A multi-code investigation of promising spin Hall materials

Abstract

Listen

Translate article

The spin Hall effect (SHE) is a phenomenon with vast potential for application in spintronic memory devices. Spin Hall materials based on alloys show great promise due to the ability to tune the resistance and spin Hall conductivity as a function of composition. However, predicting and optimizing the total spin Hall conductivity can be challenging due to the complex interactions between intrinsic (band-related) and extrinsic (skew scattering) contributions to spin Hall conductivity. Over the years, different numerical methods have been optimised for distinct SHE mechanisms or configurations. Using a multi-code approach can provide us with a comprehensive framework to address and optimize all aspects of spin Hall conductivity in complex alloys. Tungsten in its β phase has a particularly large spin Hall effect (SHE) and therefore has potential application in future low power, high endurance MRAM devices. In this study, we used the screened Korringa-Kohn-Rostocker (KKR) method [1] along with the linearized Boltzmann Transport equation, Quantum Espresso [2] and PAOFLOW [3] to reveal how dilute N or O impurities affect both the intrinsic and extrinsic SHE in the bcc (α) and β phase tungsten [4]. Our results, when examined in combination, suggest that the formation of grain boundaries in the doped system plays an important role in amplifying the SHE in β tungsten. Further techniques such as the coherent potential approximation [5,6] enables us to treat not only dilute but concentrated alloys as well. With this expanded tool set, an even wider array of other spintronic materials, such as Pt based alloys will be explored. [1] L. Peti et al, Philos. Mag. B 78, (1998) 449 [2] P. Gianozzi et al, J. Phys.: Condens. Matt. 21, (2009) 395502 [3] M. B. Nardelli et al, Comp. Mat. Sci. 143, (2018) 462-472 [4] O. L. W. McHugh, M. Gradhand, W.-F. Goh and D. A. Stewart, Phys. Rev. Mat. 4, (2020) 094404 [5] D. Ködderitzsch, H. Ebert, D. A. Rowlands, A. Ernst, New J. of Phys. 9(4), 2007, 81-81 [6] P. R. Tulip et al, Phys. Rev. B 77, 2008, 165116