We present the results of a muon-spin spectroscopy investigation of ${\mathrm{GaV}}_4{\mathrm{S}}_{8-y}{\mathrm{Se}}_y$ with $y=0,2,4$, and 8. Zero-field measurements suggest that ${\mathrm{GaV}}_4{\mathrm{Se}}_8$ and ${\mathrm{GaV}}_4{\mathrm{S}}_8$ 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 behavior 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 ${\mathrm{GaV}}_4{\mathrm{Se}}_8$, 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.

• Received 4 June 2018
• Revised 20 July 2018

DOI:https://doi.org/10.1103/PhysRevB.98.054428