Growth dependent structural ordering and stability in sputtered grown β tungsten thin films for Spintronic applications

Spintronic is an emerging field for the next generation spin-based nanodevices. Heavy metals like tungsten (W) can generate nonequilibrium spins via the spin Hall effect. Recently, the β phase of W has emerged as a potential candidate for spintronic applications due to its higher spin Hall angle compared to the other elemental solids and large spin-orbit torque. However, ideally, it is a metastable phase, and its stability is found to be due to the presence of oxygen. We have shown the efficient ability of the dc magnetron sputtering technique to grow a stable β-W film at room temperature by varying a set of deposition parameters. The atomic strcuture of the films and the existence of the β phase have been recognized from the synchrotron-based X-ray diffraction studies. The stability and atomic structure of the β phase have been further confirmed from the ab-initio molecular dynamics simulations, which show the presence of oxygen is to be very important for the stability of this phase. Simulation with different oxygen concentrations suggests about 20 at.% oxygen for the β phase formation. This agrees well with the experimental findings