Ferrimagnetism and Ferroelectricity in Cr-Substituted GaFeO₃ Epitaxial Films

GaFeO₃-type iron oxides are promising multiferroic materials due to the coexistence of a large spontaneous magnetization and polarization near room temperature. However, magnetic substitution, which is a general method to control multiferroic properties, is difficult due to instability of the substituted GaFeO₃. In this study, Ga_0.5Cr_0.5FeO₃ epitaxial thin films are successfully fabricated through epitaxial stabilization. These films exhibit in-plane ferrimagnetism and out-of-plane ferroelectricity simultaneously. X-ray absorption spectroscopy and X-ray magnetic circular dichroism measurements of the Ga_0.5Cr_0.5FeO₃ film reveal that the oxidation states of the Fe and Cr ions are trivalent. In addition, some Fe ions are located at tetrahedral Ga1 sites. Compared to the GaFeO₃ film, the Ga_0.5Cr_0.5FeO₃ film shows a higher magnetic phase transition temperature (240 K), weaker saturation magnetization at 5 K, and a unique temperature dependence of the magnetization behavior. The effects of Cr substitution on the magnetic properties are strongly affected by the sites of the Fe³⁺ (3d⁵) and Cr³⁺ (3d³) ions. Furthermore, room-temperature ferroelectricity in the GaFeO₃ and Ga_0.5Cr_0.5FeO₃ films was demonstrated. Interestingly, the change in the ferroelectric parameters via Cr substitution is very small, which disagrees with the previously proposed polarization switching mechanism. Our findings are key to understanding the genuine polarization switching mechanism of the multiferroic GaFeO₃ system

Crystal Isomers of ScFeO₃

In inorganic compounds, “crystal isomers”, which can exist in metastable phases, are obtained by various solution-processing techniques, high-pressure syntheses, as well as physical and chemical thin film fabrication techniques. The metastable phase depends on the processing, allowing the hierarchy of the Gibbs free energy to be controlled in a phase at a given temperature. In this study, we successfully stabilize five metastable phases, four phases of ScFeO₃ and one Sc_0.48Fe_1.52O₃, prepared from one ScFeO₃ target by the pulsed laser deposition technique. The crystal structures are identified by X-ray diffraction and high-angle annular dark field-scanning transmitted electron microscopy measurements. The relationship between the crystal structure of the film and the substrate is κ-Al₂O₃-type Sc_0.48Fe_1.52O₃ on SrTiO₃(111), spinel-type ScFeO₃ on MgO(001), corundum-type ScFeO₃ on Fe₂O₃/Al₂O₃(0001) and NdCaAlO₄(001), YMnO₃-type ScFeO₃ on Al₂O₃(0001), and bixbyite-type ScFeO₃ on YSZ(001). Four of these structures (all except the bixbyite structure) have not been reported by other processing techniques. These results suggest that the thin film growth technique is a strong tool for exploring novel functional materials and the metastable phases of oxide isomers