Ferroelectric and Magnetic Properties of Hexagonal ErFeO₃ Epitaxial Films

Hexagonal rare-earth iron oxides (h-RFeO3) exhibit both magnetic and ferroelectric orders. The ferroic properties depend on the R ionic radius; for example, they are antiferroelectric (AFE) when R = Dy and ferroelectric (FE) when R = Tm, Yb, and Lu. However, insights into the ferroelectric properties of h-ErFeO3, characterized by an intermediate ionic radius, are hampered by its severe electric leakage current. In this study, we successfully prepared h-ErFeO3 films with limited electric leakage current via atomically flat indium tin oxide bottom electrodes. The electric insulation enhancement allowed us to investigate the ferroelectric properties of the h-ErFeO3 films. The h-ErFeO3 films exhibited AFE behavior when the applied maximum electric field (Emax) was below 1 MV/cm. Conversely, clear FE polarization reversal appeared for Emax > 1 MV/cm. At Emax = 1.4 MV/cm, the remnant polarization and coercive electric field (Ec) values of the film were 2.1 μC/cm2 and 0.15 MV/cm, respectively. The Ec value of the h-ErFeO3 film was smaller than that of the other h-RFeO3 films due to its larger a-axis length. In addition, the antiferromagnetic-to-weak ferromagnetic phase transition was observed by changing the temperature. Thus, uniquely, the h-ErFeO3 film exhibited four types of ferroic properties: antiferroelectric, ferroelectric, antiferromagnetic, and weak ferromagnetic.