Influences of Structure on Intrinsic Spin Hall Conductivity of W-N alloys

In recent works, W alloys have drawn attention in spintronics due to their high spin Hall angle up to ≈0.6 [1-3]. Here, the spin Hall conductivities (σ_xy) of W-N alloys are investigated using first-principles calculations. Most probable W is α-W in bcc structure, whereas β-W in A15 structure is metastable, but exhibits σ_xy -817 S/cm, larger than α-W. Among various compositions of W-N alloys [4,5], only W₂N and WN are explored for their σ_xy due to their phase stability. WN, having three possible structures, has σ_xy = -194 S/cm by thermodynamic average. Notably, W₂N in NaCl structure with 50% N vacancy, exhibits the largest σ_xy = -966 S/cm among W-N alloys, enhanced by 18 % over β-W. This large σ_xy is elucidated by the large Berry curvature around 2/3ΓX. The lifted degeneracy at 2/3ΓX is analyzed with group theory, where the Fermi level crosses the gap; thereby, only negative Berry curvature survives giving large σ_xy.

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