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

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 ( ρ W ) of β -W films. Different resistivity ranging from 100 μ Ω-cm to 1400 μ Ω-cm with a thickness of 8 nm can be achieved by varying the argon pressure ( P Ar ) during the growth by the method of sputtering. The coefficient of effective damping α eff is observed to increase from 0.010 to 0.025 with ρ W , which can be modulated by P Ar . We observe a modest dependence of α eff on the sputtering power ( p S ) while keeping the P Ar constant. α eff dependence on both P Ar and p S suggests that there exists a strong correlation between α eff and ρ W . It is thus possible to utilize ρ W as a tuning parameter to regulate the α eff , 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 ( J S ( eff ) ) is also evaluated by considering the spin-back flow in this process. Intrinsic spin mixing conductance ( g W ↑ ↓ ) and spin diffusion length ( λ SD ) 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 α eff which is quite different from α b of single Py layer and the enhancement in α eff at low temperature can be attributed to the spin-induced pumping from Py layer into β -W.