Preparation of monoclinic 0.9(BiFeO₃)-0.1(BiCoO₃) epitaxial films on orthorhombic YAlO₃ (100) substrates by r.f. magnetron sputtering

0.9BiFeO₃-0.1BiCoO₃ (BFCO) films (t=100 nm) were prepared on orthorhombic YAlO₃ (YAO) (100) substrates by r.f. magnetron sputtering. Film flatness, crystallinity, crystal symmetry, and secondary phase formation are strongly affected by the pressure of the sputtering gasses, Ar and O₂. Phi-scan measurements showed that the films were epitaxially grown on the substrates, with the crystal relation [101]_p(101)_p BFCO||[101]_p(101)_p YAO. X-ray reciprocal space mapping revealed that the crystal symmetry of the BFCO films was a pseudo-cubic-like monoclinic structure, with M_C phase, rather than the Cm symmetry of the bulk BFCO. Cross-sectional transmission electron microscopy analysis revealed that the film had, as a result of a lattice misfit of 7%, strong compressive strain less than 10 nm from the interface, which relaxed monotonically with increasing distance from the interface. Magnetic measurements show that strained monoclinic BFCO has smaller magnetization compared to rhombohedral BFCO.