Crossover behavior of the anomalous Hall effect in Ga1−xMnxAs1−yPy across the metal-insulator transition

Quaternary alloy Ga1−xMnxAs1−yPy hosts magnetic and electronic properties that can be tuned by varying the P concentration "y", Mn concentration "x" and by annealing. In this work we make use of this tunability to probe the origin of the anomalous Hall effect (AHE) in Ga1−xMnxAs1−yPy thin films grown on GaAs that host perpendicular magnetic anisotropy. Specifically, we find that AHE in this class of materials is determined primarily by two contributions: an intrinsic band component arising from the Berry curvature, and a component determined by hopping conduction. As we vary the properties of Ga1−xMnxAs1−yPy from the metallic to the semi-insulating regime by changing the value of y and by postgrowth annealing, we observe a clear crossover from a Berry-curvature-induced AHE to one that is caused by hopping. The transition occurs approximately at the point where the numbers of localized and itinerant holes become comparable. In this hopping regime, the conductivity follows the Efros-Shklovskii scaling law versus temperature indicating the presence of a Coulomb gap, but the AHE remains robustly present. These results indicate that Ga1−xMnxAs1−yPy can host an interesting interplay between magnetism and Coulomb interactions.