Possible emergence of a skyrmion phase in ferroelectric GaMo4S8

Abstract

Polar lacunar spinels, such as GaV4S8 and GaV4Se8, were proposed to host skyrmion phases under magnetic field. In this work, we put forward, as a candidate for Néel-type skyrmion lattice, the isostructural GaMo4S8, here systematically studied via both firstprinciples calculations and Monte Carlo simulations of model Hamiltonian. Electric polarization, driven by Jahn-Teller distortion, is predicted to arise in GaMo4S8, showing a comparable size but an opposite sign with respect to that evaluated in V-based counterparts and explained in terms of different electron counting arguments and resulting distortions. Interestingly, a larger spin-orbit coupling of 4d orbitals with respect to 3d orbitals in vanadium-spinels leads to stronger Dzyaloshinskii-Moriya interactions, which are beneficial to stabilize a cycloidal spin texture, as well as smaller-sized skyrmions (radius<10 nm). Furthermore, the possibly large exchange anisotropy of GaMo4S8 may lead to a ferroelectricferromagnetic ground state, as an alternative to the ferroelectric-skyrmionic one, calling for further experimental verification. *

Mapping skyrmion stability in uniaxial lacunar spinel magnets from first principles

“…The lacunar spinels GaM 4 X 8 are a convenient model system for studying mechanisms leading to robust skyrmion stability at all temperatures below the Curie temperature. GaV 4 S 8 [13] and GaV 4 Se 8 [10,11] have been reported as skyrmion hosts with unusually wide thermal stability windows, while GaMo 4 S 8 has been suggested as a skyrmion host on the basis of computational data [14]. Materials in this class exhibit significant metalmetal bonding [15,16], with electronic structure defined by isolated M 4 molecular units.…”

Mode Crystallography Analysis through the Structural Phase Transition and Magnetic Critical Behavior of the Lacunar Spinel GaMo4Se8

“…In a Mo 4 tetrahedron, there are 11 electrons in total. 29 Thus, there is only S = 1/2 per tetrahedron, which is much lower than expected in a localized picture. Furthermore, the moment in one Mo 4 unit interacts ferromagnetically with the moments in neighboring Mo 4 units and is better described using an itinerant electron formalism.…”

“…Currently, there is an effort to understand the magnetic phase diagrams of the lacunar spinels known to have R 3 m symmetry below the structural transition. In GaMo 4 S 8 , a Néel-type skyrmion phase has been theoretically predicted 29 but a modulated magnetic state with shorter periodicity (λ ≈ 9.8 nm) has been experimentally observed, 18 compared to that of the observed skyrmion phases in GaV 4 S 8 and GaV 4 Se 8 (λ ≈ 20 nm). This is attributed to the larger SOC in the 4d Mo compounds compared to the 3d V compounds.…”

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

“…This ferroelectic transition allows cycloidal modulations with propogation vectors in the plane perpendicular to 111 . GaMo 4 S 8 [18,29,30], and GaMo 4 Se 8 [31]. The magnetic phase boundaries of these materials have been mapped out by conventional techniques, including SANS, field-dependent magnetization, probe microscopy, and AC susceptibility [10,11,[31][32][33].…”

“…Furthermore, lacunar spinels are ferroelectric [10,11,34] and susceptible to structural phase transitions [31], meaning that skyrmion stability can be probed using electric fields and mechanical strain [32]. Finally, while the electronic structure of these materials is highly correlated and requires advanced computational methods to resolve [28,35], their microscopic magnetic behavior is well-captured using semi-classical spin models [18,30,36]. This combination of rich physics, abundant experimental data and quantitative theory establish the lacunar spinels as an ideal system for testing new methods for magnetic phase determination.…”