Research ArticleMATERIALS SCIENCE

Dirac surface state–modulated spin dynamics in a ferrimagnetic insulator at room temperature

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Science Advances  01 Jun 2018:
Vol. 4, no. 6, eaas8660
DOI: 10.1126/sciadv.aas8660
  • Fig. 1 FMR measurement principle and TI properties.

    (A) Schematic drawing of magnetization dynamics in YIG interfaced with TI in which the spin of the surface state electron is locked to momentum. (B) Room temperature sheet resistance of (BixSb1−x)2Te3 with different Bi concentrations. (C) Temperature dependence of the sheet resistance of seven YIG (10 nm)/(BixSb1−x)2Te3 (five QLs) heterostructures.

  • Fig. 2 YIG FMR spectra with and without TI.

    (A) Definition of polar angles θH and θM, in FMR measurements. (B) FMR derivative absorption spectra of YIG/Sb2Te3 and YIG reference sample at a frequency of 9.6 GHz with magnetic field applied in-plane (θH = 90°). The solid lines are the best fits to extract the resonance field Hres and peak-to-peak linewidth ΔHpp. a.u., arbitrary units. (C) FMR derivative absorption spectra of YIG/Sb2Te3 and YIG reference sample with the polar angle θH ranging from 0° (out-of-plane) to 90° (in-plane) at 300 K. The extra peak-like feature on the high-field side of the resonance at 0° and 10° is also observed in some other samples, which could be caused by minor inhomogeneity change in YIG due to the presence of the TI layer.

  • Fig. 3 Extracted 4πMeff from FMR polar angle dependence fitting.

    (A) Polar angle θH dependence of FMR resonance field Hres for all seven YIG (10 nm)/(BixSb1−x)2Te3 (five QLs) samples and YIG reference sample. Solid curves are the best fits. (B) Bi concentration dependence of extracted effective anisotropy field 4πMeff obtained from fitting in (A) for all seven YIG (10 nm)/(BixSb1−x)2Te3 (five QLs) samples. The gray dashed line is the 4πMeff value for the YIG reference sample.

  • Fig. 4 Extracted Gilbert damping from FMR linewidth fitting.

    (A) FMR transmission spectra S21 for YIG/Sb2Te3 for different chosen frequencies: 4, 6, 8, 10, and 12 GHz at 300 K after background subtraction. (B) Normalized FMR spectra S21 at a fixed frequency of 10 GHz with an applied in-plane static field for YIG/(BixSb1−x)2Te3 samples with different Bi concentrations and YIG reference sample. (C) Frequency dependence of FMR linewidth for all seven YIG/TI samples and YIG reference sample. The resonance peak height is reduced in samples with increased damping constant, which causes poor Lorentzian fitting and, consequently, large apparent noise in extracted linewidth. (D) Bi concentration (x) dependence of the Gilbert damping constant α extracted from the slope of the straight lines in (C).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/6/eaas8660/DC1

    fig. S1. Crystal structure and surface morphology.

    fig. S2. FMR resonance field and linewidth for all YIG films.

    fig. S3. Effect of Pt on YIG resonance characteristics.

    fig. S4. Comparison of FMR between YIG/TI and YIG/Pt.

    fig. S5. Comparison of total effective anisotropy field and demagnetizing field.

    fig. S6. High-resolution transmission electron microscope image of a representative YIG/TI sample.

    fig. S7. TI surface state dispersion.

    fig. S8. Direct transition of TI conduction electrons driven by spin pumping.

    table S1. Two parameters (that is, 4πMeff and γ/2π) obtained from fitting.

    References (32, 33)

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Crystal structure and surface morphology.
    • fig. S2. FMR resonance field and linewidth for all YIG films.
    • fig. S3. Effect of Pt on YIG resonance characteristics.
    • fig. S4. Comparison of FMR between YIG/TI and YIG/Pt.
    • fig. S5. Comparison of total effective anisotropy field and demagnetizing field.
    • fig. S6. High-resolution transmission electron microscope image of a representative YIG/TI sample.
    • fig. S7. TI surface state dispersion.
    • fig. S8. Direct transition of TI conduction electrons driven by spin pumping.
    • table S1. Two parameters (that is, 4πMeff and γ/2π) obtained from fitting.
    • References (32, 33)

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