Rocksalt-type PrO epitaxial thin film as a weak ferromagnetic Kondo lattice

A unique Kondo lattice praseodymium monoxide PrO was synthesized in the form of an epitaxial thin film. The rocksalt-type PrO thin films with a $4{f}^{2}5{d}^{1}$ electronic configuration showed metallic conduction with a local resistivity minimum at 7 K as a result of the Kondo effect. In contrast to the other paramagnetic praseodymium monochalcogenides, PrO showed weak ferromagnetism below 28 K, followed by a transition to a more ferromagneticlike phase around 5 K. Emergence of the weak ferromagnetism probably originated from the enhanced $4f\text{\ensuremath{-}}4f$ exchange interaction by the short Pr-Pr distance. For the ferromagneticlike phase below 5 K, magnetic hysteresis of the anomalous Hall effect was significantly larger than that of magnetization, probably due to competing magnetic ordering.