Research ArticlePHYSICS

Molecular engineering of Rashba spin-charge converter

See allHide authors and affiliations

Science Advances  23 Mar 2018:
Vol. 4, no. 3, eaar3899
DOI: 10.1126/sciadv.aar3899
  • Fig. 1 Rashba spin-orbit device decorated with SAMs.

    (A) Fermi contours of a Rashba system under an external electric field. A shift of the Fermi circles gives rise to a spin polarization. (B) Schematic illustration of the REMR in a Bi/Ag/CoFeB trilayer induced by the Rashba-Edelstein effect at the Bi/Ag interface. (C) The static water contact angles θs of the Bi/Ag/CoFeB trilayers measured by putting 1.5 μl of a water droplet on the surface. (D) Square root of photoelectron emission yield as a function of scan energy measured with an atmospheric photoelectron spectrometer for the pristine Bi/Ag/CoFeB trilayer (black), Bi/Ag/CoFeB trilayer decorated with ODT (blue), and Bi/Ag/CoFeB trilayer decorated with PFDT (red). The solid lines are linear fits, from which the baseline intercept gives the work function of the trilayers. (E) Schematic illustration of ODT and PFDT molecules on the Bi surface. The arrows represent the dipole moment of the SAM-forming molecules obtained from DFT calculations.

  • Fig. 2 Rashba-Edelstein MR.

    The change in the longitudinal resistance, ΔR, of (A) the Bi(5 nm)/Ag(2 nm)/CoFeB(2.5 nm) trilayer, (B) ODT–Bi(5 nm)/Ag(2 nm)/CoFeB(2.5 nm) trilayer, and (C) PFDT–Bi(5 nm)/Ag(2 nm)/CoFeB(2.5 nm) trilayer, as a function of the rotation of the magnetic field of 6 T, where R is the longitudinal resistance at μ0H = 0. The rotation angles (α, β, and γ) are defined in (D). The schematic illustrations of the pristine Bi/Ag/CoFeB trilayer and SAM-decorated Bi/Ag/CoFeB trilayers are also shown. The schematic illustrations of the SAMs were drawn based on the literature (39), where an n-alkyl thiol molecule forms SAM tilted from the surface normal by 20° to 30 °. Although this case is for SAM on gold, DFT and AM1 calculations have shown that the molecular configuration on bismuth is similar to that on gold (40).

  • Fig. 3 Spin pumping and inverse Rashba-Edelstein effect.

    Magnetic field μ0H dependence of the charge current Jc, derived from the dc electric voltage, for the (A) Ag(2.5 nm)/Ni81Fe19(6 nm), (B) Bi(5 nm)/Ag(2.5 nm)/Ni81Fe19(6 nm), (C) ODT–Bi(5 nm)/Ag(2.5 nm)/Ni81Fe19(6 nm), and (D) PFDT–Bi(5 nm)/Ag(2.5 nm)/Ni81Fe19(6 nm) films measured by applying a 200-mW microwave, where μ0HFMR is the FMR field. The solid circles are the experimental data, and the solid curves are the fitting result using a combination of symmetric and antisymmetric functions. The symmetric and antisymmetric components of the fitting results are plotted correspondingly.

  • Fig. 4 Phototuning of REMR.

    (A) Illustration of the reversible cis-trans photoisomerization of AZ-SAM formed on the Bi/Ag/CoFeB trilayer under the UV and visible light irradiation. The arrows represent the dipole moment of AZ obtained from DFT calculations. (B) Change in the REMR ratio ΔMR = MR − MRavg obtained from the ADMR for the AZ-SAM–decorated Bi/Ag/CoFeB trilayer measured after the visible (N = 1, 3, 5) or UV (N = 2, 4) light irradiation. Here, MR ≡ [ΔR(β = 0) − ΔR(β = 90°)]/R, where N represents the cycle index. MRavg is the average MR for N = 1, 2, 3, 4, 5. (C) REMR ratio for the pristine Bi/Ag/CoFeB trilayer measured after the visible (N = 1, 3, 5) or UV (N = 2, 4) light irradiation. (D) Static water contact angle θs for the AZ-SAM–decorated Bi/Ag/CoFeB trilayer measured after the visible (N = 1, 3, 5) or UV (N = 2, 4) light irradiation.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/3/eaar3899/DC1

    section S1. Atomic force microscopy

    section S2. Infrared reflection-absorption spectroscopy

    section S3. Field ADMR in SAM-decorated Bi/CoFeB bilayers

    section S4. Field strength dependence of MR in SAM-decorated Bi/Ag/CoFeB trilayers

    section S5. Charge transfer at organic-inorganic interface

    fig. S1. AFM images of the Bi/Ag/CoFeB trilayer and SAM-decorated Bi/Ag/CoFeB trilayers.

    fig. S2. IRRAS spectra of SAM-decorated Bi/Ag/CoFeB trilayers and infrared absorption spectra of bulk materials.

    fig. S3. Field ADMR in SAM-decorated Bi/CoFeB bilayers.

    fig. S4. Charge transfer at organic-inorganic interface.

    table S1. Field strength dependence of MR.

  • Supplementary Materials

    This PDF file includes:

    • section S1. Atomic force microscopy
    • section S2. Infrared reflection-absorption spectroscopy
    • section S3. Field ADMR in SAM-decorated Bi/CoFeB bilayers
    • section S4. Field strength dependence of MR in SAM-decorated Bi/Ag/CoFeB trilayers
    • section S5. Charge transfer at organic-inorganic interface
    • fig. S1. AFM images of the Bi/Ag/CoFeB trilayer and SAM-decorated Bi/Ag/CoFeB trilayers.
    • fig. S2. IRRAS spectra of SAM-decorated Bi/Ag/CoFeB trilayers and infrared absorption spectra of bulk materials.
    • fig. S3. Field ADMR in SAM-decorated Bi/CoFeB bilayers.
    • fig. S4. Charge transfer at organic-inorganic interface.
    • table S1. Field strength dependence of MR.

    Download PDF

    Files in this Data Supplement:

Navigate This Article