Enhanced Curie temperature near 300 K in highly crystalline GdO epitaxial thin films concomitant with an anomalous Hall effect

Abstract

Gadolinium monoxide (GdO) is a recently discovered ferromagnetic semiconductor with a much higher Curie temperature of 276 K compared with that of europium monoxide (EuO), an archetypal oxide ferromagnetic semiconductor. Despite the requirement of epitaxial stabilization to synthesize metastable GdO with an unusual valence state, the lack of a lattice-matched substrate suppresses the electrical conductivity and the anomalous Hall effect. Here, ferromagnetic rare earth monoxide GdO (111) epitaxial thin films are successfully grown on CaF₂ and yttria stabilized zirconia single crystal substrates by using a CaO (111) buffer layer. The buffer layer improves the crystallinity with a significantly reduced amount of Gd₂O₃ impurity phase, resulting in five-fold higher electron mobility compared to that of the GdO (001) epitaxial thin film without a buffer layer in the previous study. The improved electrical conduction enhances the ferromagnetic Curie temperature up to 303 K. In addition, the anomalous Hall effect is clearly observed. These results would enable the use of GdO in spintronic devices operated around room temperature.