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) bilayer at room temperature. V-ISHE of up to 63.4 +/- 4.0 mu V 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 mu V 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. (C) 2015 AIP Publishing LLC.