Ferroelectric and Magnetic Properties in Room-Temperature Multiferroic Ga_xFe_{2− x}O₃ Epitaxial Thin Films

GaFeO₃-type iron oxide is a promising room-temperature multiferroic material due to its large magnetization. To expand its usability, controlling the ferroelectric and magnetic properties is crucial. In this study, high-quality Ga_xFe_{2– x}O₃ (x = 0–1) epitaxial films are fabricated and their properties are systematically investigated. All films exhibit room-temperature out-of-plane ferroelectricity, showing that the coercive electric field (E_c) decreases monotonically with x. Additionally, the films show in-plane ferrimagnetism with a Curie temperature (T_C) >350 K at x = 0–0.6. The coercive magnetic field (H_c) decreases with x at x ≤ 0.6, but shows a constant value at x > 0.6, whereas the saturated magnetization (M_s) increases with x at x ≤ 0.6, but decreases with x at x > 0.6. X-ray magnetic circular dichroism reveals that the large magnetization at x = 0.6 is derived from Fe³⁺ (3d⁵) at octahedral sites. The controllable range of the E_c, H_c, and M_s values at room temperature (400–800 kV cm⁻¹, 1–8 kOe, and 0.2–0.6 µ_B/f.u.) is very wide and differs from those of well-known multiferroic BiFeO₃. Furthermore, the Ga_xFe_{2− x}O₃ films exhibit room-temperature magnetocapacitance effects, indicating that adjusting T_C near room temperature is useful to achieve large room-temperature magnetocapacitance behavior.