Role of oxygen vacancies in deciding the high temperature magnetic properties of Ba and Sm substituted BiFeO₃ ceramics

A series of Bi_1−xA_xFeO₃ (A = Ba²⁺, Sm³⁺) compounds have been synthesized in order to reveal the influence of oxygen vacancies on the magnetic behavior of BiFeO₃. While the rhombohedral structure is retained for all compositions (0 ≤ x ≤ 0.2), the Ba²⁺ and Sm³⁺ substitution induces different structural disorder, leading to an enhancement in magnetization. Temperature dependence of magnetization between 300 K and 900 K indicates that the increased oxygen vacancy due to Ba²⁺ substitution gradually turns the original antiferromagnetic behavior of BiFeO₃ into a ferromagnetic one. In contrast, the antiferromagnetic nature of BiFeO₃ is maintained in the whole Sm³⁺ substitution range, in which the concentration of oxygen vacancies is preserved. This result reveals unambiguously that the oxygen vacancies also play a crucial role in deciding the magnetic behavior of BiFeO₃. The intrinsic magnetic property of BiFeO₃ is originated from not only the Fe³⁺/Fe³⁺ but also the unbalanced Fe³⁺/Fe²⁺ antiferromagnetic superexchange interactions. - Highlights: • The Ba/Sm-substitution induces structural distortion in BiFeO₃ (BFO). • The Ba-substitution increases the concentration of oxygen vacancies. • The increased oxygen vacancies alter the magnetic structure of BFO (AFM –FM). • The oxygen vacancies play a crucial role in deciding the magnetic behavior of BFO. • The general spin structure of BFO should be the coexistence of AFM and FM.