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

• 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.

A series of Bi1−xAxFeO3 (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.