  Spin-orbit torque manifested as an accumulated spin-polarized moment at
nonmagnetic normal metal, and ferromagnet interfaces is a promising
magnetization switching mechanism for spintronic devices. To fully exploit this
in practice, materials with a high spin Hall angle, i.e., a charge-to-spin
conversion efficiency, are indispensable. To date, very few approaches have
been made to devise new nonmagnetic metal alloys. Moreover, new materials need
to be compatible with semiconductor processing. Here we introduce W-Ta and W-V
alloys and deploy them at the interface between $\beta$-W/CoFeB layers. First,
spin Hall conductivities of W-Ta and W-V structures with various compositions
are carried out by first-principles band calculations, which predict the spin
Hall conductivity of the W-V alloy is improved from $-0.82 \times 10^3$ S/cm
that of W to $-1.98 \times 10^3$ S/cm. Subsequently, heterostructure
fabrication and spin-orbit torque properties are characterized experimentally.
By alloying $\beta$-W with V at a concentration of 20 at%, we observe a large
enhancement of the absolute value of spin Hall conductivity of up to $-(2.77
\pm 0.31) \times 10^3$ S/cm. By employing X-ray diffraction and scanning
transmission electron microscopy, we further explain the enhancement of
spin-orbit torque efficiency is stemmed from W-V alloy between W and CoFeB.
