Electric-field-induced X-ray Nonreciprocal Dichroism in Hematite

TL;DR

This study demonstrates how applying an electric field to hematite induces nonreciprocal x-ray dichroism, revealing higher-order magnetic multipoles and providing a new way to probe hidden magnetic symmetries.

Contribution

The paper introduces electric-field-induced x-ray nonreciprocal dichroism as a method to detect higher-order magnetic multipoles in antiferromagnets, supported by ab-initio simulations.

Findings

Electric field induces nonreciprocal x-ray dichroism in hematite.

The response is linked to magnetic quadrupole and toroidal octupole moments.

Simulations match experimental spectra and reveal multipole origins.

Abstract

Hematite (alpha-Fe2O3) is a prototypical room temperature antiferromagnet whose time-reversal-odd magnetic structure has recently attracted renewed attention. While such magnetic symmetry can be characterized in terms of higher-order multipoles beyond the magnetic dipole, their manifestation in measurable physical phenomena has remained largely elusive. In this work, we investigate x-ray absorption near the Fe K-edge of hematite under an applied electric field, which explicitly breaks space-inversion symmetry. We observe an electric-field-induced x-ray nonreciprocal linear dichroism (E-induced XNLD) that reflects the time-reversal-odd nature of the magnetic order. Numerical simulations based on ab-initio density functional theory reproduce the observed spectra, including their dependence on the antiferromagnetic domain and x-ray polarization. Furthermore, a symmetry-resolved multipole analysis reveals that this response originates from the magnetic quadrupole and the magnetic toroidal octupole induced by the applied electric field. These results demonstrate that electric-field-modulated x-ray absorption provides direct access to the antiferroic order of higher-order multipoles in time-reversal-odd antiferromagnets, thereby establishing a general framework to uncover hidden symmetry properties in magnetic materials.