Spin re-orientation in FeCr2S4

The spinel FeCr2S4 has been studied intensely for its peculiar magnetic and local structural changes which are sensitively influenced by the Jahn-Teller properties of Fe2+ in tetrahedral sulfur coordination. Recent muon spin rotation data give strong evidence that the commonly assumed collinear magnetic structure of this compound is only found between the Curie temperature T-C = 165 K and 50 K. For lower temperatures a helical structure has been proposed. We present new Mossbauer spectroscopic data taken on the same sample as used for muon spin rotation. Also the hyperfine spectra revealing non-equivalent iron sites support the appearance of a spin re-orientation around 50 K which may be related to the onset of short-range orbital order. Below 20 K severe dynamic broadenings are found which may indicate orbital fluctuations. Orbital order occurs around 11 K accompanied by severe changes in the crystalline electric field ground state as traced from quadrupole interaction.