Abstract
The efficient conversion of spin to charge transport and vice versa is of major relevance for the detection and generation of spin currents in spin-based electronics. Interfaces of heterostructures are known to have a marked impact on this process. Here, terahertz (THz) emission spectroscopy is used to study ultrafast spin-to-charge-current conversion (S2C) in about 50 prototypical F|N bilayers consisting of a ferromagnetic layer F (e.g., Ni81 Fe19 , Co, or Fe) and a nonmagnetic layer N with strong (Pt) or weak (Cu and Al) spin-orbit coupling. Varying the structure of the F/N interface leads to a drastic change in the amplitude and even inversion of the polarity of the THz charge current. Remarkably, when N is a material with small spin Hall angle, a dominant interface contribution to the ultrafast charge current is found. Its magnitude amounts to as much as about 20% of that found in the F|Pt reference sample. Symmetry arguments and first-principles calculations strongly suggest that the interfacial S2C arises from skew scattering of spin-polarized electrons at interface imperfections. The results highlight the potential of skew scattering for interfacial S2C and propose a promising route to enhanced S2C by tailored interfaces at all frequencies from DC to terahertz.
Highlights
The efficient conversion of spin to charge transport and vice versa is of major relevance for the detection and generation of spin currents in spinbased electronics
A generic structure for studying such spin-to-charge-current conversion (S2C) is the prototypical bilayer of Figure 1a: A spin current with electron-number density js flowing along the z direction is converted into a transverse charge current with density jc
Major S2C effects are the inverse spin Hall effect (ISHE)[2] in nonmagnetic materials and ferro- or ferrimagnets and the inverse Rashba–Edelstein effect (IREE),[5,6] the latter only occurring in regions with broken inversion symmetry like interfaces
Summary
Www.advmat.de of the F–N interfacial S2C contribution. We did, not attempt to compare the signs of measured THz charge currents and calculated SHAs for all samples for two reasons. They show that interfacial contributions to S2C need to be considered before the measured magnetization-dependent transverse charge current is assigned exclusively to bulk effects in the F or N layer. The skew scattering off Cu(Py) interfacial imperfections (Figure 6b) is enhanced by the relatively long relaxation length (λPy/Cu ≈ 1.9 nm) of the ballistically propagating electrons in the Cu layer (Figure S9, Supporting Information). This remarkable nonlocal mechanism opens up a promising route to enhancing S2C by controlling the structure of the spintronic interface
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