Compositional tuning of the strain-induced structural phase transition and of ferromagnetism in Bi_1-xBa_xFeO_3-δ

Recent studies by a number of research groups have shown that the structure of epitaxial BiFeO₃ (BFO) films changes drastically as a function of substrate-induced biaxial compression, with the crystal structure changing from one being nearly rhombohedral (R-like) to one being nearly tetragonal (T-like), where the "T-like" structure is characterized by a highly enhanced c/a ratio of out-of-plane c to in-plane a lattice parameters. In this work, we show that the critical compressive strain σ_c necessary to induce this transition can be reduced significantly by substituting 10% Ba for Bi [Bi_0.9Ba_0.1FeO_3-δ (BBFO)] and that the "T-like" phase in both BBFO and BFO is stable up to the decomposition temperatures of the films in air. Furthermore, our results show that the BBFO solid solution shows clear ferromagnetic properties in contrast to its undoped BFO counterpart.