Effect of sputtering process parameters on tungsten structural phases and its spin Hall angle

Spin-orbit coupling (SOC) plays a crucial role in spin-to-charge interconversion. SOC correlates structural phases of heavy metals (HM) and its spin Hall angle. Here, we report a systematic investigation of the growth of tungsten (W) by tuning sputtering process parameters, and its influence on spin Hall angle (θ
SH
). Surface topographical measurements suggest that nucleation and growth of polycrystalline W follow the Volmer-Weber mechanism. The X-ray diffraction and resistivity results reveal that W exhibits a structural phase transition from mixed (α + β)-W to β-W as a function of Ar deposition pressure (P
Ar
) for a constant thickness. The kinetic energy of sputtered atoms and the adatom's surface mobility determines the phase formation. W deposited with different deposition rates (D
r
) at constant P
Ar
suggests that relative phase fraction is tunable by D
r
where the resistivity measurements confirm the same. From spin-pumping technique, the maximum spin-mixing conductance is found to be 10.1× 10
¹⁸
m
⁻²
. The estimated θ
SH
from inverse spin Hall effect measurements is found to be −0. 24 (± 0.08) at D
r
=0.08 nm/s. Our systematic investigation may improve the understanding on the evolution of W crystalline phases via controlling sputtering process parameters.