This paper reports on the defect structures formed upon strain relaxation in pulsed laser-deposited complex oxide superlattices consisting of the ferromagnetic metal, La0.67Sr0.33MnO3, and the antiferromagnetic insulator, La0.67Sr0.33FeO3. Atomic resolution scanning transmission electron microscopy and electron energy loss spectroscopy were used to characterize the structure and chemistry of the defects. For thinner superlattices, strain relaxation occurs through the formation of 2-D stacking faults, whereas for thicker superlattices, the prolonged thermal exposure during film growth leads to the formation of nanoflowers and cracks/pinholes to reduce the overall strain energy.

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 σc necessary to induce this transition can be reduced significantly by substituting 10% Ba for Bi [Bi0.9Ba0.1FeO3−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.