Orbital fluctuations and orbital order in FeCr2S4

Heat-capacity investigations on the ferrimagnetic spinel FeCr2S4 poly- and single crystals provide experimental evidence of orbital liquid and orbital glass states. The low-temperature transition in the polycrystals at 10 K arises from orbital order and is very sensitive to the sample stoichiometry. In the single crystals the orbital order is fully suppressed resulting in an orbital glass state with the heat capacity following a strict T2 dependence towards zero temperature. At elevated temperatures, FeCr2S4 exhibits an unexpected large linear term of about 100 mJ mol−1 K−2 as the fingerprint of the orbital liquid.