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

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.

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