achiral anisotropic spin chains in strong magnetic fields. We identify the geometry-governed helimagnetic phase transition above the spin-flop field between vortex and onion states. The curvature-induced Dzyaloshinskii-Moriya interaction results in the spin-flop transition being of first- or second-order depending on the ring curvature. Spatial inhomogeneity of the N\'eel vector in the spin-flop phase generates weak ferromagnetic response in the plane perpendicular to the applied magnetic field. Our work contributes to the understanding of the physics of curvilinear antiferromagnets in magnetic fields and guides prospective experimental studies of geometrical effects relying on spin-chain-based nanomagnets.