Probing the role of cation vacancies on the ferromagnetism of La-doped BiFeO3 ceramics

Single-phase multiferroic Bi1−xLaxFeO3 (x = 0.00, 0.10, 0.20, 0.30, and 0.40) ceramics were studied by positron annihilation lifetime spectroscopy and the effect of the cation vacancies on the magnetism were investigated. Positron lifetime measurements and density-functional theory calculation of positron lifetimes identified the presence of Bi and Fe vacancies. It was observed that when x > 0.20 the Bi monovacancies disappeared gradually and some larger vacancy clusters begin to appear. Magnetic property measurements showed that the remnant magnetization increases greatly when x > 0.20. It is found that the enhanced magnetization is not only due to the suppressed spin cycloid structure, but the variation of cation defects also contributes.