Enhancement of damping factor in Fe/Bi₂Se₃ heterostructures via topological surface states modification

Owing to the spin-momentum-locked surface state of topological insulators (TIs), the spin dynamics in ferromagnetic materials(FM)/TI heterostructures is expected to be significantly different with that in FM/non-magnetic heavy metals. Previous studies suggested that TI can modulate the spin dynamics of FM layer, however, the temperature dependence of damping factors is controversial. Here, we report spin dynamics in Fe/Bi₂Se₃ heterostructures by changing thickness of Bi₂Se₃ with and without topological surface state (TSS). Compared with that in Fe/Bi₂Se₃(3QL), where Bi₂Se₃ containing only bulk state without TSS, a significant enhancement of damping factor was achieved in Fe/Bi₂Se₃(9QL) by TSS of Bi₂Se₃. On the basis of ab initio electronic structure calculations, we confirm that the enhancement of damping factor is originated from the strong band hybridizations of Fe and Bi₂Se₃(9QL) near the Fermi level. Furthermore, by inserting Cu layer between Fe and Bi₂Se₃, the contribution of spin pumping and magnetic proximity effect to the overall damping factor was separated. Our work not only reveals the mechanism of TSS-induced damping factor, but provides a new freedom to tailor the damping factor of FM/TI spintronic devices as well.