Magnetic structures and reorientation transitions in noncentrosymmetric uniaxial antiferromagnets

TL;DR

This paper develops a phenomenological theory for magnetic states in noncentrosymmetric tetragonal antiferromagnets, revealing new incommensurate structures, reorientation transitions, and defect configurations influenced by Dzyaloshinskii-Moriya interactions.

Contribution

It introduces a comprehensive model incorporating Lifshitz-invariants to describe complex magnetic structures and phase transitions in low-symmetry antiferromagnets.

Findings

Identification of chiral inhomogeneous magnetic structures.

Prediction of new incommensurate magnetic phases.

Analysis of field-induced reorientation transitions.

Abstract

A phenomenological theory of magnetic states in noncentrosymmetric tetragonal antiferromagnets is developed, which has to include homogeneous and inhomogeneous terms (Lifshitz-invariants) derived from Dzyaloshinskii-Moriya couplings. Magnetic properties of this class of antiferromagnets with low crystal symmetry are discussed in relation to its first known members, the recently detected compounds Ba2CuGe2O7 and K2V3O8. Crystallographic symmetry and magnetic ordering in these systems allow the simultaneous occurrence of chiral inhomogeneous magnetic structures and weak ferromagnetism. New types of incommensurate magnetic structures are possible, namely, chiral helices with rotation of staggered magnetization and oscillations of the total magnetization. Field-induced reorientation transitions into modulated states have been studied and corresponding phase diagrams are constructed. Structures of magnetic defects (domain-walls and vortices) are discussed. In particular, vortices, i.e. localized non-singular line defects, are stabilized by the inhomogeneous Dzyaloshinskii-Moriya interactions in uniaxial noncentrosymmetric antiferromagnets.