Evidence of a cluster spin-glass phase in the skyrmion-hosting GaMo4S8 compound

Abstract

GaMo₄S₈, is a poorly known lacunar spinel where skyrmions have only been reported very recently. It belongs to the AM₄X₈ family, where A is a post-transition metal, M is a transition metal and X is a chalcogenide, whose most celebrated member is GaV₄S₈, a compound where the existence of skyrmions has been firmly established. In this work, we obtained pure amounts of polycrystalline GaMo₄S₈ through a new synthetic route, a solid-state reaction between MoS₂ and Ga, at high temperature (1000 °C). Composition and purity were confirmed through the Rietveld refinement of the powder XRD pattern, where no additional phases were found. The magnetic phase diagram was investigated using DC (VSM) and AC magnetometry, affording novel insights into the physical properties of GaMo₄S₈. In addition to the skyrmionic phase present below T_C for applied magnetic fields between 5 kOe and 15 kOe, we have found evidence for the presence of a cluster spin-glass phase (T_g = 15.3 K), observed under small applied magnetic fields. An additional anomaly at 5 K, detected in AC susceptibility measurements, correlates with an anomalous behaviour of the magnetic field dependence of the specific heat at low temperature.