Evidence of spin reorientation transition below 150 K from magnetic force microscopy in a ferromagnetic BiFeO\(_3\) thin film

We investigated the magnetic transitions in BiFeO\(_3\) at low temperature (5-300 K) and observed nearly 90\(^o\) rotation of magnetic domains (imaged by vertical magnetic force microscopy) across 150 K in an epitaxial thin film of thickness \(\sim\)36 nm. It offers a clear evidence of spin reorientation transition. It also corroborates the transition observed below \(\sim\)150 K in the zero-field-cooled and field-cooled magnetization versus temperature data. The field-driven 180\(^o\) domain switching at room temperature, on the other hand, signifies presence of ferromagnetism. Since bulk antiferromagnetic BiFeO\(_3\) does not exhibit such a transition, this observation in ferromagnetic thin film of BiFeO\(_3\) indicates a radical effect because of epitaxial strain. Density functional theory based first-principles calculations too reveal that combined in- and out-of-plane epitaxial strain induces magnetic transition from G- to C-type structure in BiFeO\(_3\).