Thickness-dependent magnetotransport properties of rocksalt NdO epitaxial thin films: observation of a ferromagnetic phase far above the Curie temperature

We investigated magnetotransport properties of rocksalt NdO (001) epitaxial thin films with various thicknesses. For the thickness of 45 nm, the NdO thin film behaved as a ferromagnetic metal with the Curie temperature (TC) of 19 K as was reported recently. With decreasing film thickness down to 3 nm, the resistivity increased monotonically, and the TC was reduced. Intriguingly, 9 nm-thick and 12 nm-thick films showed non-zero remanent magnetization and anomalous Hall effect far above the TC, up to 40 K, indicating the emergence of a weak ferromagnetic phase above the TC. A weak ferromagnetic phase was observed far above the TC in NdO thin film.