Research ArticleCONDENSED MATTER PHYSICS

Variation of the giant intrinsic spin Hall conductivity of Pt with carrier lifetime

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Science Advances  19 Jul 2019:
Vol. 5, no. 7, eaav8025
DOI: 10.1126/sciadv.aav8025
  • Fig. 1 Sample structure.

    (A) Schematic of enhanced impurity scattering in Pt by finely dispersed MgO molecules. (B) XPS spectrum for Pt 4f peaks in a Pt0.6(MgO)0.4 layer (black line) and a pure Pt layer (red line), indicating non-oxidation of Pt in both cases. a.u., arbitrary units. (C) XPS spectrum for Pt 4d and 4p peaks, Mg KLL peak, and O 1s, indicating that Pt atoms are not oxidized while Mg and O atoms coexist as MgO molecules in the Pt1−x(MgO)x layer peak. The solid lines represent the peak positions expected for nonbonding instances. Different from the Pt peaks, the Mg KLL and O 1s peaks show clear shifts of ±0.8 eV in binding energy, suggesting that Pt is not oxidized while Mg is oxidized. (D) Cross-sectional high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) image and energy-dispersive x-ray spectroscopy mapping of Pt, Mg, and O, showing no indication of Pt or MgO clusters. The two dotted lines represent the upper and lower interfaces of the Pt0.6(MgO)0.4 layer. (E) Cross-sectional high-resolution transmission electron microscopy image (bright field) of a magnetic stack of Ta 1/ Pt0.6(MgO)0.4 4/Co 1.4/MgO 2/TaOx 1.5. (F) XRD θ-2θ patterns for Pt1−x(MgO)x/Co bilayers with different x, indicating the robustness of the long-range fcc order of Pt (peak position) in the presence of increasing MgO impurities (peak weakening and broadening).

  • Fig. 2 Variation of the SHC with carrier lifetime.

    The experimental values of (A) the average resistivity, (B) carrier lifetime, (C) the apparent SHC (σSH*) for Pt1−x(MgO)x 4/Co 1.4 bilayers plotted as a function of MgO concentration (x) of the Pt1−x(MgO)x layers. (D) Experimental and theoretical values for the (apparent) SHC of Pt plotted as a function of σxx/(1 − x), with σxx/(1 − x) being an approximate linear indicator of carrier lifetime. Inset: Nonlinear dependence of the experimental values of σSH* and σSH on σxx. In (D), the black dots, gray squares, and violet dot represent σSH of Pt predicted by the tight-binding model and first-principles calculations in the studies of Tanaka et al. (1), Guo et al. (2), and Obstbaum et al. (18), respectively. The red star represents the experimental value of σSH of Pt determined in (31). The dashed lines in (D) are solely to guide the eyes.

  • Fig. 3 Spin Hall ratio, damping-like SOT efficiency, and current-induced switching of perpendicular magnetization.

    (A) The MgO concentration dependence of θSH and ξDLj for the Pt1−x(MgO)x 4/Co 1.4 bilayers. (B) VAH versus I (Hx = −1500 Oe), (C) VAH versus I (Hx = 1500 Oe), (D) VAH versus Hz, and (E) VAH versus Hx for the Pt0.7(MgO)0.3 4/Co 0.68 bilayers. The Hall bar dimension is 5 μm by 60 μm. The applied electric field is E = 1.67 kV/m for (B) to (E).

  • Table 1 Comparison of ξDLj, θ, ρxx, σSH*(x) and calculated power and current consumption of SOT-MRAM devices for various strong spin current generators.

    Here, we use a spin Hall channel (600 nm by 300 nm by 4 nm), an FeCoB free layer (190 nm by 30 nm by 1.8 nm; resistivity ≈ 130 microhm·cm), and the parallel resistor model for the illustrative calculation (see the Supplementary Materials for details on the power and current calculations). Power and current are normalized to that of the Pt0.6(MgO)0.4-based device. n.a., not applicable.

    ξDLjθSHρxx
    (microhm·cm)
    σSH
    [105 (ℏ/2e) ohm−1 m−1]
    PowerCurrentReference
    Pt0.6(MgO)0.40.28>0.73743.81.01.0This work
    Pd0.25Pt0.750.26>0.6584.50.91.0(14)
    Au0.25Pt0.750.3>0.6833.61.00.95(16)
    Pt0.160.51334.91.21.6This work
    Bi2Se33.5n.a.17552.02.60.3(46)
    Pt0.5(MgO)0.50.310.662401.34.51.2This work
    β-W0.3n.a.3001.07.11.3(43)
    β-Ta0.12n.a.1900.63212.8(44)
    BixSe1−x18.6n.a.130001.4250.4(47)

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/7/eaav8025/DC1

    Fig. S1. Evolution of SHC with carrier lifetime.

    Fig. S2. Three carrier scattering schemes.

    Fig. S3. Composition dependence of the intensity and the full width at half maximum of the XRD patterns.

    Fig. S4. Determination of SOT effective fields.

    Fig. S5. MgO concentration dependence of spin-torque fields, spin diffusion length, and interfacial spin transparency.

    Fig. S6. Enhancement of the spin Hall ratio in Pt by shortening carrier lifetime.

    Fig. S7. MgO concentration dependence of interfacial magnetic anisotropy energy density.

    Fig. S8. Temperature dependence of resistivity for 4-nm-thick Pt and Pt0.6(MgO)0.4 films.

    Fig. S9. Schematics of a SOT-MRAM device.

    Section S1. In-plane harmonic response measurements

    Section S2. Calculation of power consumption of SOT-MRAM devices

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Evolution of SHC with carrier lifetime.
    • Fig. S2. Three carrier scattering schemes.
    • Fig. S3. Composition dependence of the intensity and the full width at half maximum of the XRD patterns.
    • Fig. S4. Determination of SOT effective fields.
    • Fig. S5. MgO concentration dependence of spin-torque fields, spin diffusion length, and interfacial spin transparency.
    • Fig. S6. Enhancement of the spin Hall ratio in Pt by shortening carrier lifetime.
    • Fig. S7. MgO concentration dependence of interfacial magnetic anisotropy energy density.
    • Fig. S8. Temperature dependence of resistivity for 4-nm-thick Pt and Pt0.6(MgO)0.4 films.
    • Fig. S9. Schematics of a SOT-MRAM device.
    • Section S1. In-plane harmonic response measurements
    • Section S2. Calculation of power consumption of SOT-MRAM devices

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