Magnetic phases of skyrmion-hosting GaV${}_4$S${}_{8-y}$Se${}_y$ ($y=0,2,4,8$) probed with muon spectroscopy

Abstract

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.