All-optical observation of giant spin transparency at the topological insulator BiSbTe1.5Se1.5/Co20Fe60B20 interface

Abstract The rise of three-dimensional topological insulators as an attractive playground for the observation and control of various spin-orbit effects has ushered in the field of topological spintronics. To fully exploit their potential as efficient spin-orbit torque generators, it is crucial to investigate the efficiency of spin injection and transport at various topological insulator/ferromagnet interfaces, as characterized by their spin-mixing conductances and interfacial spin transparencies. Here, we use all-optical time-resolved magneto-optical Kerr effect magnetometry to demonstrate efficient room-temperature spin pumping in Sub/BiSbTe 1.5 Se 1.5 (BSTS)/Co 20 Fe 60 B 20 (CoFeB)/SiO 2 thin films. From the modulation of Gilbert damping with BSTS and CoFeB thicknesses, the spin-mixing conductances of the BSTS/CoFeB interface and the spin diffusion length in BSTS are determined. For BSTS thicknesses far exceeding the spin diffusion length, in the so-called “perfect spin sink” regime, we obtain an interfacial spin transparency as high as 0.9, promoting such systems as scintillating candidates for spin-orbitronic devices.