Deposition Pressure Dependence on Spin Hall Angle of W Thin Films Grown on NiFe.

Spin-to-charge conversion and vice versa due to spin-orbit coupling in ferromagnet-heavy metal heterostructure is of paramount interest for developing energy-efficient spintronic devices. Here, we have systematically investigated the effect of Ar deposition pressure ( P Ar ) on the tungsten (W) crystalline phase and extracted spin-dependent transport parameters. X-ray diffraction results show that 10 nm-thick W films exhibit a structural phase transition from a mixed phase of (α + β) -W to a single phase of β -W as a function of P Ar . The observed phase transition is due to a decrease in adatom's energy and surface mobility. Interestingly, only the (α + β) -W phase is found to stabilize when W sputtered on a seed Ni 8 0 Fe 2 0 (Permalloy or Py) film. The growth of (α + β) -W on the seed Py layer could be due to the strain that facilitates the mixed phase. W deposited on the Py layer is shown to be dependent on P Ar , in which the β -W relative phase fraction is relative. A ferromagnetic resonance (FMR)-based spin pumping method was employed for spin current injection. The FMR linewidth (Δ H) is enhanced for Py/W compared to the bare Py layer due to the spin current transport across the interface. The spin-mixing conductance ( g ↑ ↓) is found to be a function of the relative phase fraction of W. The extracted g ↑ ↓ is 4. 9 0 × 1 0 1 8 m − 2 for P Ar = 5 mTorr and 4. 0 5 × 1 0 1 8 m − 2 for P Ar = 1 0 mTorr. From the inverse spin Hall effect (ISHE) measurements, the effective spin Hall angle ((θ SH ) is estimated to be − 0. 1 7 for α -W rich mixed phase of (α + β) -W, whereas it is − 0. 1 0 for β -W rich (α + β) -W. Our systematic study demonstrates the relatively large effective spin Hall angle via low-longitudinal resistivity by controlling the relative phase fraction of W and helps in developing energy-efficient spintronic devices. [ABSTRACT FROM AUTHOR]