Observation of two-channel anomalous Hall effect in perpendicularly magnetized NiCo2O4 epitaxial films

The anomalous Hall effect (AHE) is essential for developing highly tunable spintronic devices. An interesting phenomenon with AHE is the appearance of an additional hump on the respective magnetic films. However, it is still being disputed whether it originates from an intrinsic mechanism of the Berry phase accumulation in real space or is artificially generated by inhomogeneities. This work systematically investigates the magnetism, electronic transport, and Hall effect of $\mathrm{Ni}{\mathrm{Co}}_{2}{\mathrm{O}}_{4}$ (NCO) films with different thicknesses. The investigation reveals that the strong perpendicular magnetic anisotropy, metallic transport, and AHE are coexisting in NCO films. Especially, the sharp spikes in anomalous Hall effect are observed in thinner NCO films. The two-channel AHE model is used to explain the origin of the sharp spikes associated with anomalous Hall effect. It indicates that the phase separation is the reason for the sharp spikes. In addition, the mixed valence state, ferrimagnetic order, and the electronic configuration in NCO films are further analyzed. This study is essential for a comprehensive understanding of NCO films.