Magnetic properties in spinel Fe1+xCr2-xS4 with CMR effect

The spinel compounds Fe1+xCr2-xS4 (x = 0, 0.1) with CMR effects but without Jahn-Taller ions are investigated. Mossbauer spectra identify that, in the FeCr2S4, Fe ions occupy tetrahedral sites in the Fe2+ valence state forming an Fe sub-lattice, the Cr ions occupy octahedral sites with a +3 valence forming an Cr sub-lattice; in Fe1.1Cr1.9S4, the excessive Fe ions substitute for Cr ions in the +3 valence. ESR measurements show that only one ESR signal, with a g-factor near 2, appears at temperatures above T-c (the PM state) for each sample; at T < T-1 (T-1 corresponding to the minimum resistivity in the rho-T curve below T-c), the original PM peak in the ESR spectra splits into a high-field ESR peak and a lower-field ESR peak. Therefore, the micromagnetism in this system can be illustrated as below: for FeCr2S4, the spins of the Fe and Cr sub-lattices both enter ferromagnetic states. At the same time, the magnetic moments of these two sub-lattices are anti-parallel to each other; for Fe1.1Cr1.9S4, the spins of the excess Fe ions are anti-parallel to those of the Cr ions, a fact which weakens not only the internal field of the Cr sub-lattice but also the coupling between these two sub-lattices. From this, the abnormal transport behavior revealed by rho-T curves for Fe1+xCr2-xS4 can be well explained. (C) 2000 Elsevier Science Ltd. All rights reserved.