Magneto-Optical Detection of the Spin Hall Effect in Pt and W Thin Films

Abstract

The conversion of charge currents into spin currents in nonmagnetic conductors is a hallmark manifestation of spin-orbit coupling that has important implications for spintronic devices. Here we report the measurement of the interfacial spin accumulation induced by the spin Hall effect in Pt and W thin films using magneto-optical Kerr microscopy. We show that the Kerr rotation has opposite sign in Pt and W and scales linearly with current density. By comparing the experimental results with ab initio calculations of the spin Hall and magneto-optical Kerr effects, we quantitatively determine the current-induced spin accumulation at the Pt interface as 5×10^{-12} μ_{B} A^{-1} cm^{2} per atom. From thickness-dependent measurements, we determine the spin diffusion length in a single Pt film to be 11±3 nm, which is significantly larger compared to that of Pt adjacent to a magnetic layer.

Gigantic intrinsic orbital Hall effects in weakly spin-orbit coupled metals

“…In this case, we find that σ OH ≈ 2700 (h/e)(Ω · cm) −1 and σ SH ≈ 2000 (h/e)(Ω · cm) −1 for the true Fermi energy (horizontal dashed line). The large SHC in Pt is consistent with other theoretical calculations 11,13 and experimental results, 16,35 which verifies reliability of our calculation based on the TB model. Under gradual decrease of the orbital hybridization strength, we observe that both OHC and SHC monotonically decrease [ Fig.…”

X-ray spectroscopy of current-induced spin-orbit torques and spin accumulation in Pt/3d -transition-metal bilayers

“…Choosing a nonmagnetic layer in contact with Pt has the advantage of avoiding the direct interaction that the accumulated spins would have with the Co magnetic moment. This is apparent if one compares values of the spin diffusion length: whereas for a single Pt layer at room temperature up to 11 nm was found [5], this length is reduced to values between 1.1 [28] and 2 nm [25] if Pt is in contact with Co. Direct XMCD studies at the Pt L 3 , L 2 edges [29] would circumvent this difficulty, but the Pt L edges around 11.5 keV photon energy have a lower cross section and reduced XMCD contrast compared to the 3d transition metal edges, resulting in a sensitivity of ≈ 10 −3 µ B per Pt atom [30].…”

“…At our current density, one expects an accumulation of 1.3 × 10 −5 µ B at the surface of Pt, for thickness t P t ≫ λ P t = 11 nm. For the 10 nm Pt thickness used here, this value would be reduced to ≈ 4 × 10 −6 µ B using the correction for finite Pt thickness [24,25] but with the spin diffusion length of a single Pt layer [5] of λ P t = 11 nm. Experimentally we determined the moment in Cu to be lower than ≈ 3 × 10 −6 µ B for 10 nm Pt/Cu sample, which confirms that we are in the range of detecting the magnetic moment.…”

Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems

“…The magneto-optic Kerr effect (MOKE) allows for detecting the in-plane and out-of-plane components of the magnetization through the rotation of the light polarization upon reflection from a magnetic surface (Qiu and Bader, 2000). MOKE microscopy, with a wavelengthlimited resolution of about 1 µm, has been used extensively to characterize SOT-induced domain nucleation and displacement (Emori et al, 2013;Miron et al, 2010;Ryu et al, 2013;Safeer et al, 2016) as well as the currentinduced spin accumulation in bare Pt and W layers (Stamm et al, 2017). MOKE-based detection schemes have been used also to estimate the SOT amplitude by measuring the oscillations of the magnetization induced by an ac current in thin metal bilayers (Fan et al, 2014a).…”