Magnetization-Independent Spin Hall Effect in Ferromagnetic Metals

The anomalous spin Hall effect, which creates charge-to-spin conversion in metallic ferromagnets, offers an exciting opportunity to generate spin currents for which the spin direction is controllable. Here we report spin-torque ferromagnetic resonance measurements of current-induced torques in ferromagnet-spacer-ferromagnet trilayers with NiFe, Co and CoFeB as our magnetic layers, allowing us to clearly separate signals from the different ferromagnetic layers. We observe signals with the symmetry of a magnetization-independent spin Hall effect with spin-to-charge efficiencies as large as 10% in NiFe, which is comparable to heavy metal-ferromagnet bilayers investigated previously. This research illustrates some of the competing effects which must be considered when investigating spin-to-charge conversion in ferromagnets, and also confirms that the spin current polarization and local magnetic moment in a ferromagnet do not need to be aligned.