Complex Transition Metal Chalcogenide Ferromagnetic Semiconductor with General Formula MSb2Se4 (M=Mn , Fe): Synthesis and Characterization.

Abstract

We report two new magnetic semiconducting compounds (FeSb2Se4 and MnSb2Se4), which are subsequently used as template for the investigation of the effect of electronic structure engineering of low band gap magnetic semiconductor in the magnetic behavior and the Curie ferromagnetic to paramagnetic transition temperature (Tc). Compounds were synthesized by solid-state reaction of the elements at moderate temperature. Both compounds crystallize in the monoclinic crystal system with space group C2/m (#12). Their crystal structure can be viewed as consisting of two types of building units, denoted A and B alternate along [001]. The unit A is built of paired rods of face-sharing monocapped trigonal prisms around Sb atoms alternating along the a-axis with a single chain of edge-sharing octahedra around the magnetic M (Fe, Mn) atoms. The unit B is a NaCl-type block separating adjacent units A, within which chains of edge-sharing octahedral around Sb atoms alternate along the a-axis with a single chain of edge-sharing octahedra around the magnetic M (Fe, Mn). Temperature dependent measurements of the magnetic susceptibility and electrical conductivity revealed that FeSb2Se4 is a high temperature p-type ferromagnetic semiconductor with an electrical conductivity of ~ 2 S/cm and the Curie transition temperature Tc ~ 450K, whereas a dominant antiferromagnetic ordering was observed in the MnSb2Se4 compound. To probe the effect of changes in the electronic transport properties in FeSb2Se4 and MnSb2Se4 on their magnetic behavior, the solid-solution series, Fe1-xSb2SnxSe4, FeSb2-xSnxSe4, MnSb2-xSnxSe4, and FeSb2Se4-xTex were investigated. All Fe containing compositions (except the FeSb2Se4-xTex series (x= 1, 2, 3 and 4) were found to be isostructural with FeSb2Se4 and showed a ferromagnetic ordering up to 600K with magnetic and electronic transitions at 130K,321K, 400K and 440K. These transitions were found also to be related to structural changes upon heating or cooling from 300K. The transitions at 130K, 400K and 440K disappear with increasing concentration of Sn indicating the structural effect is annealed with increasing Sn content. The materials exhibit large positive values of the thermopower and optical measurements revealed an optical band gap of 0.32eV, suggesting that the substituted FeSb2Se4 families of compounds are p-type narrows band gap semiconductors.