Anomalous spin Hall angle of a metallic ferromagnet determined by a multiterminal spin injection/detection device*

We report on the determination of the anomalous spin Hall angle in the ferromagnetic metal alloy cobalt-iron (Co₂₅Fe₇₅, CoFe). This is accomplished by measuring the spin injection/detection efficiency in a multiterminal device with nanowires of platinum (Pt) and CoFe deposited onto the magnetic insulator yttrium iron garnet (Y₃Fe₅O₁₂, YIG). Applying a spin-resistor model to our multiterminal spin transport data, we determine the magnon conductivity in YIG, the spin conductance at the YIG/CoFe interface and finally the anomalous spin Hall angle of CoFe as a function of its spin diffusion length in a single device. Our experiments clearly reveal a negative anomalous spin Hall angle of the ferromagnetic metal CoFe, but a vanishing ordinary spin Hall angle. This work therefore adds new observations to the results reported in Refs. [1,2], where the authors found finite contributions of the ordinary spin Hall angle in the ferromagnetic metals Co and permalloy.

[1] D. Tian et al., Phys. Rev. B 94, 020403 (2016).
[2] K. S. Das et al., Phys. Rev. B 96, 220408 (2017)