Establishing magneto-structural relationships in the solid solutions of the skyrmion hosting family of materials: GaV4S8−ySey

Abstract

The GaV4S8−ySey (y = 0 to 8) family of materials have been synthesized in both polycrystalline and single crystal form, and their structural and magnetic properties thoroughly investigated. Each of these materials crystallizes in the F$$\bar{4}$$ 4 ˉ 3m space group at ambient temperature. However, in contrast to the end members GaV4S8 and GaV4Se8, that undergo a structural transition to the R3m space group at 42 and 41 K respectively, the solid solutions (y = 1 to 7) retain cubic symmetry down to 1.5 K. In zero applied field the end members of the family order ferromagnetically at 13 K (GaV4S8) and 18 K (GaV4Se8), while the intermediate compounds exhibit a spin-glass-like ground state. We demonstrate that the magnetic structure of GaV4S8 shows localization of spins on the V cations, indicating that a charge ordering mechanism drives the structural phase transition. We conclude that the observation of both structural and ferromagnetic transitions in the end members of the series in zero field is a prerequisite for the stabilization of a skyrmion phase, and discuss how the absence of these transitions in the y = 1 to 7 materials can be explained by their structural properties.

Magnetism and Néel skyrmion dynamics in GaV4S8−ySey

“…In conclusion, our results show that magnetic order is preserved for low levels of substitution in GaV 4 S 8−y Se y at both ends of the series in contrast to higher levels where spin glasslike behavior is observed [21,22]. On the Se-rich end of the series, the presence of S simply leads to an increase in the width of the local magnetic-field distribution, which is enough to prevent observation of the effect of the SkL in our TF measurements.…”

“…Polycrystalline samples of GaV 4 S 8−y Se y were synthesized and characterized as described in Refs. [21,22]. Whereas polycrystalline samples are likely to exhibit a different magnetic phase diagram to those of single crystals (whose behavior varies depending on the alignment between applied field and crystallographic axes), we have previously shown that the SkL can be identified unambiguously [21].…”

“…2(a)-2(c). Simulations of the magnetic field [31,32] at the muon-stopping sites [21] for the ground-state magnetic structures proposed for GaV 4 S 8 [17,22,33] show that the distribution most closely resembles the ferromagneticlike (FM*) state [ Fig. 3(a)] at low temperatures, and the incommensurate cycloidal (C) state at higher temperatures.…”

Structure and magnetism of the skyrmion hosting family GaV4S8−ySey with low levels of substitutions between Holt1, Štefančič2, Ritter3 et al. 2020Phys. Rev. Materials5050View full textAdd to dashboardCite

“…‡ G.Balakrishnan@warwick.ac.uk have been extensively studied as skyrmion hosts [2,3,6,24]. Both GaV 4 S 8 and GaV 4 Se 8 are isostructural with a structural phase transition from a high-temperature cubic F43m phase to a low-temperature rhombohedral R3m structure at 42 and 43 K, respectively, with a further magnetic transition at 13 and 18 K, respectively [17,23].…”

“…In this structure, there are two distinct sites on which the chalcogenides can sit: either the S1/Se1 site within the V 4 X 4 cluster or the S2/Se2 site within the GaX 4 tetrahedra. It has been suggested that the cubic-to-rhombohedral phase transition is driven by such mechanisms as a cooperative Jahn-Teller distortion [25] and charge order of the V 4 cluster formed of three V 3+ and one V 4+ ion [24]. In the low-temperature rhombohedral phase a single V ion distorts along the one of the four possible cubic 111 directions in the V 4 X 4 cluster.…”