Doping-induced enhancement of anomalous Hall coefficient in Fe-Sn nanocrystalline films for highly sensitive Hall sensors

Abstract

We experimentally investigated the contribution of intrinsic anomalous Hall effect (AHE) in ferromagnetic Fe-Sn nanocrystalline films by means of impurity doping. We found that some heavy transition elements such as Ta, W, and Mo are effective for increasing the anomalous Hall resistivity of Fe-Sn films. The concomitant decrease in magnetization of the Fe-Sn matrix indicated that the increased anomalous Hall resistivity arises from the enhancement of the anomalous Hall coefficient. The increased anomalous Hall resistivity, in combination with the moderately decreased saturation field, substantially increased the derivative of anomalous Hall resistivity with respect to applied magnetic field in the linear Hall response region at low field, which corresponds to the sensitivity in an AHE-type Hall sensor. In particular, optimally Ta-doped Fe-Sn films showed nearly doubled sensitivity in comparison with nondoped Fe-Sn films, while the virtually temperature-independent behavior of the sensitivity was maintained between 400 and 50 K. These improved AHE characteristics enable sensitive detection of magnetic field over a wide temperature range. We discuss that strong spin-orbit coupling inherent to these heavy transition elements contributes to the modification of electronic structure, inducing the large intrinsic AHE. The doping technique demonstrated will be a fundamental strategy for exploiting the performance of Fe-Sn metal-based AHE-type Hall sensors.