Research ArticleMATERIALS SCIENCE

Potential energy–driven spin manipulation via a controllable hydrogen ligand

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Science Advances  14 Apr 2017:
Vol. 3, no. 4, e1602060
DOI: 10.1126/sciadv.1602060
  • Fig. 1 Influence of hydrogen-functionalized tips on imaging and spectroscopy.

    (A) Constant current STM image (approximately 5 × 5 nm2; V = −15 mV, I = 20 pA, G = 1.72 × 10−5 G0) of CoH complexes on the h-BN/Rh(111) moiré obtained with a hydrogen-functionalized tip. Areas with enhanced contrast due to hydrogen in the junction are circled in red. (B) Constant current STM images (1.2 × 1.2 nm2; top to bottom: V = −0.3, −0.7, −1.0, −1.3, and −1.6 mV; I = 20 pA, corresponding to G = 8.60 × 10−4, 3.69 × 10−4, 2.58 × 10−4, 1.99 × 10−4, and 1.61 × 10−4 G0) of a CoH complex highlighting the strong conductance (tip-sample distance) dependence of imaging with a hydrogen-functionalized tip. (C) Local spectroscopy obtained on the CoH complex in (B). The tip was centered on the bright lobe (G = 1.61 × 10−4 G0). At G = 6.45 × 10−4 G0 (blue), a set of double steps is observed, indicative of a spin 1 complex with magnetic anisotropy. Increasing the conductance in steps of ΔG = 0.16 × 10−4 G0 leads to unstable spectra until a spin 1/2 Kondo peak emerges at high conductance (red; G = 12.9 × 10−4 G0). All spectra are normalized to the differential conductance at −10 mV; normalized spectra are offset by 0.5. arb. units, arbitrary units.

  • Fig. 2 Conductance-distance spectroscopy.

    (A) Conductance-distance, G(z), curves obtained with a bare Pt tip on h-BN (black), CoH (dashed blue), and CoH2 (dotted yellow) at a tip-sample bias of V= −10 mV. (B) Using a functionalized tip, CoH + Htip (red), a conductance discontinuity, corresponding to the S = 1 to S = 1/2 total spin change, is observed at a relative height z of 70 pm. The functionalized tip approaching the substrate, h-BN + Htip (dashed green), shows no discontinuity and has a nonexponential character. For direct comparison, the CoH G(z) measurement from (A) is plotted again (dashed blue). Inverse decay constants, κG: (A) h-BN (black), 8.7 ± 0.1 nm−1; CoH (dashed blue), 9.9 ± 0.1 nm−1; CoH2 (dotted yellow), 9.8 ± 0.1 nm−1; (B) h-BN + Htip (dashed green), 6.6 ± 0.3 nm−1 (0 < z < 70 pm) and 7.7 ± 0.4 nm−1 (70 pm < z < 200 pm); CoH + Htip (red), 6.9 ± 0.4 nm−1 (0 < z < 70 pm) and 8.5 ± 0.5 nm−1 (70 pm < z < 200 pm). The color-coded insets schematically depict the junction geometry. (C) Plots of majority (left) and minority (right) spin-projected density of states (blue, d orbitals; red, sp orbitals) of an S = 1 CoH complex. The first plot shows a magnetic moment of 2.0 μB (without tip) (i), the second plot shows a slight magnetic moment reduction (1.6 μB) due to the presence of a hydrogen-functionalized tip (ii), and the third plot shows the transition from S = 1 to S = 1/2 (1.2 μB) at close tip distances (iii). The change in Stoner splitting between majority and minority bands is schematically depicted with vertical gray arrows.

  • Fig. 3 Force measurements on a switching complex.

    (A) Simultaneous frequency shift–distance [Δf(z) (black)] and conductance-distance [G(z) (gray)] measurements at V = −10 mV on a CoH S = 1 complex with hydrogen-functionalized tip. The spin transition, occurring at a relative height z of 50 pm, is evident in both force and conductance channels. (B) Frequency shift was converted to short-range forces (black), and the conductance was deconvoluted to remove averaging over the oscillation amplitude (gray). On either side of the transition region, the deconvoluted conductance (Deconv. cond.) and force increase exponentially and can be described by the expressions G(z′) = G0exp(−2κG(z0 + z′)) and F(z′) = F0exp(−2κF(z0 + z′)), respectively. Inverse decay constants: κG, 13.0 ± 0.5 nm−1 (0 < z′ < 30 pm) and 9.5 ± 0.1 nm−1 (70 < z′ < 200 pm); κF, 10.0 ± 0.5 nm−1 (0 < z′ < 30 pm) and 4.2 ± 0.3 nm−1 (70 < z′ < 200 pm). (C) Interaction potential energy surface during the S = 1 to S = 1/2 transition (black), determined by integrating the experimental F(z′) data. Dashed lines highlight the change in slope and indicate the point where a lower potential energy surface becomes accessible. Vertical dotted lines in (B) and (C) indicate the transition regime. For all curves, zero distance corresponds to the point of closest approach. (D) Simulated diabatic potential energy curves for a CoH/h-BN/Rh(111) complex approached by a hydrogen-functionalized Pt tip (blue dash-dotted curve) and a CoH2 approached with a bare tip (red dash-dotted curve). The approximate adiabatic curve is shown as the gray dotted line. The reaction coordinate dCo-Pt is the distance between the Co and the apex Pt atoms.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/4/e1602060/DC1

    fig. S1. Reversibility of the switching process.

    fig. S2. Bias- and polarity-dependent Δf(z) curves.

    fig. S3. Long-range background subtraction.

    fig. S4. Schematic drawing of the simulated junction geometry.

    fig. S5. Measured dissipation across the spin transition.

    fig. S6. Calculated magnetic moment as a function of Co-Pt separation.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Reversibility of the switching process.
    • fig. S2. Bias- and polarity-dependent Δf(z) curves.
    • fig. S3. Long-range background subtraction.
    • fig. S4. Schematic drawing of the simulated junction geometry.
    • fig. S5. Measured dissipation across the spin transition.
    • fig. S6. Calculated magnetic moment as a function of Co-Pt separation.

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