Influence of Ga doping on the magnetic anisotropy of the kagome-lattice magnet TmMn6Sn6.

The kagome-lattice compounds RMn6Sn6 (R is a rare earth element), where the Mn atoms form a kagome net in the basal plane, are currently attracting a great deal of attention as they’ve been shown to host complex magnetic textures and electronic topological states strongly sensitive to the choice of the R atom. Among the magnetic R atoms, TmMn6Sn6 orders with the easy-plane magnetization forming a complex magnetic spiral along the c-axis. Previous neutron studies carried on polycrystalline samples have shown that Ga doping changes the magnetic anisotropy from easy-plane to easy-axis. Here we present magnetic and magnetotransport measurements on a single crystal and first principles calculations in the doping series TmMn₆Sn_6-xGa_x. We find that the magnetic properties are highly sensitive even to a small concentration of Ga. At small Ga concentrations, the in-plane anisotropy is maintained, which gradually changes to the out-of-plane anisotropy with increasing Ga. We will discuss these observations with respect to the effect of modification of the Tm crystal field, introduced by Ga doping.