Abstract
Elemental tin in the α‐phase is an intriguing member of the family of topological quantum materials. In thin films, with decreasing thickness, α‐Sn transforms from a 3D topological Dirac semimetal (TDS) to a 2D topological insulator (TI). Getting access to and making use of its topological surface states is challenging and requires interfacing to a magnetically ordered material. Herein, the successful epitaxial growth of α‐Sn thin films on Co, forming the core of a spin‐valve structure, is reported. Time‐ and element‐selective ferromagnetic resonance experiments are conducted to investigate the presence of spin pumping through the spin‐valve structure. A rigorous statistical analysis of the experimental data using a model based on the Landau–Lifshitz–Gilbert–Slonczewski equation is applied. A strong exchange coupling contribution is found, however no unambiguous proof for spin pumping. Nevertheless, the incorporation of α‐Sn into a spin valve remains a promising approach given its simplicity as an elemental TI and its room‐temperature application potential.
Highlights
Topological insulators (TIs)[1]—a class of materials that are insulating in their bulk and conducting on their surface[2]—hold great promise for revolutionizing spintronics and other fields of emerging electronics
Theoretical model optimization allowed for determination of the exchange coupling parameter J, which was in the range between 2.5 and 6.5 mT
By comparing this value with an MgO interlayer–based magnetic tunnel junction of similar thickness (JMgO % 1.0 mT), it can be concluded that α-Sn spin valves exhibit much stronger exchange coupling between the magnetic layers
Summary
InSb(111) above a critical thickness have shown 3D-topological Dirac semimetal (TDS) states.[19]. Www.advancedsciencenews.com www.pss-rapid.com pumped from an FM layer undergoing ferromagnetic resonance (FMR) into an adjacent layer.[29] Spin pumping is commonly studied via the broadening of the magnetic resonance, whereby it manifests itself as an additional damping term in the magnetodynamic equations.[30] Spin pumping from an Fe layer via Ag into an 30-monolayer-thick α-Sn film had been demonstrated in 2016,[31] which was very recently complemented by the demonstration of spin pumping into its 3D-TDS state.[32] Apart from this indirect way of studying spin currents, direct confirmation can be obtained by pumping the spin current through a nonmagnetic spacer layer into a second FM layer, which is not at resonance.[33] In such a spin-valve structure, the amplitude and phase of the precession of the nonresonant layer are analyzed, allowing for a direct probing of the coupling mechanisms between the layers, and for an unambiguous proof of spin pumping.[34] In this context, TI layers offer exciting prospects given their spin– momentum locked surface states,[35,36] and the investigation of a TI-based spin-valve has been reported earlier.[37]. We find no clear evidence for spin pumping through the α-Sn layer, which could be explained by dynamic exchange[39] or by the limited number of current paths in this 2D-TI
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