Complex magnetic, electrical and magnetoresistance properties of the coexisting Mn–Fe order–disorder phase derived from nanocomposite perovskite oxides

Abstract

We present a conceptually original study on temperature-controlled interfacial reactions in the La_0.45Ca_0.55MnO₃–LaFeO₃ nanocomposite. It highlights that the topotactic interfacial reactions can be utilized as an innovative and broader strategy for functional oxide design through the temperature controlled tuning of cation ordering. It provides the opportunity to rule out the charge and size limitation to attain the cation ordering phenomenon. Consequently, the cation ordering and associated magnetic properties can be customized through regulation of the reaction temperature. Unusual ordering of Mn and Fe has been achieved in ceramic samples through the interfacial topotactic reaction between La_0.45Ca_0.55MnO₃ and LaFeO₃ (LCMO–LFO) in the nanocomposite form. The ordering of Mn and Fe has been manifested in artificial superlattices of 1 : 1 LaMnO₃–LaFeO₃. The LCMO–LFO composite annealed at 700 and 800 °C exhibits ordering of Mn and Fe with a ferromagnetic T_C of 225 K in corroboration with the T_C of 230 K in the LaMnO₃–LaFeO₃ superlattice. The complete randomization of Mn and Fe in the 1000 °C annealed LCMO–LFO composite revealed the lack of long range magnetic ordering, whereas the 900 °C annealed LCMO–LFO nanocomposite has evidenced spectacular evolution of complex magnetic and electrical states having amalgamated features of the low temperature ordered state and the high temperature disorder phase. The coexisting order–disorder phases in the 900 °C annealed LCMO–LFO nanocomposite exhibit the emergence of the Griffiths phase, negative magnetoresistance and preferred Mott variable range hopping type electrical conduction at high temperature. On the other hand, a tendency towards long-range ferromagnetic cluster formation and the magnetic glassy state appear at lower temperatures. This partially ordered Mn–Fe based perovskite establishes a bridge between the ordered and disordered phases. This study unravels a potential deliberate route to design cation order/disorder functional ceramic materials through a temperature controlled interfacial topotactic reaction in the nanocomposite by overruling the differential charge and size limitation to achieve cation ordering.