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

TL;DR

This study provides direct magnetic domain imaging evidence of a spin reorientation transition below 150 K in a ferromagnetic BiFeO$_3$ thin film, influenced by epitaxial strain, supported by both experimental and theoretical analyses.

Contribution

It presents the first direct imaging evidence of a spin reorientation transition in ferromagnetic BiFeO$_3$ thin films and links it to epitaxial strain effects supported by first-principles calculations.

Findings

Magnetic domains rotate nearly 90° across 150 K.

Transition corroborated by magnetization measurements.

Epitaxial strain induces magnetic phase change from G- to C-type.

Abstract

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$_3$.