Quantitative study of the spin Hall magnetoresistance in ferromagnetic insulator/normal metal hybrids

Abstract

We experimentally investigate and quantitatively analyze the spin Hall magnetoresistance effect in ferromagnetic insulator/platinum and ferromagnetic insulator/nonferromagnetic metal/platinum hybrid structures. For the ferromagnetic insulator, we use either yttrium iron garnet, nickel ferrite, or magnetite and for the nonferromagnet, copper or gold. The spin Hall magnetoresistance effect is theoretically ascribed to the combined action of spin Hall and inverse spin Hall effect in the platinum metal top layer. It therefore should characteristically depend upon the orientation of the magnetization in the adjacent ferromagnet and prevail even if an additional, nonferromagnetic metal layer is inserted between Pt and the ferromagnet. Our experimental data corroborate these theoretical conjectures. Using the spin Hall magnetoresistance theory to analyze our data, we extract the spin Hall angle and the spin diffusion length in platinum. For a spin-mixing conductance of 4 × 10 14 −1 m −2 , we obtain a spin Hall angle of 0.11 ± 0.08 and a spin diffusion length of (1.5 ± 0.5) nm for Pt in our thin-film samples.

Spin-Hall magnetoresistance in platinum on yttrium iron garnet: Dependence on platinum thickness and in-plane/out-of-plane magnetization

“…For both fitted curves, an assumed linear background resistance, as indicated by the dotted red line, is also added. The derived fits are in good agreement with the measured data for applied fields below the saturation field, which confirms the presence of SMR and its dependence on the magnetization direction, 12,22,23 also for out-of-plane applied fields.…”

Current-induced spin torque resonance of a magnetic insulator

“…The resistivity of the Pt films varies within the margin expected from earlier measurements [30]. In very thin films we routinely observe a variation of the resistivity by a factor of 2 due to surface termination, ambient pressure, and other growth related variables.…”

“…Subsequently the Pt layer was deposited in situ, without breaking the vacuum, on the YIG thin film by electron-beam evaporation [30]. The resistivity of the Pt films varies within the margin expected from earlier measurements [30].…”

“…We find that the excitation in this sample is dominated by the Oersted field as expected for the comparably large YIG layer thickness. The largely symmetric shape of the resonance peak is due to a significant spin pumping contribution, with SMR being small ( ρ/ρ ≈ 2 × 10 −4 ) [19,30] for thick Pt films.…”

“…The spin transport parameters are spin diffusion length λ = 1.5 nm, spin Hall angle θ SH = 0.11, and spin mixing conductance Re(G ↑↓ ) = 4 × 10 14 −1 m −2 , which have proven to be robust to variations of other sample parameters (Refs. [30,32]). The phase δ = −63 • is inferred from additional measurements with magnetic fields oriented at a slight angle to the film normal (see Sec.…”