Revealing the Altermagnetism in Hematite via XMCD Imaging and Anomalous Hall Electrical Transport

TL;DR

This paper provides experimental evidence that hematite exhibits altermagnetism, characterized by unconventional transport properties like anisotropic anomalous Hall effect, confirmed through advanced imaging and transport measurements supported by theoretical calculations.

Contribution

It is the first to experimentally confirm hematite as an altermagnet using combined imaging, transport measurements, and theoretical analysis.

Findings

Visualization of Ne9el vector coupling to crystal orientation

Observation of anisotropic anomalous Hall effect with sign inversion

Theoretical explanation of spin and symmetry interplay driving AHE

Abstract

Altermagnets are a class of magnetic materials that exhibit unconventional transport properties, such as an anomalous Hall effect, despite having compensated sublattice magnetic moments. In this study, we report fundamental experimental evidence of the altermagnetic nature of hematite ($\alpha$-\ch{Fe2O3}), combining electrical transport with advanced XPEEM imaging with linear and circular dichroism contrast. Our measurements directly visualize the N\'eel vector's coupling to the crystal orientation, confirming hematite's altermagnetic order and its symmetry-driven transport behavior. Transport measurements reveal an anisotropic AHE with a pronounced crystal orientation dependence, including a sign inversion for specific N\'eel vector alignments. Supported by first-principles theoretical calculations, we explain how the interplay between collinear spin and crystal symmetry breaking drives the observed anomalous Hall effect. These findings establish hematite as an altermagnet, paving the way for experimental identification of altermagnetic materials and their integration into spintronic technologies.