We present the results of a muon-spin spectroscopy investigation of GaV$_4$S$_{ 8-y}$Se$_{ y}$ with $y=0, 2, 4$ and 8. Zero-field measurements suggest that GaV$_{ 4}$Se$_{ 8}$ and GaV$_{ 4}$S$_{ 8}$ have distinct magnetic ground states, with the latter material showing an anomalous temperature-dependence of the local magnetic field. It is not possible to evolve the magnetic state continuously between these two systems, with the intermediate $y=2$ and $4$ materials showing glassy magnetic behaviour at low temperature. The skyrmion lattice (SkL) phase is evident in the $y=0$ and 8 materials through an enhanced response of the muon-spin relaxation to the emergent dynamics that accompany the SkL. For our polycrystalline samples of GaV$_4$Se$_{ 8}$, this enhanced dynamic response is confined to a smaller region of the magnetic field-temperature phase diagram than the previous reports of the SkL in single crystals.
Categories: cond-mat.mtrl-sci cond-mat.str-el