Altermagnets versus Antiferromagnets

Abstract: Altermagnets are metals with a momentum-dependent spin splitting of electron bands due to a specific crystal structure, which is invariant under time reversal only in combination with rotations and reflections. The developed phenomenological approach makes it possible to obtain a spectrum of electron bands in an altermagnet corresponding to an antiferromagnet with the same symmetry. The anomalous Hall effect is an inherent property of substances whose electron band dispersion is characterized by the Berry curvature. Calculations of the Berry curvature were performed for altermagnet analogs of collinear antiferromagnet, weak ferromagnetic antiferromagnet, and ferrimagnetic structures. It was shown that in the specific cases under consideration, the anomalous Hall effect in the absence of an external magnetic field is possible only in the state of a weak ferromagnet.