Spin dynamics in bulk MnNiGa and Mn1.4Pt0.9Pd0.1Sn investigated by muon spin relaxation

We report the results of muon-spin relaxation and magnetometry investigations of bulk Mn1.4Pt0.9Pd0.1Sn and MnNiGa, two materials that have been proposed to host topological magnetic states in thin lamellae (antiskyrmions for Mn1.4Pt0.9Pd0.1Sn and biskyrmions for MnNiGa), and show spin reorientation transitions in the bulk. Our measurements reveal dynamic fluctuations surrounding the magnetic phase transitions in each material. In particular, we demonstrate that the behavior approaching the higher-temperature transitions reflects a decrease in the frequency of dynamics with increasing temperature. At low temperatures the two systems both show spin dynamics over a broad range of frequencies that persist below the respective spin reorientation transitions.