Magnetotransport studies of strongly disordered annealed amorphous Fe/Si multilayers

Temperature Dependence of the Anomalous Hall Effect from Electron Interactions

We consider the impact of electron-electron interactions on the temperature dependence of the anomalous Hall effect in disordered conductors. The microscopic analysis is carried out within the diagrammatic approach of the linear response Kubo-Streda formula with an account of both extrinsic skew-scattering and side-jump mechanisms of the anomalous Hall effect arising in the presence of spin-orbit coupling. We demonstrate the importance of electron interactions in the Cooper channel even for nominally non-superconducting materials and find that the corresponding low-temperature dependence of the anomalous Hall conductivity is asymptotically of the form sqrt[T]/ln(T_{0}/T) in three dimensions and ln[ln(T_{0}/T)] in two dimensions, where the scale of T_{0} is parametrically of the order of Fermi energy. These results, in particular, may provide a possible explanation for the recently observed unconventional temperature dependence of the anomalous Hall effect in HgCr_{2}Se_{4}.

Saturation of the anomalous Hall effect in critically disordered ultrathin CNi3 films

We demonstrate that a distinct high-disorder anomalous Hall effect phase emerges at the correlated insulator threshold of ultrathin, 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 G{xy} proportional to 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-e interactions mediate the high-disorder phase.

Weak-localization correction to the anomalous Hall effect in polycrystalline fe films

In situ transport measurements have been made on ultrathin (<100 A thick) polycrystalline Fe films as a function of temperature and magnetic field for a wide range of disorder strengths. For sheet resistances Rxx less than approximately 3kOmega, we find a logarithmic temperature dependence of the anomalous Hall conductivity sigmaxy, which is shown for the first time to be due to a universal scale dependent weak-localization correction within the skew-scattering model. For higher sheet resistance, granularity becomes important and the break down of universal behavior becomes manifest as the prefactors of the lnT correction term to sigmaxx and sigmaxy decrease at different rates with increasing disorder.