Magnetic properties of transition-metal-codoped BaTiO3 systems

Ba(Ti0.65M0.05Fe0.3)O3 (M = Cr, Mn and Ni) ceramics were prepared by solid-state reaction, and post-annealed in vacuum and oxygen, respectively. Mössbauer spectroscopy was used to investigate the local environments of Fe atoms. Combined with the configuration of the other transition metal M, the mechanisms responsible for magnetism were discussed for different samples. The results show that all samples are single-phase with a 6H–BaTiO3-type hexagonal perovskite structure. The as-prepared ceramics are all paramagnetic, while the annealed ones are all ferromagnetic at room temperature. The origin of ferromagnetism changes with doping element and annealing atmosphere, including the double-exchange mechanism of transition metal M with mixed valences, the super-exchange mechanism of Fe3+ in different occupational sites, and the super-exchange mechanism of Fe4+–O2−–Fe4+.