Yishui Zhou (FZ Jülich and TU Munich) - Complex magnetic order and novel field-induced magnetic phases in topological kagome metals

Abstract: Magnetic topological metals with a kagome lattice have attracted tremendous attention because they are a promising platform for investigating the interplay between magnetism, topology and geometric frustration. Among them, the RT6Sn6 (R= rare-earth, T= transition metal) series stands out for its unique crystal structure with a kagome bilayer formed by T and a triangular layer formed by R. In our work, we systematically investigated complex magnetic order and emergent field-induced magnetic phases in RMn6Sn6 and RV6Sn6 via single-crystal growth, XRD, in-house characterisations of magnetic and topological properties, and comprehensive single-crystal neutron diffraction measurements. Magnetic anisotropies vary between different compounds because of the single-ion anisotropy of R ion and R-Mn interaction. The neutron diffraction was performed on RMn6Sn6 (R=Er, Tm) under zero-field and revealed the thermal evolution of the magnetic structure. Besides, a transition from the incommensurate spiral phase to the commensurate ferrimagnetic or lock-in phases at low temperatures is also determined. A molecular-magnetic field model is also introduced to describe the induced ordering behavior of rare-earth moments by Mn. Under applied magnetic fields, both compounds exhibit rich phase diagrams, and the emergence of topological Hall effects was observed and is likely linked to various field-induced non-coplanar magnetic order, such as the transverse conical spiral state that was directly confirmed by our neutron diffraction investigations. In the RV6Sn6 series, where V is non-magnetic, the ground-state magnetic structure compounds of R = Tb–Er were studied via single-crystal neutron diffraction and revealed the collinear ferromagnetic order R = Tb, Dy, and Ho while A-type antiferromagnetic order for R = Er. Our work thus provides a comprehensive understanding of the interplay between magnetism and topology in magnetic topological kagome metals, and paves the way for the engineering of magnetic kagome materials for future exploration of topological quantum phases and possible applications.