Influence of the Change in Oxidation Number of Mn on Magnetic Properties of

We prepared BaTi_1-xMn_xO₃ samples (x = 0 and 0.05) by standard solid-state reaction at 700°C and 900°C in an Ar ambient to change oxidation number of Mn dopants. The fabricated samples were then studied structural characterization and electronic structures by means of X-ray diffraction and absorption, and Raman scattering and electron-spin-resonance spectrometers. We found oxidation numbers 2+ and 3+ of Mn ions coexisting in BaTi_1-xMn_xO₃ with x = 0.05, where the Mn²⁺/Mn³⁺ ratio is about one for the sample annealed at 700°C. These Mn ions prefer locating at the Ti site in the tetragonal BaTiO₃ host lattice. In particular, there is a change in the oxidation number of Mn²⁺ → Mn³⁺ when the annealing temperature changes from 700°C to 900°C. Their magnetic properties are accordingly changed. Meanwhile, annealing pure BaTiO₃ in an Ar ambient at 700°C and 900°C does not lead to ferromagnetic (FM) order; they are almost diamagnetic. With the obtained results, we believe that FM order in Mn-doped BaTiO₃ annealed in an Ar ambient is associated with exchange interactions of Mn²⁺ ions mediated by oxygen vacancies rather than associated with Mn³⁺ ions.