Abstract
Topological insulators (TIs) are enticing prospects for the future of spintronics due to their large spin-orbit coupling and dissipationless, counter-propagating conduction channels in the surface state. However, a means to interact with and exploit the topological surface state remains elusive. Here, we report a study of spin pumping at the TI-ferromagnet interface, investigating spin transfer dynamics in a spin-valve like structure using element specific time-resolved x-ray magnetic circular dichroism, and ferromagnetic resonance. Gilbert damping increases approximately linearly with increasing TI thickness, indicating efficient behaviour as a spin sink. However, layer-resolved measurements suggest that a dynamic coupling is limited. These results shed new light on the spin dynamics of this novel material class, and suggest great potential for TIs in spintronic devices, through their novel magnetodynamics that persist even up to room temperature.
Highlights
Topological insulators (TIs) are enticing prospects for the future of spintronics due to their large spin-orbit coupling and dissipationless, counter-propagating conduction channels in the surface state
We report a study of spin pumping at the TI-ferromagnet interface, investigating spin transfer dynamics in a spin-valve like structure using element specific time-resolved x-ray magnetic circular dichroism, and ferromagnetic resonance
In the prototypical three-dimensional TI Bi2Se3 a large spin-orbit interaction leads to a band inversion in the bulk and the formation of a topologically protected surface state (TSS), with fully spin-polarised counter-propagating conduction channels that are robust against scattering from non-magnetic impurities[10]
Summary
A key focus of spintronic research in recent years has been the phenomenon of spin pumping[17,18], whereby the ferromagnetic resonance (FMR) generates a pure spin current that enters adjacent layers[19] Such non-local spin dynamics manifest as an additional damping term in the Landau-Lifshitz-Gilbert (LLG) equation for magnetodynamics[20], broadening the measured resonance. The application of this technique to TIs is quite naturally suggested by the similarity between the spin-locked surface state of a TI and the separation of angular momentum and charge flow that takes place in a pure spin current Studies of such exciting effects have begun to emerge through electrical transport and inverse spin-hall effect measurements[13,22,23], demonstrating the great potential of TIs for incorporation into spintronic devices such as spin valves. This equation can be readily modified to include spin pumping; for a trilayer structure with only one layer, i, on resonance, the motion of magnetisation
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