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

Abstract

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 ([Formula: see text] on the tungsten (W) crystalline phase and extracted spin-dependent transport parameters. X-ray diffraction results show that 10[Formula: see text]nm-thick W films exhibit a structural phase transition from a mixed phase of [Formula: see text]-W to a single phase of [Formula: see text]-W as a function of [Formula: see text]. The observed phase transition is due to a decrease in adatom’s energy and surface mobility. Interestingly, only the [Formula: see text]-W phase is found to stabilize when W sputtered on a seed Ni[Formula: see text]Fe[Formula: see text] (Permalloy or Py) film. The growth of [Formula: see text]-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 [Formula: see text], in which the [Formula: see text]-W relative phase fraction is relative. A ferromagnetic resonance (FMR)-based spin pumping method was employed for spin current injection. The FMR linewidth ([Formula: see text] is enhanced for Py/W compared to the bare Py layer due to the spin current transport across the interface. The spin-mixing conductance ([Formula: see text] is found to be a function of the relative phase fraction of W. The extracted [Formula: see text] is [Formula: see text][Formula: see text]m[Formula: see text] for [Formula: see text][Formula: see text]mTorr and [Formula: see text][Formula: see text]m[Formula: see text] for [Formula: see text][Formula: see text]mTorr. From the inverse spin Hall effect (ISHE) measurements, the effective spin Hall angle ([Formula: see text] is estimated to be [Formula: see text] for [Formula: see text]-W rich mixed phase of [Formula: see text]-W, whereas it is [Formula: see text] for [Formula: see text]-W rich [Formula: see text]-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.