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 (VISHE) were detected in Bi2Se3(001)/Fe3Si(111) bi-layer at room temperature. VISHE of up to 63.4 ± 4.0 μV at 100 mW microwave power (PMW) was observed. In addition, Fe(111)/Bi2Te3(001) bi-layer also showed a large VISHE of 3.0 ± 0.1 μV at PMW of 25 mW. VISHE 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 (Jc) 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.