Large Spin Hall Angle in β-W Thin Films Grown on CoFeB without Oxygen Plasma

Abstract

We report on growth optimization and magnetodynamic properties of [Formula: see text]-W/Co[Formula: see text]Fe[Formula: see text]B[Formula: see text] system. We show that a relatively low growth rate of [Formula: see text][Formula: see text]Å/s is essential for the stabilization of the [Formula: see text] phase of tungsten. The low growth rate allows for the residual oxygen present in the chamber to get incorporated into the growing film, which helps in the stabilization of [Formula: see text]-phase tungsten as evidenced by X-ray diffraction and X-ray photoelectron spectroscopy. Using these optimized growth conditions, we achieved the [Formula: see text] phase in tungsten thin films up to a thickness of 60[Formula: see text]nm. The ferromagnetic resonance measurements of [Formula: see text]-W/Co[Formula: see text]Fe[Formula: see text]B[Formula: see text] show a linear behavior of the Gilbert damping constant with the inverse of the thickness of the CoFeB layer, from which, we calculated spin mixing conductance to be [Formula: see text][Formula: see text]m[Formula: see text]. Using the inverse spin Hall effect measurements, we obtained a large spin Hall angle of [Formula: see text] in [Formula: see text]-W, which is achieved without using oxygen plasma during growth of tungsten.