Abstract
The spinel compounds Fe1+xCr2−xS4 (x=0, 0.1) with CMR effects but without Jahn–Taller ions are investigated. Mössbauer 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 Tc (the PM state) for each sample; at T<T1 (T1 corresponding to the minimum resistivity in the ρ–T curve below Tc), the original PM peak in the ESR spectra splits into a high-field ESR peak and a lower-field ESR peak. Therefore, the micro-magnetism 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 ρ–T curves for Fe1+xCr2−xS4 can be well explained.
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