Spin Pumping Response of Fe₇₅Co₂₅/Bi₂Te₃ at Microwave and Optical Excitations

In recent years, the techniques of differing timescales have been used to study the spin-to-charge conversion processes driven by the bulk spin Hall effect or by broken inversion symmetry at interfaces [1]. Here we report our studies of spin pumping at the interface of epitaxial ferromagnet Fe₇₅Co₂₅ and a three-dimensional topological insulator Bi₂Te₃. The spin injection phenomenon has been quantified using two complimentary techniques: one involving ferromagnetic resonance (FMR) driven inverse spin Hall effect (ISHE) measurement at GHz frequencies and the other monitoring terahertz (THz) radiation emission driven by femtosecond light pulses of 800 nm radiation. The spin to charge conversion has been analyzed in the framework of a spin diffusion model. The key result of this investigation is that regardless of the two different spin excitation methods used, the spin diffusion length comes out to be comparable for the GHz and THz timescale measurements. Our results aid in understanding the role of various spin excitation mechanisms and their contribution to ISHE in FM-TI interfaces.

References

[1] V. Sharma, P. Bajracharya, A. Johnson, and R.C. Budhani, AIP Adv. 12, 35028 (2022).