Effect of Sr concentration on microstructure and magnetic properties of (Ba1-xSrx)(Ti0.3Fe0.7)O3 ceramics

Fe-doped (Ba1-xSrx)TiO3 ceramics were prepared by solid-state reaction, and ferromagnetism was realized at room temperature. The microstructure and magnetism were modified by the Sr concentration control (0≤x≤75 at%) at a fixed Fe concentration, and the relevant magnetic exchange mechanism was discussed. All the samples are shown to have a single perovskite structure. When increasing the Sr concentration, the phase structure is transformed from a hexagonal perovskite into a cubic perovskite, with a monotonic decrease in lattice parameters induced by ionic size effect. The room-temperature ferromagnetism is expected to originate from the super-exchange interactions between Fe3+ on pentahedral and octahedral Ti sites mediated by the O2- ions. The increase in Sr addition modifies two main influencing factors in magnetic properties: the ratio of pentahedral to octahedral Fe3+ and the concentration of oxygen vacancies, leading to a gradually enhanced saturation magnetization. The highest value, obtained for Fe-doped (Ba0.25Sr0.75)TiO3, is an order of magnitude higher than that of the Fe-doped BaTiO3 system with similar Fe concentration and preparation conditions, which may indicate (Ba1-xSrx)TiO3 as a more suitable matrix material for multiferroic research.