Growth and ferroelectric properties of Al substituted BiFeO3 epitaxial thin films

Epitaxial films of BiAlxFe1−xO3 (xBAFO) were grown on SrTiO3 (STO) and SrRuO3 buffered STO substrates using pulsed laser deposition. To understand the effects of Al substitution at the Fe-site of BFO, we systematically investigated its impact on the material’s crystal structure, surface morphology, ferroelectric properties, and magnetic properties. Our x-ray diffraction analysis revealed that phase-pure xBAFO films can be stabilized for Al concentrations between 0% and 35%, without the formation of secondary phases, due to the isotypic crystal structures of BiAlO3 and BiFeO3. This allowed the rhombohedral structure of BAFO to be preserved. We then characterized the ferroelectric properties of xBAFO (0≤x≤0.25 ) by analyzing polarization-voltage hysteresis loops, which exhibited a transition from a nearly square shape to a more slanted shape with increasing Al substitution. Additionally, piezoresponse force microscopy revealed that the domain growth mode, shape, size, dimension, and nucleation play a crucial role in the switching behavior of ferroelectric materials. Furthermore, we observed a modest enhancement in magnetization due to the modified spin ordering of Fe atoms with Al substitution. Notably, the optimal ferroelectric and magnetic properties were achieved at an Al concentration of 15%. These findings suggest that BAFO is a promising magnetoelectric material with desired functionalities for realizing BFO-based next-generation non-volatile memory devices.