Metallic conduction in high Curie temperature ferromagnetic heavy rare earth monoxides REO (RE = Tb, Dy, Er): rare-earth-dependent carrier polarity and anomalous Hall effect

Recently synthesized single-phase heavy rare earth monoxides, rocksalt type REO (RE = Tb, Dy, Er), exhibited metallic electronic states with [Xe]4fⁿ5d¹ electron configurations and high Curie temperature. Hence, the 4f–5d hybridization is expected to significantly influence the electrical transport properties. In this study, these REOs were found to show metallic conduction with gradually varied carrier polarity, where TbO was an n-type metal, DyO was a partially compensated n-type metal, and ErO was a partially compensated p-type metal. This variable carrier polarity is probably due to the degree of 4f–5d hybridization depending on each RE ion. The anomalous Hall effect possessed a larger remanence and coercive field than those of the magnetization below each Curie temperature. Intriguingly, ErO showed unusual clockwise hysteresis loops of the anomalous Hall effect with a superficially positive anomalous Hall coefficient, in contrast with usual anticlockwise hysteresis loops of the positive anomalous Hall effect in TbO and DyO. This unusual behavior of ErO is likely due to multiple anomalous Hall effects or a superposed semimetallic ordinary Hall effect. The simple rocksalt structure, strong spin–orbit interaction, and various carrier polarities as well as anomalous Hall effect would be beneficial to develop spintronic heterostructures.