Fe2−xCuxSnS4: Synthesis, structure and magnetic properties of a series of disordered spinels

Abstract

Quaternary chalcogenides of compositions Fe2−xCuxSnS4 (x = 0.3, 0.4, 0.5, 0.6, 0.7) were synthesized at high temperature, 800 °C, in a sealed silica tube. All the compounds crystallized in the spinel structure type with cubic Fd−3 m space group. Both magnetic and nonmagnetic ions are disordered in these compounds with Fe/Sn occupies half of the octahedral voids while Fe/Cu occupies 1/8th of the tetrahedral voids as obtained from the Rietveld refinement of powder X-ray diffraction data. XPS study indicates that Fe exists in both +2 and + 3 oxidation states while Cu, Sn and S adopt +1, +4 and −2 oxidation states, respectively. Magnetic susceptibility study suggests ferrimagnetic like ordering in Fe1.6Cu0.4SnS4 below 230 K and the ordering temperature gradually decreases from 230 K to about 120 K with increase in Cu substitution. As the amount of Cu(I) increases in Fe2−xCuxSnS4, the percentage of Fe(III) increases to balance the charge. The magnetocaloric properties of polycrystalline Fe1.6Cu0.4SnS4 has been studied for their potential applications as magnetic refrigerant at cryogenic temperatures. With an applied magnetic field of 5 T, the maximum value of magnetic entropy change was found to be (Δ Sm) 0.4 Jkg−1K−1 with a relative cooling power (RCP) of 7 J kg−1. These values are very similar to the literature reported values for Fe based compounds. Further, manipulation at the Fe site may lead to enhancement of magnetocaloric effect for practical applications.