Achieving clear ferroelectric polarization reversal in room-temperature multiferroic ε-Fe2O3 system through grain boundary engineering

Abstract

ε-Fe2O3-related oxides are promising room-temperature multiferroic materials owing to their significant magnetization and switchable ferroelectric polarization. However, their large leakage current hinders the quality of ferroelectric polarization reversal, limiting research despite superior magnetic properties compared to the well-studied BiFeO3 system. This study addresses these limitations through two investigations. First, we investigate the difficulty of polarization reversal by analyzing grain boundary structures in ε-Fe2O3-related epitaxial films, which inherently form due to their non-perovskite orthorhombic structure. Second, we enhance polarization reversal via grain boundary engineering. Our findings reveal that these films contain numerous small grains (250–770 nm2) with Fe2+/3+ states at grain boundaries, where approximately 40% act as ferroelectric domain walls. The high grain boundary density causes significant leakage current and hinders polarization reversal. By implementing a codoping method, we successfully reduce grain boundary density, achieving clear ferroelectric hysteresis with minimal leakage current. This breakthrough highlights the potential of ε-Fe2O3-related oxides as room-temperature multiferroic materials with substantial magnetization and offers new prospects for research on materials distinct from the BiFeO3 system.