Coexistence of Localized and Itinerant Electrons in the Double‐Perovskite Ba2Fe2/3Mo4/3O6

A polycrystalline Ba2Fe2/3Mo4/3O6 double‐perovskite has been prepared by decomposition of citrate precursors and subsequent thermal treatment under a reducing atmosphere. The crystal structure has been studied by combined X‐ray and neutron powder diffraction (XRPD and NPD). At room temperature, the structure is cubic (Fm3̄ m) with lattice parameter a = 8.0710(1) Å. It is unchanged between 3 and 320 K. The crystallographic formula is Ba2[Fe0.52(2)Mo0.48(2)]4a[Fe0.14(2)Mo0.86(2)]4bO5.9(2). NPD, electron spin resonance (ESR), and magnetization measurements show spontaneous magnetization below the Curie temperature (TC) = 310 K. The ESR behavior is associated with the presence of localized Fe3+ ions, whereas the transport properties (electrical conductivity and Seebeck effect) suggest the presence of highly correlated electrons in a metallic band with disorder, which can be associated with the Mo t2g electrons. The coexistence of localized and itinerant electrons leads to non‐negligible magnetoresistance properties.