Investigation of spin pumping across FeGaB – BiSb interface at two different time scales*

3-D topological insulators (TI) with large spin Hall conductivity have emerged as potential candidates for spintronic applications [1]. Here, we report spin to charge conversion in bilayers of amorphous ferromagnet (FM) Fe₇₈Ga₁₃B₉ (FeGaB) and 3-D TI Bi₈₅Sb₁₅ (BiSb) activated by two complementary techniques: spin pumping and ultrafast spin-current injection. The spin pumping parameters derived from inverse spin Hall effect measurements are consistent with the results of femtosecond light-pulse induced THz emission, successfully verified using theoretical calculations of spin Hall conductivity of BiSb thin films based on tight binding model. Our results suggest that these first-time measurements and theory of spin dynamics from ~ 10 GHz to several THz in a simple but novel and scalable TI-FM interface provide a promising platform for creating novel spin orbit torque devices.

[1] Hasan, et al. Annu. Rev. Condens. Matter Phys. 2.1 (2011): 55-78.