Polar and magnetic order in GaV4Se8

Abstract

In the present work, we provide results from specific heat, magnetic susceptibility, dielectric constant, ac conductivity, and electrical polarization measurements performed on the lacunar spinel GaV 4 Se 8 . With decreasing temperature, we observe a transition from the paraelectric and paramagnetic cubic state into a polar, probably ferroelectric state at 42 K followed by magnetic ordering at 18 K. The polar transition is likely driven by the Jahn-Teller effect due to the degeneracy of the V 4 cluster orbitals. The excess polarization arising in the magnetic phase indicates considerable magnetoelectric coupling. Overall, the behavior of GaV 4 Se 8 in many respects is similar to that of the skyrmion host GaV 4 S 8 , exhibiting a complex interplay of orbital, spin, lattice, and polar degrees of freedom. However, its dielectric behavior at the polar transition markedly differs from that of the Jahn-Teller-driven ferroelectric GeV 4 S 8 , which can be ascribed to the dissimilar electronic structure of the Ge compound.

Macroscopic manifestation of domain-wall magnetism and magnetoelectric effect in a Néel-type skyrmion host

“…Lacunar spinels with the chemical formula AB 4 X 8 (A = Al, Ga, Ge; B = V, Mo, Nb, Ta; X = S, Se, Te) are a family of narrow-gap Mott insulators 31,32 , exhibiting a plethora of correlation and spin-orbit effects, including pressure-induced superconductivity 33 , bandwidth-controlled metal-to-insulator transition 34 , electric-field-driven avalanche of the Mott gap 35 , large negative magnetoresistance 36 , twodimensional topological insulator state 37 and orbitally driven ferroelectricity [38][39][40][41] . In addition to these charge related phenomena and particularly important for the present study, lacunar spinels, such as GaV 4 S 8 , GaV 4 Se 8 and GaMo 4 S 8 , were the first material family found to host the Néel-type skyrmion lattice (SkL) state [42][43][44] .…”

Magnetoentropic mapping and computational modeling of cycloids and skyrmions in the lacunar spinels GaV4S8 and GaV4Se8Zuo1, Kitchaev2, Schueller3 et al. 2021Phys. Rev. Materials5010View full textAdd to dashboardCite

“…In all cases, cycloidal propagation vectors lie in the plane perpendicular to the 111 direction of the high-T cubic structure shown in Figure 1 (equivalently, perpendicular to the 001 direction in the low-T R3m phase). This behavior, including the emergence of Néel skyrmion lattices, has been demonstrated in GaV 4 S 8 [11,24,25], GaV 4 Se 8 [10,[26][27][28], FIG. 1.…”

“…where M s is the saturation magnetization [18]. For GaV 4 S 8 and GaV 4 Se 8 , the approximate parametrization of this Hamiltonian is given by q = 1/26 [11] and q = 1/27 [26], J = 1.4 meV and J = 2.0 meV, K * = −1.0 and K * = 0.33 respectively, based on a comparison of the experimental phase diagrams shown in Figure 5 and Monte Carlo results elaborated below.…”

Spin dynamics in the skyrmion-host lacunar spinel GaV4S8

“…GaV 4 S 8 belongs to the lacunar spinel family of compounds with a chemical formula AM 4 X 8 (A = Ga, Ge; M = V, Mo, Nb, and Ta; X = S and Se) [20][21][22][23][24][25][26][27][28][29][30][31], where the magnetic M ions form a breathing pyrochlore lattice as shown in Fig. 1(a).…”