Unveiling Interfacial Spin-Orbit Torques in the Atomically Thin Limit: the Key Role of Skew Scattering
Aires Ferreira, University of York
July 28, 2020
Fueled by the discovery of ferromagnetism in 2D crystals in 2017, recent works have achieved spin-orbit torque (SOT) switching of ultra-thin van-der-Waals-bonded ferromagnets approaching the 2D limit . Conversely, nonmagnetic 2D crystals can be employed as an efficient source of nonequilibrium spin polarization . Experiments with atomically thin WTe2 demonstrated sought-after anti-damping SOT (ASOT) required for switching of perpendicular magnetization . While these early findings represent a stepping-stone towards envisaged all-electrical spin memories built entirely from 2D crystals , the driving force behind purely interfacial ASOT remains generally poorly understood.
In this talk I will argue that left-right scattering asymmetry plays a key, albeit hitherto neglected role in interfacial SOT. Starting from a unified theory of 2D crystal-ferromagnet interfaces, I will show that skew scattering generates a number of measurable effects (recently predicted in ), including: (i) a current-induced collinear spin polarization leading to sizeable ASOT and (ii) a non-equilibrium out-of-plane spin polarization which can be manipulated by controlling the current direction. Interestingly, the proposed Fermi surface mechanism is sensitive to sublattice-symmetry breaking and presence of impurity states near the Fermi level, resulting in a rich SOT phenomenology. Our accurate microscopic calculations indicate that the electrical torque efficiency can be tuned by up to 2 orders of magnitude by engineering the disorder landscape (e.g. by introduction of resonant impurities) . The skew scattering mechanism is operative in realistic devices and is expected to dominate the ASOT angular dependence in weakly disordered interfaces. Finally, I will briefly discuss the implications of these theoretical findings for our general understanding of emergent SOTs at heterointerfaces .
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