Impact of Samarium on the Growth of Epitaxial Bismuth Ferrite Thin Films

Doping of rhombohedral bismuth ferrite (BFO) with rare earth elements has been widely investigated as a pathway to extract ferromagnetic response from an otherwise antiferromagnetic material. However, increased level of such doping, in conjunction with the ability of BFO to accommodate large strain, has also resulted in nontrivial changes in the structure, i.e., transition to orthorhombic structure and phase separation to form vertically aligned columns. Herein, epitaxially grown and single crystalline samarium oxide (Sm2O3) and doped BFO films are used to investigate the structural evolution. Thin films are grown from undoped (BFO and Sm2O3) and doped targets, (0.2,0.5)Sm2O3-(0.8,0.5)BFO. In addition, the in-plane strain, imposed by the lattice mismatch between film and substrates, is used to demonstrate the stability of the structures formed in the doped films. Interestingly, the resultant orthorhombic structures are found to be largely independent of the underlying substrates. In-depth structural and nanoscopic measurements are conducted to investigate the structures. Ordered columnar structures, reminiscent of phase separation, are successfully obtained albeit driven by spontaneous ordering of differently oriented crystals.