86th CEMS Colloquium

Title

Functional topological antiferromagnet

Abstract

Chiral antiferromagnets Mn₃X (X=Sn and Ge) exhibit large magnetoelectric, thermoelectric, and optical responses such as anomalous Hall effect (AHE), anomalous Nernst effect (ANE), and magneto-optical Kerr effect (MOKE); their magnitudes reach almost the same as those of ferromagnetic metals. All of these characteristic properties of Mn₃X imply that the spin Hall effect (SHE) could also occur. Our recent study demonstrated that a novel type of contribution to the SHE (magnetic SHE, MSHE) and the inverse SHE (MISHE) absent in nonmagnetic materials could be dominant in the antiferromagnets, Mn₃X. We attribute this dominant magnetic mechanism to the momentum-dependent spin splitting produced by the noncollinear magnetic order,i.e., the cluster magnetic octupole (CMOP), comprising two sets of three spin sublattices. Moreover, the cluster magnetic octupole takes ferroic order on the Kagome lattice, macroscopically breaking the time-reversal symmetry. Previous studies also revealed that the cluster magnetic octupole, not the magnetic dipole, plays an essential role as the magnetic order parameter for antiferromagnetic domains and domain walls.

In the first half of this talk, we will introduce our recent experimental results on the magnetic spin Hall effects (MSHE), particularly angular dependent spin densities appearing on the surface of a focused ion beam fabricated Mn₃Sn epitaxial thin slab. We will discuss the new functionality for magnetic manipulation we could obtain from the MSHE. In the second half, we will discuss the electrical nucleation, displacement, and detection of antiferromagnetic domain walls (AFDWs) consisting of the CMOPs. We will also show some of our recent MOKE measurements for Mn₃Ge to discuss the magnetic domain structures. Our findings could provide a guiding principle for engineering the AFDW structure in the chiral antiferromagnetic materials.