Squeezing the periodicity of Néel-type magnetic modulations by enhanced Dzyaloshinskii-Moriya interaction of 4d electrons

Abstract

In polar magnets, such as GaV4S8, GaV4Se8 and VOSe2O5, modulated magnetic phases namely the cycloidal and the Néel-type skyrmion lattice states were identified over extended temperature ranges, even down to zero Kelvin. Our combined small-angle neutron scattering and magnetization study shows the robustness of the Néel-type magnetic modulations also against magnetic fields up to 2 T in the polar GaMo4S8. In addition to the large upper critical field, enhanced spin-orbit coupling stabilize cycloidal, Néel skyrmion lattice phases with sub-10 nm periodicity and a peculiar distribution of the magnetic modulation vectors. Moreover, we detected an additional single-q state not observed in any other polar magnets. Thus, our work demonstrates that non-centrosymmetric magnets with 4d and 5d electron systems may give rise to various highly compressed modulated states.

Optical, Dielectric, and Magnetoelectric Properties of Ferroelectric and Antiferroelectric Lacunar Spinels

“…Bordacs et al [29] detected a Néel-type skyrmion lattice state in GaV 4 Se 8 , which was corroborated by Fujima et al [9] to exhibit a spininduced polarization similar to GaV 4 S 8 . [31] In case of GaMo 4 S 8 , the existence of a skyrmion lattice [35,80,84] as well as magnetoelectric coupling [79] has been proposed, but not experimentally verified yet.…”

“…For it was shown by Ruff et al [ 7 ] that all magnetic phases emerging at low temperatures, namely, a cycloidal, a Néel‐type skyrmion lattice, and a field‐polarized ferromagnetic phase, carry different spin‐induced ferroelectric polarizations, as shown in Figure 7. The other rhombohedral lacunar spinels, and , also undergo magnetic transitions at = 18 K [ 29 ] and = 20 K, [ 35 ] respectively. They were also found to exhibit complex magnetic phase diagrams.…”

“…In finite magnetic fields, the cycloidal order can be transformed to a Néel‐type skyrmion lattice (SkL) state and subsequently to a field‐polarized ferromagnetic (FM) state. [ 27,29,35 ] Importantly, the ferroelectric and the magnetic transitions are decoupled from each other, as shown in Figure 1b,c. The full list of transition temperatures is shown in Table 1 .…”

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

“…5 Only recent experimental studies disclosed the evidence of skyrmions in GaMo 4 Se 8 28,29 and in GaMo 4 S 8 . 30 Reports on GaMo 4 S 8 , both on its synthesis as well as on the characterisation of physical properties, remain scarce comparatively with the other skyrmion-hosting lacunar spinels. GaMo 4 S 8 is known to be a Mott insulator with ferromagnetic and cycloidal spin ordering below T C = 19 K. 4,30,31 The Jahn–Teller transition occurs at 47 K, reported by previous heat capacity measurements and dielectric relaxation studies.…”

“…30 Reports on GaMo 4 S 8 , both on its synthesis as well as on the characterisation of physical properties, remain scarce comparatively with the other skyrmion-hosting lacunar spinels. GaMo 4 S 8 is known to be a Mott insulator with ferromagnetic and cycloidal spin ordering below T C = 19 K. 4,30,31 The Jahn–Teller transition occurs at 47 K, reported by previous heat capacity measurements and dielectric relaxation studies. 31 Some differences in the structural distortions of GaMo 4 S 8 can be found in comparison to those reported for GaV 4 S 8 , namely the rhombohedral angle α in the distorted phase is smaller than 60° in the V compound, and larger than 60° in the Mo compound, which inverts the order of the a 1 and e orbitals resulting from the orbital splitting by the crystal field.…”