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| Home > Publications database > Thermal and electrical spin-orbit torques in collinear and noncollinear magnets |
| Conference Presentation (Invited) | FZJ-2017-04126 |
2017
Abstract: While spin-orbit torques [1] in magnetic bilayers composed of a 5d transition metal layer and a ferromagnetic layer can serve as a competitive alternative to the Slonczewski spin-transfer torque in spin-valves and magnetic tunnel junctions in order to realize MRAM devices, spin-orbit torques have even more potential, and are a potential game-changer, in antiferromagnetic spintronics [2] and in noncollinear magnets. After discussing the theory of thermal and electrical spin-orbit torques in collinear magnets, we will shift the focus to current-induced torques and spin-orbit driven effects in noncollinear magnetic bilayers. The combination of structural inversion asymmetry present in the bilayer geometry with noncollinear magnetism leads to several additional spin-orbit driven effects, such as the Dzyaloshinskii-Moriya interaction [3,4,5,6] and chiral damping [7], which join the other effects and current-induced torques important in noncollinear magnets and magnetic bilayers, such as spin-transfer torque, spin-orbit torque and nonadiabatic torque. In particular the combined action of the Dzyaloshinskii-Moriya interaction and the spin-orbit torque from the spin Hall effect enables current-driven domain-wall motion at ultrahigh speeds [8,9]. The large number of current-induced torques and spin-orbit driven effects participating in the current-induced motion of domain-walls or skyrmions are difficult to disentangle and to quantify in experimental measurements. First-principles density functional theory is an ideal tool to understand and to quantify these effects. For this purpose we extend our computational formalism of spin-orbit torques [10,11,12] to noncollinear magnets. An important problem in the formalism development concerns the correct inclusion of vertex corrections, without which several components of the current-induced torques in noncollinear chiral magnets would violate conservation laws. We will discuss the current-induced torques and spin-orbit driven effects that arise from the combination of structural inversion asymmetry, spin-orbit coupling, and noncollinear magnetism in Co/Pt and Mn/W bilayer systems. References: [1] K. Garello et al., Nature Nanotechnology 8, 587 (2013), [2] P. Wadley et al., Science 351, 587 (2016), [3] F. Freimuth et al., JPCM 26, 104202 (2014), [4] F. Freimuth et al., PRB 88, 214409 (2013), [5] F. Freimuth et al., JPCM 28, 316001 (2016), [6] F. Freimuth et al., ArXiv e-prints (2016), 1610.06541, [7] E. Jue et al., Nature Materials 15, 272 (2016), [8] L. Thomas et al., Nature Nanotechnology 8, 527 (2013), [9] S. Emori et al., Nature Materials 12, 611 (2013), [10] F. Freimuth et al., PRB 92, 064415 (2015), [11] F. Freimuth et al., PRB 90, 174423 (2014), [12] G. Geranton et al., PRB 91, 014417 (2015)
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