Emergence of 90$^\circ$ Domain Walls in Multiferroic BiFeO$_3$ Thin Film

Multiferroics have been a fascinating area for condensed materials research since these materials offer the exciting potential applications that taking advantages of multiple orders. Multiferroic BiFeO$_3$ (BFO) has played a key role in rejuvenating the field after a report of large ferroelectric polarization. Inside this material, domain walls (DWs) of BFO are of great interests. In recent study, room-temperature conductivity at ferroelectric DWs has been observed. In this work, through epitaxial strain, BFO thin films are grown on NdScO$_3$, which provide tensile strain on BFO films, and thus results in orthorhombic-like phase and corresponding periodic 90$^\circ$ DWs. X-ray reciprocal mapping and piezoresponse force microscopy has confirmed the orthorhombic-like and 90$^\circ$ DW structure. The transport behaviors of these natural formed 90$^\circ$ DWs as a function of temperatures and magnetic fields have been probed to understand their fundamental properties. In addition, exchange bias studies and X-ray magnetic dichroism spectromicroscopy have further revealed the magnetic properties in these DWs. Our results show that 90$^\circ$ DW in orthorhombic-like BFO possesses unusual electronic and magnetic behaviors, which are different from that in bulk and might be used for modern electronic devices and nanoelectronic.