Observation of Altermagnetic Order Switching in Bulk MnTe by Polarized Neutron Diffraction

TL;DR

This study uses polarized neutron diffraction to directly observe and demonstrate the controllable switching of altermagnetic order and weak ferromagnetism in bulk MnTe, revealing new magnetic phenomena.

Contribution

First direct detection of altermagnetic order in MnTe using polarized neutron diffraction and demonstration of its switchability with small magnetic fields.

Findings

Detected a net Néel vector in bulk MnTe.

Observed coupling between altermagnetic order and weak ferromagnetism.

Showed that both orders can be switched by milli-Tesla magnetic fields.

Abstract

Altermagnetic order, characterized by the N\'{e}el vector, breaks time-reversal symmetry (TRS) even in the nonrelativistic limit. Although spin-polarized and anomalous transport phenomena emerge with this order, they are mutually compensated by TRS-connected antiphase domains with opposite N\'{e}el vectors. Here we employ polarized neutron diffraction to directly probe the altermagnetic order in MnTe. Pronounced nuclear-magnetic interference terms were observed, providing direct evidence of a net N\'{e}el vector in the bulk crystal. Moreover, a weak ferromagnetic moment (WFM), originating from relativistic spin-orbit coupling, was found to be coupled with the altermagnetic order. Both the altermagnetic order and the WFM can be switched by milli-Tesla-scale magnetic field cooling.