Modulating Spin Current Induced Effective Damping in β-W/Py Heterostructures by a Systematic Variation in Resistivity of the Sputtered Deposited β-W films

Abstract Utilizing the spin-induced pumping from a ferromagnet (FM) into a heavy metal (HM) under the ferromagnetic resonance (FMR) condition, we report an enhancement in effective damping in β- W/Py bilayers by systematically varying resistivity (ρW) of β-W films. Different resistivity ranging from 100 μΩ-cm to 1400 μΩ-cm with a thickness of 8 nm can be achieved by varying the argon pressure (PAr) during the growth by the method of sputtering. The coefficient of effective damping αeff is observed to increase from 0.010 to 0.025 with ρW, which can be modulated by PAr. We observe a modest dependence of αeff on the sputtering power (pS) while keeping the PAr constant. αeff dependence on both PAr and pS suggests that there exists a strong correlation between αeff and ρW. It is thus possible to utilize ρW as a tuning parameter to regulate the αeff, which can be advantageous for faster magnetization dynamics switching. The thickness dependence study of Py in the aforementioned bilayers manifests a higher spin mixing conductance (g↑↓ eff) which suggests a strong spin pumping from Py into the β-W layer. The effective spin current (JS(eff)) is also evaluated by considering the spin-back flow in this process. Intrinsic spin mixing conductance (g↑↓ W) and spin diffusion length (λSD) of β-W are additionally investigated using thickness variations in β-W. Furthermore, the low-temperature study in β-W/Py reveals an intriguing temperature dependence in αeff, which is quite different from αb of single Py layer and the enhancement in αeff at low temperature can be attributed to the spin-induced pumping from Py layer into β-W.