Experimental Evidence of N\'eel-order-driven Magneto-optical Kerr Effect in an Altermagnetic Insulator

TL;DR

This study demonstrates that the magneto-optical Kerr effect in hematite is primarily driven by Nel order, revealing the altermagnetic origin of MOKE and highlighting altermagnets as promising magneto-optical materials.

Contribution

It provides experimental and theoretical evidence that Nel order dominates MOKE in hematite, clarifying the altermagnetic origin of the effect.

Findings

Nel order contribution dominates MOKE signal

Magnetization contribution is negligible

First-principles calculations support Nel contribution

Abstract

The magneto-optical Kerr effect (MOKE) is investigated in hematite, a collinear antiferromagnetic insulator, across a broad wavelength spectrum. By combining the optical measurements with magnetometry results, we unambiguously demonstrate that the N\'eel-order contribution dominates the MOKE signal, while contributions from net magnetization and external magnetic fields are negligible. This conclusion is quantitatively supported by first-principles calculations, and qualitatively by a symmetry analysis that the N\'eel contribution appears at the first order in spin-orbit coupling while the magnetization contribution starts only at the third order. This study clarifies the altermagnetic origin of the pronounced MOKE in hematite, underscoring the potential of altermagnets as a promising new class of magneto-optical materials.