Scaling of the anomalous Hall effect in perpendicularly magnetized epitaxial films of the ferrimagnet NiCo2O4

We investigate the anomalous Hall effect in perpendicularly magnetized ferrimagnet NiCo2O4 epitaxial films 3 to 30 nm thick. We find that the anomalous Hall conductivity sigma(AHE) has complex relations with the longitudinal electrical conductivity sigma(xx). When the sigma(xx) is relatively large (larger than 10(3) Omega(-1) cm(-1)), the sigma(AHE) is almost independent of the sigma(xx), but scales with the magnetization. This unique scaling behavior of sigma(AHE) indicates that the anomalous Hall effect is of intrinsic origin dominated by the Berry curvature of occupied electronic states. On the other hand, when the sigma(xx) is lowered, the scaling relation is changed to sigma(AHE) similar to sigma(1.6)(xx), indicating a crossover of the dominant contribution to sAHE, from the intrinsic Berry phase to the impurity scatterings. Our results show the intrinsic contribution from Berry curvature plays a crucial role in the anomalous Hall effect in NiCo2O4 films.