We demonstrate that a distinct high-disorder anomalous Hall effect phase emerges at the correlated insulator threshold of ultrathin, amorphous, ferromagnetic ${\mathrm{CNi}}_3$ films. In the weak-localization regime, where the sheet conductance $G\gg e^2/h$, the anomalous Hall resistance of the films increases with increasing disorder and the Hall conductance scales as $G_{xy}\propto G^{\phi }$ with $\phi =1.6$. However, at sufficiently high disorder the system begins to enter the 2D correlated insulator regime, at which point the Hall resistance $R_{xy}$ abruptly saturates and the scaling exponent becomes $\phi =2$. Tunneling measurements show that the saturation behavior is commensurate with the emergence of the 2D Coulomb gap, suggesting that $e\mathrm{\text{−}}e$ interactions mediate the high-disorder phase.

• Received 9 November 2009

DOI:https://doi.org/10.1103/PhysRevLett.104.076806