Entanglement of cation ordering and manipulation of the magnetic properties through a temperature-controlled topotactic interface reaction in nanocomposite perovskite oxides

Abstract

Achievement of B-site cation ordering for LaFe_0.5Mn_0.5O₃, unlike other LaB_0.5B′_0.5O₃ perovskites, has not been reported yet in polycrystalline samples. Thus far, there has been only one report on Fe and Mn ordering in LaMnO₃–LaFeO₃ artificial superlattices constructed on SrTiO₃ using laser MBE methods [Ueda et al. Phys. Rev. B, 1999, 60, R12561.]. The ferromagnetic ordering with the T_C around 230 K has been attributed to the Fe³⁺(d⁵)–O–Mn³⁺(d⁴) superexchange interaction for the superlattice with 1/1 stacking periodicity. Here, for the first time, we report the Fe and Mn ordering at the interface of the La_0.45Ca_0.55MnO₃–LaFeO₃ (LCMO–LFO) nanocomposite, achieving a T_C of ∼225 K. It has been also observed that such an ordering is very sensitive to the processing temperature. Processing the composite at 1000 °C leads to complete randomization in the cationic distribution, which results in suppression of the high temperature transition at 225 K observed for 700 and 800 °C heat-treated samples. High-resolution TEM, HAADF, EDX mapping and ED analysis support the interfacial phase formation. This cationic ordering through interfacial reaction is further substantiated by the formation of a well-studied La₂MnCoO₆ double perovskite obtained from a LaMnO₃–LaCoO₃ nanocomposite by thermal treatment under similar conditions as that of the LCMO–LFO system. Our study revealed that by means of the interface reaction during composite processing, the product phase may dominate the overall property of the system. The temperature-controlled cationic ordering at the interfacial product phase of dominating magnetic properties may provide a novel route to design functional ceramic materials.