Structure, magnetic susceptibility, and specific heat of the spin-orbital-liquid candidate FeSc2S4 : Influence of Fe off-stoichiometry

Abstract

We report structural, susceptibility and specific heat studies of stoichiometric and offstoichiometric poly-and single crystals of the A-site spinel compound FeSc 2 S 4 . In stoichiometric samples no long-range magnetic order is found down to 1.8 K. The magnetic susceptibility of these samples is field independent in the temperature range 10 -400 K and does not show irreversible effects at low temperatures. In contrast, the magnetic susceptibility of samples with iron excess shows substantial field dependence at high temperatures and manifests a pronounced magnetic irreversibility at low temperatures with a difference between ZFC and FC susceptibilities and a maximum at 10 K reminiscent of a magnetic transition. Single crystal x-ray diffraction of the stoichiometric samples revealed a single phase spinel structure without site inversion. In single crystalline samples with Fe excess besides the main spinel phase a second ordered single-crystal phase was detected with the diffraction pattern of a vacancy-ordered superstructure of iron sulfide, close to the 5C polytype Fe 9 S 10 . Specific heat studies reveal a broad anomaly, which evolves below 20 K in both stoichiometric and off-stoichiometric crystals. We show that the low-temperature specific heat can be well described by considering the low-lying spin-orbital electronic levels of Fe 2+ions. Our results demonstrate significant influence of excess Fe ions on intrinsic magnetic behavior of FeSc 2 S 4 and provide support for the spin-orbital liquid scenario proposed in earlier studies for the stoichiometric compound.

Seeded Chemical Vapor Transport Growth of Cu2OSeO3

“…The techniques and chemical insight reported herein are applicable to numerous electronically and magnetically interesting systems currently grown by traditional, unseeded CVT, such as Weyl semimetals WTe 2 , MoTe 2 , ZrTe 5 , TaP, NbP, superconductor FeSe, and spin-liquid candidate FeSc 2 S 4 . [31][32][33][34][35][36]…”

Realizing square and diamond lattice S=1/2 Heisenberg antiferromagnet models in the α and β phases of the coordination framework, Abdeldaim1, Li2, Farrar3 et al. 2020Phys. Rev. Materials

“…Signatures of this dynamic behavior have been observed in material realizations of the J 1 -J 2 FDL model, such as in MnSc 2 S 4 [24] and CoAl 2 O 4 [26], where theory combined with experimental diffuse neutron scattering studies conclude the presence of a continuous spin-spiral surface in momentum space [23,24]. Perturbations further enrich the magnetism of such FDL systems, and spin-orbit coupling [27][28][29], further-neighbor couplings, and structural distortions [22] can play a significant role in determining the magnetic ground state.…”

Frustrated Magnetism in Fluoride and Chalcogenide Pyrochlore Lattice Materials

“…These materials have either surprisingly low [80], or no observed [80][81][82][83] magnetic ordering transitions down to liquid helium temperatures, pointing to the importance of geometric frustration. In fact, of the chalcogenides spinels with magnetic ions on both sites, it is only those with significant site mixing and disorder that have been observed to magnetically order [84][85][86]. The nature of the magnetic frustration in this family is still poorly understood and explored, and the fact that there is a magnetic atom on the A-site as well adds an entirely new layer of complexity that is beyond the scope of pyrochlore-lattice frustration.…”