Transverse Magnetization in Spin-Orbit Coupled Antiferromagnets.

Area of Science:

• Condensed Matter Physics
• Magnetism
• Materials Science

Background:

• Antiferromagnets can exhibit transverse magnetization (TM) perpendicular to an applied magnetic field, in addition to conventional parallel magnetization.
• Existing explanations for TM, such as spin canting or cluster magnetic multipolar ordering, lack a comprehensive microscopic theory.
• A general theoretical framework for understanding TM in antiferromagnets is needed.

Purpose of the Study:

• To develop a general microscopic theory for transverse magnetization (TM) in antiferromagnets with cluster magnetic multipolar ordering.
• To investigate the conditions under which TM appears based on symmetry analysis and spin Hamiltonian properties.
• To explore the relationship between TM and observable transport phenomena like the anomalous planar Hall effect.

Main Methods:

• Construction of a general microscopic theory using classical spin Hamiltonians with spin-orbit coupling-induced anisotropy.
• Symmetry analysis to determine the necessary conditions for TM appearance.
• Analysis of spin Hamiltonians to correlate TM with the nature of degenerate ground state manifolds (discrete vs. continuous).

Main Results:

• TM appears when crystalline symmetries are broken, excluding antiunitary mirror, antiunitary twofold rotation, and inversion symmetries.
• TM consistently emerges when the spin Hamiltonian's degenerate ground state manifold is discrete and not symmetry-prohibited.
• TM is generally absent for continuous ground state manifolds, except under specific geometric conditions with single-ion anisotropy.
• Transverse magnetization can induce the anomalous planar Hall effect, offering a method to probe multipolar antiferromagnetic structures.

Conclusions:

• The developed theory provides a microscopic understanding of TM in antiferromagnets with cluster magnetic multipolar ordering.
• Symmetry and ground state degeneracy are key factors governing the appearance of TM.
• The link between TM and the anomalous planar Hall effect offers a novel experimental probe for complex magnetic structures.