Anomalous temperature dependence of local magnetic fields in altermagnetic MnTe

TL;DR

This study uses muon-spin spectroscopy to reveal temperature-induced magnetic structure changes in altermagnetic MnTe, highlighting anomalies around 250 K that align with other property variations.

Contribution

First muon-spin spectroscopy investigation of MnTe revealing magnetic structure anomalies near 250 K in an altermagnet.

Findings

Pronounced anomalies in muon-spin depolarisation below room temperature

Emergence of a second internal magnetic field around 250 K

Magnetic structure change coinciding with transport property variations

Abstract

Altermagnets are a novel type of magnetic system that has a spin-polarised electric band structure in the absence of a net magnetic moment, leading to exciting prospects in potential device applications. Hexagonal MnTe, a prototypical altermagnet, has arguably shown the most properties consistent with theoretical predictions, including an anomalous Hall effect despite no net magnetisation, and strong altermagnet-induced spin splitting in the electronic band structure. Here we present muon-spin spectroscopy measurements of a single crystal of MnTe. Below room temperature we observe pronounced anomalies in the muon-spin depolarisation, as well as the onset of a second, non-proportional internal field in the absence of an applied field. These findings point to a change in the magnetic structure around $T\simeq250$ K, which coincides with other changes in reported properties, such as transport.