Saturation of the Anomalous Hall Effect in Critically Disordered Ultra-thin CNi3 Films

TL;DR

This study reveals a high-disorder anomalous Hall effect phase in ultra-thin amorphous CNi3 films, where Hall resistance saturates at the correlated insulator threshold, linked to Coulomb gap formation.

Contribution

It uncovers a distinct high-disorder phase with saturated Hall resistance and a new scaling behavior at the insulator transition in amorphous ferromagnetic films.

Findings

Hall resistance saturates at high disorder

Hall conductance scales as G^1.6 in weak localization regime

Saturation correlates with Coulomb gap emergence

Abstract

We demonstrate that a distinct high-disorder anomalous Hall effect phase emerges at the correlated insulator threshold of ultra-thin, amorphous, ferromagnetic CNi3 films. In the weak localization regime, where the sheet conductance G >> e^2/h, the anomalous Hall resistance of the films increases with increasing disorder and the Hall conductance scales as Gxy ~ G^1.6. However, at sufficiently high disorder the system begins to enter the 2D correlated insulator regime, at which point the Hall resistance Rxy abruptly saturates and the scaling exponent becomes 2. Tunneling measurements show that the saturation behavior is commensurate with the emergence of the 2D Coulomb gap, suggesting that e-e interactions mediate the high-disorder phase.