We use a simple magnetron sputtering process to fabricate beta (β) tungsten thin films, which are capable of generating giant spin Hall effect. As-deposited thin films are always in the metastable β-W phase from 3.0 to 26.7 nm. The β-W phase remains intact below a critical thickness of 22.1 nm even after magnetic thermal annealing at 280 °C, which is required to induce perpendicular magnetic anisotropy (PMA) in a layered structure of β-W/Co40Fe40B20/MgO. Intensive annealing transforms the thicker films (>22.1 nm) into the stable α-W phase. We analyze the structure and grain size of both β- and α-W thin films. Electron transport in terms of resistivity and normal Hall effect is studied over a broad temperature range of 10 K to at least 300 K on all samples. Very low switching current densities are achieved in β-W/Co40Fe40B20/MgO with PMA. These basic properties reveal useful behaviors in β-W thin films, making them technologically promising for spintronic magnetic random access memories and spin-logic devices.

We have obtained robust perpendicular magnetic anisotropy in β-W/CoFeB/MgO structure without the need of any insertion layer between W and CoFeB. This was achieved within a broad range of W thickness (3.0-9.0 nm) and using a simple fabrication technique. We have determined the spin Hall angle (0.40) and spin diffusion length for the bulk beta form of tungsten with a large spin-orbit coupling. As a result of the Giant Spin Hall Effect in β-W and careful magnetic annealing, we have significantly reduced the critical current density for the spin-transfer torque induced magnetic switching in CoFeB. The elemental β-W is a superior candidate for magnetic memory and spin-logic applications.

Using an optimized fabrication and magnetic thermal annealing process, we have obtained a high quality β-Ta/CoFeB/MgO layered structure with strong spin-orbit coupling. We have studied electron transport, magnetotransport, and magnetic properties of this system over a wide temperature range between 5K and 300 K. We present the results of resistivity, magnetization, Giant Spin Hall Effect (GSHE), perpendicular magnetic anisotropy, and magnetic switching phase diagram. β-Ta exhibits a large spin Hall angle of 0.14, and shows evidence of spin Hall angle's scaling with resistivity quadratically. The optimized β-Ta/CoFeB/MgO system displays the lowest switching current density among similar systems. Our comprehensive study will benefit applications of GSHE in spintronics.