In the course of searching for promising topological materials for applications in future topological electronics, we evaluated spin-orbit torques (SOTs) in high-quality sputtered δ-TaN/${\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$ devices through spin-torque ferromagnetic resonance (ST-FMR) and spin pumping measurements. From the ST-FMR characterization we observed a significant linewidth modulation in the magnetic ${\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$ layer attributed to the charge-to-spin conversion generated from the δ-TaN layer. Remarkably, the spin-torque efficiency determined from ST-FMR and spin pumping measurements is as large as $\mathrm{\Theta }=$ 0.034 and 0.031, respectively. These values are over two times larger than for α-Ta, but almost five times lower than for β-Ta, which can be attributed to the low room temperature electrical resistivity $\sim 74\mu \mathrm{\Omega }\mathrm{cm}$ in δ-TaN. A large spin diffusion length of at least $\sim 8\mathrm{nm}$ is estimated, which is comparable to the spin diffusion length in pure Ta. Comprehensive experimental analysis, together with density functional theory calculations, indicates that the origin of the pronounced SOT effect in δ-TaN can be mostly related to a significant contribution from the Berry curvature associated with the presence of a topically nontrivial electronic band structure in the vicinity of the Fermi level ($E_{\mathrm{F}}$). Through additional detailed theoretical analysis, we also found that an isostructural allotrope of the superconducting δ-TaN phase, the simple hexagonal structure θ-TaN, has larger Berry curvature, and that, together with expected reasonable charge conductivity, it can also be a promising candidate for exploring a generation of spin-orbit torque magnetic random access memory as cheap, temperature stable, and highly efficient spin current source.

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• Electronic structure
• First-principles calculations
• Spin Hall effect
• Spin current
• Spin pumping
• Spin torque
• Spin transfer torque
• Spin-orbit coupling
• Superconductivity
• Topological materials
• Superconductors
• Ferromagnetic resonance
• Sputtering