Large temperature-dependent spin pumping in topological insulator–ferromagnet bilayers probed by ferromagnetic resonance spectroscopy

Strong bulk spin-orbit coupling and the presence of robust, spin-momentum-locked surface states make topological insulators uniquely advantageous as spin detectors for potential spin-orbitronics applications. In this work, the role of the surface states in the spin-detection functionality is explored by studying the temperature dependence of spin pumping in a BiSbTe1.5Se1.5(BSTS)/Co20Fe60B20(CoFeB) bilayer using ferromagnetic resonance spectroscopy. Across the studied temperature range, significantly broader linewidths are detected in the bilayer sample compared to a reference CoFeB film, while the frequency dependence of linewidths show a linear behavior illustrating that the damping is predominantly Gilbert type. Significant temperature-dependent modification of the Gilbert damping and the resonance condition are observed and further demonstrated to closely correspond to the temperature-dependent transport characteristics. As the temperature decreases below the point where the surface-dominated conduction appears in the resistance vs temperature characteristics, both the damping modulation and the resonance condition show drastic changes, consistent with enhanced dynamical exchange-driven spin-pumping efficiency in the surface-dominated transport regime. Consequently, the room-temperature spin-pumping efficiency, quantified by spin-mixing conductance, is shown to be more than double at low temperatures. locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon Physics Subject Headings (PhySH)Magneto-optical Kerr effectSpin pumpingUltrafast magnetization dynamicsFerromagnetsMagnetic multilayersSolid-state detectorsTopological insulatorsFerromagnetic resonance