Charge disproportionation and magnetoresistivity in a double perovskite with alternate Fe4+(d4) and Mn4+(d3) layers

Abstract

An oxygen-stoichiometric, B-site-ordered perovskite Ca2Fe1.1Mn0.9O6 (CFMO) with alternate stacking of Fe and Mn layers was obtained through topochemical oxidation of the corresponding brownmillerite phase under high pressure in the presence of KClO4. The structure crystallizes in the P21/m space group with a doubling of the cell along all three crystallographic axes. Mössbauer spectroscopy, susceptibility, and resistivity measurements suggest ferromagnetic interactions between Fe4+(d4) and Mn4+(d3) along [001] through a double-exchange mechanism, a situation similar to half-doped manganese perovskite oxides. Upon cooling, CFMO exhibits a ferrimagnetic transition below Tc = 90K, likely accompanied by a charge disproportionation of the iron site, 2Fe4+ Fe3+ + Fe5+. A reasonably good magnetoresistivity of 27% was observed below Tc.