Strongly enhanced spin current in topological insulator/ferromagnetic metal heterostructures by spin pumping

Spin pumping effect in Bi₂Se₃/Fe₃Si and Fe/Bi₂Te₃ heterostructures was studied. High quality films of Bi₂Se₃(001) on ferromagnetic Fe₃Si(111) layer and Fe(111) films on Bi₂Te₃(001) layer were grown epitaxially by molecular beam epitaxy. Using a microwave cavity source, large voltages due to the Inverse Spin Hall Effect (V_ISHE) were detected in Bi₂Se₃(001)/Fe₃Si(111) bi-layer at room temperature. V_ISHE of up to 63.4 ± 4.0 μV at 100 mW microwave power (P_MW) was observed. In addition, Fe(111)/Bi₂Te₃(001) bi-layer also showed a large V_ISHE of 3.0 ± 0.1 μV at P_MW of 25 mW. V_ISHE of both structures showed microwave linear power dependence in accordance with the theoretical model of spin pumping. The spin Hall angle was calculated to be 0.0053 ± 0.002 in Bi₂Se₃ and was estimated to be 0.0068 ± 0.003 in Bi₂Te₃. The charge current density (J_c) of Bi₂Se₃/Fe₃Si and Fe/Bi₂Te₃ structures are comparable and are about 2–5 times higher than the Fe₃Si/normal metal and Fe₃Si/GaAs results. The significant enhancement of spin current in topological insulator/ferromagnetic metal (TI/FM) and FM/TI bilayers is attributed to strong spin-orbit coupling inherent of TIs and demonstrates the high potential of exploiting TI-based structures for spintronic applications