Manifestation of dissimilar types of magnetism in iron- and chromium-substituted Mn2SnS4

Abstract

Mn₂SnS₄ belongs to the M^II₂A^IVQ₄ (M = transition metal; A = Si, Ge and Sn; Q = S, Se and Te) class of compounds that crystallizes in the orthorhombic space group Cmmm and shows complex magnetic properties. Here we report the synthesis and magnetic properties of Fe- and Cr-substituted Mn₂SnS₄ quaternary chalcogenides. All these compounds have been synthesized using a high-temperature solid-state route. Room temperature neutron diffraction studies on the specific compositions of chromium- and iron-substituted compounds were performed to obtain the site occupancy of different elements in the unit cell. The neutron diffraction analysis by employing the Rietveld refinement shows that for the Fe-substituted compound, most of the Fe goes to the Mn site with a small amount at the Sn site, while in the Cr-substituted sample, all the Cr occupy the Mn site. However, the Sn site almost remains intact in the case of the Fe-substituted compound, while it is significantly disordered for the Cr-substituted sample as a fraction of Mn occupies the Sn site and an equivalent amount of Sn occupies the Mn site. XPS study shows that both Cr and Fe exist in the +3 oxidation state, while Mn exists in the +2 state and Sn exists in a mixture of +2 and +4 oxidation states. Magnetic property study of these substituted compounds shows different types of magnetism, which is attributed to the variation of d-electrons of the substituent atom. The chromium-doped compounds show ferrimagnetic character along with two transitions: one transition at ∼37 K and another at ∼152 K. However, in Fe-substituted Mn₂SnS₄ samples, the low-temperature transition disappears and an increase in the high-temperature antiferromagnetic ordering temperature i.e. from 152 K (Mn₂SnS₄) to 174 K (Mn_1.82Fe_0.18SnS₄) is observed. The increase in the antiferromagnetic ordering temperature in Mn_2−xFe_xSnS₄ may be attributed to the increase in the covalence of Mn/Fe–S–Mn/Fe bonds (shorter) with iron substitution.