Reorientable Spin Direction for Spin Current Produced by the Anomalous Hall Effect

TL;DR

This study demonstrates experimentally that the spin direction of spin currents generated by the anomalous Hall effect in ferromagnetic layers can be reoriented by changing the magnetization direction, revealing a new way to control spin-orbit torques.

Contribution

The paper introduces the experimental observation that the spin current's direction from the anomalous Hall effect depends on the magnetization orientation, enabling reorientation of spin currents.

Findings

Spin current direction depends on FeGd magnetization angle.

Spin-orbit torque varies with magnetization orientation.

Angular dependence allows non-zero torque in specific geometries.

Abstract

We show experimentally that the spin direction of the spin current generated by spin-orbit interactions within a ferromagnetic layer can be reoriented by turning the magnetization direction of this layer. We do this by measuring the field-like component of spin-orbit torque generated by an exchange-biased FeGd thin film and acting on a nearby CoFeB layer. The relative angle of the CoFeB and FeGd magnetic moments is varied by applying an external magnetic field. We find that the resulting torque is in good agreement with predictions that the spin current generated by the anomalous Hall effect from the FeGd layer depends on the FeGd magnetization direction $\hat{m}_{FeGd}$ according to $\vec{\sigma}\propto\left ( \hat{y}\cdot \hat{m}_{FeGd} \right )\hat{m}_{FeGd}$, where $\hat{y}$ is the in-plane direction perpendicular to the applied charge current. Because of this angular dependence, the spin-orbit torque arising from the anomalous Hall effect can be non-zero in a sample geometry for which the spin Hall torque generated by non-magnetic materials is identically zero.