Magnetic order in FeCr2S4-type chalcogenide spinels

The thiospinels of composition FeCr2S4 and Fe1+xCr2-2xSnxS4 with 0 < x < 0.1 have been examined by means of extended x- ray absorption fine structure, Mossbauer spectroscopy and magnetoresistance techniques. The structural characterization shows that tin enters the spinel- related lattice as Sn4+ and occupies the octahedral B site. Appreciable magnetoresistance is observed in the temperature range 160 - 185 K which includes the magnetic ordering temperature. The effect of slight non- stoichiometry in FeCr2S4 and of tin doping is observed in the M r ossbauer spectra which show the Fe2+ ions to occupy the tetrahedral A sites. The M r ossbauer spectra recorded around the magnetic ordering temperature are sensitive to small ( 0.03 T) applied magnetic fields. The influence of tin on the low temperature magnetic behaviour is associated with the distribution of Cr3+, Sn4+ and Fe3+ ions around tetrahedral Fe2+ sites and vacancies in the anionic sublattice. An interpretation of the colossal magnetoresistance phenomena below TN is suggested.