Room temperature spin-orbit torque efficiency in sputtered low-temperature superconductor delta-TaN

Abstract

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 $\delta -$TaN/Co20Fe60B20 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 Co20Fe60B20 layer attributed to the charge-to-spin conversion generated from the $\delta -$TaN layer. Remarkably, the spin-torque efficiency determined from ST-FMR and spin pumping measurements is as large as $\Theta =$ 0.034 and 0.031, respectively. These values are over two times larger than for $\alpha -$Ta, but almost five times lower than for $\beta -$Ta, which can be attributed to the low room temperature electrical resistivity $\sim 74\mu \Omega$ cm in $\delta -$TaN. A large spin diffusion length of at least $\sim 8$ 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 $\delta -$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 (EF). Through additional detailed theoretical analysis, we also found that an isostructural allotrope of the superconducting $\delta -$TaN phase, the simple hexagonal structure, $\theta -$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 sources.

28 pages, 7 figures

References in corpus (19)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Advanced capabilities for materials modelling with Quantum ESPRESSO
• Spin Transfer Torques
• Topological Semimetals
• Superconducting properties and Hall Effect of epitaxial NbN thin films
• The 2021 Quantum Materials Roadmap
• Spin Hall Switching of the Magnetization in Ta/TbFeCo Structures with Bulk Perpendicular Anisotropy
• Experimental Demonstration of the Co-existence of the Spin Hall and Rashba Effects in beta-Tantalum/Ferromagnet Bilayers
• Topological Semimetal Nanostructures: From Properties to Topotronics
• Shubnikov-de Haas oscillations, weak antilocalization effect and large linear magnetoresistance in the putative topological superconductor LuPdBi
• Weak Localization and Antilocalization in Nodal-Line Semimetals: Dimensionality and Topological Effects
• Magnetic asymmetry induced anomalous spin-orbit torque in IrMn
• Spin transport parameters of NbN thin films characterised by spin pumping experiments
• Materials Requirements of High-Speed and Low-Power Spin-Orbit-Torque Magnetic Random-Access Memory
• Observation of coexisting weak localization and superconducting fluctuations in strained Sn1-xInxTe thin films
• Crossover Between Weak Antilocalization and Weak Localization and Electron-Electron Interaction in Few-Layer WTe${}_2$
• Giant magnetoresistance, Fermi surface topology, Shoenberg effect and vanishing quantum oscillations in type-II Dirac semimetal candidates MoSi${}_2$ and WSi${}_2$
• Large spin to charge conversion in topological superconductor \b{eta}-PdBi2 at room temperature
• Spin Hall effect generated by fluctuating vortices in type-II superconductors