Effect of Ta capping layer on spin dynamics in Co50Fe50 thin films

Abstract

Spin pumping induced non-equilibrium spin accumulation at the interface shows an anomalous anti-damping effect for heavy metal nonmagnetic layer deposited on a ferromagnetic layer at the spin diffusion length regime without application of any external electrical current. In this work, we report a comprehensive study of static and dynamic magnetic properties of Co50Fe50 (20 nm)/Ta (t nm) thin films where the thickness of the Ta layer was varied as t = 0, 2, 5, 10, 20 and 30 nm. Ferromagnetic resonance measurements revealed a significant reduction of Gilbert damping parameter for CoFe (20 nm)/Ta (2 nm) sample in comparison to bare CoFe (20 nm) sample due to interfacial Rashba spin-orbit interaction accompanied by the formation of Ta2O5 as evidenced by x-ray photoelectron spectroscopy. The extrinsic contributions to Gilbert damping were ruled out in our samples with the invariance of resonance fields and linear increment of linewidth with frequency for different thicknesses of Ta. The saturation magnetization of the bare Co50Fe50 (20 nm) sample was found out to be 1831 ± 54 mT without any annealing effect or seed layer. Maximum spin mixing conductance of −31.46 × 1018 m−2 was found for CoFe (20 nm)/Ta (2 nm) sample, whereas it was nearly constant for all other samples.