Condensed Matter Seminar - Altermagnetism: A symmetry-based perspective

Altermagnets, a new class of magnetic systems that combine characteristics of both conventional ferromagnets and antiferromagnets, have recently attracted significant attention. These collinear compensated magnets exhibit spin-split bands, even in the absence of spin-orbit coupling, offering exciting prospects for applications in antiferromagnetic spintronics due to their lack of stray fields, low damping and fast switching times. In this talk, I will introduce altermagnets from a symmetry-based perspective using ideas from Landau theory. Starting from the nonrelativistic limit, this Landau theory goes beyond a conventional magnetic analysis by including spin-space symmetries, providing a simple framework for understanding the key features of this family of materials. We find a set of multipolar secondary order parameters connecting existing ideas about the spin symmetries of these systems, their order parameters, and the effect of nonzero spin-orbit coupling. We account for several features of candidate altermagnets such as MnF2, MnTe, and CuF2 that go beyond symmetry alone, relating the order parameter to key observables such as magnetization, anomalous Hall conductivity, and magnetoelastic and magneto-optical probes. Finally, I will discuss how our framework can be generalized to a broader class of magnetic systems in the zero spin-orbit coupling limit, as well as potentially to noncolinear magnetic structures.