Large Increase of a Magnetic Damping Due to the Enhancement of Rashba Orbit Coupling at Bi2Se3/Ag Interface

We study the spin-pumping effect in topological insulator/ferromagnet structures using ferromagnetic resonance (FMR) measurements with a coplanar waveguide (CPW). We compared three different samples: NiFe, Bi Se /NiFe, and Bi Se /Ag/NiFe, where NiFe is a reference sample. Compared with 7 nm thick NiFe, Bi Se /NiFe shows three times larger magnetic damping, which is the consequence of the strong spin pumping effect from NiFe to Bi Se layers. Surprisingly, once 1.5 nm thick Ag inserted between Bi Se and NiFe, we could observe 12 times enlargement of a magnetic damping in Bi Se /Ag/NiFe structure. This observation can be attributed to the enhancement of Rashba orbit coupling at the Bi Se /Ag interface.