Charge Disproportionation and Magnetoresistivity in a Double Perovskite with Alternate Fe⁴⁺(d⁴) and Mn⁴⁺(d³) Layers

Abstract

Abstract An oxygen‐stoichiometric, B‐site‐ordered perovskite Ca 2 Fe 1.1 Mn 0.9 O 6 (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 KClO 4 . The structure crystallizes in the P 2 1 / m space group with a doubling of the cell along all three crystallographic axes. Mössbauer spectroscopy, susceptibility, and resistivity measurements suggest ferromagnetic interactions between Fe 4+ (d 4 ) and Mn 4+ (d 3 ) along [001] through a double‐exchange mechanism, a situation similar to half‐doped manganese perovskite oxides. Upon cooling, CFMO exhibits a ferrimagnetic transition below T c = 90 K, likely accompanied by a charge disproportionation of the iron site, 2Fe 4+ → Fe 3+ + Fe 5+ . A reasonably good magnetoresistivity of 27 % was observed below T c .