Research ArticleAPPLIED PHYSICS

Spin-charge conversion in NiMnSb Heusler alloy films

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Science Advances  13 Dec 2019:
Vol. 5, no. 12, eaaw9337
DOI: 10.1126/sciadv.aaw9337
  • Fig. 1 Schematic illustrations for the NiMnSb crystal and electronic band structures.

    (A) Crystal structure of NiMnSb in the C1b phase. (B) Half-metallic band structure in NiMnSb. The minority band gap closes because of the interaction between electrons and magnons, i.e., the right-hand side illustration of bulk state. The minority band state exists at the interface/surface (Inter./Sur.). (C) Spin-charge conversion with interface and bulk contributions. Here, JInter.Sur.S and JBulkS represent the spin currents due to interface/surface and bulk, respectively. JTotalC indicates the converted total charge current.

  • Fig. 2 Structural properties of NiMnSb films and AMR effect in the films.

    (A) Out-of-plane XRD patterns for 20-nm-thick NiMnSb films with two different ordering structures. (B) AMR effect for the two kinds of NiMnSb films measured by an in-plane ϕ scan method at a magnetic field of 2 T at 10 and 300 K, respectively.

  • Fig. 3 Voltage measurement with spin pumping.

    (A) Schematic illustration of the YIG/NiMnSb sample with experiment setup carried out in the study. (B) Magnetic field dependence of the electronic voltage, V, measured at 10 and 300 K. The directions of external magnetic field, Hex, are also indicated by the inset illustrations. The blue and red solid lines are fitting results for the experimental data by Eq. 1. (C) FMR spectra in YIG (left) and voltage signals in NiMnSb (right) measured in the temperature range from 10 to 300 K. The applied microwave power and frequency here are 25 mW and 5 GHz, respectively.

  • Fig. 4 Temperature dependence of VSC with varying microwave power, microwave frequency, and NiMnSb thickness.

    (A) VSC as a function of temperature measured at different microwave powers of Pin = 50, 100, and 200 mW, with the microwave frequency of f = 5 GHz. (B) VSC as a function of temperature at different microwave frequencies of f = 5, 6, and 7 GHz with the microwave power of Pin = 25 mW. (C) Temperature dependence of VSC divided by the amplitude of FMR absorption of YIG for NiMnSb films with the thickness of 10, 20, 30, and 50 nm. The VSC measured in a less-ordered NiMnSb film with the thickness of 20 nm is also shown for comparison. The microwave condition is Pin = 25 mW and f = 5 GHz. (D) The dependence of cross temperature, Tcross, for the sign change of VSC on NiMnSb thickness, t. The inset is an enlarged view of (C) in the temperature region below 100 K.

  • Fig. 5 Sketch of the voltage due to spin-charge conversion as a function of temperature.

    There are two thicknesses, d1 (blue) and d2 (red) (d2 > d1), with the crossing temperatures T1 and T2 (T2 > T1), respectively. The green dashed line is the interfacial contribution V0.

  • Fig. 6 Resistivity of NiMnSb films and the voltage due to spin-charge conversion as a function of temperature.

    (A) The dependence of the resistivity on temperature for the NiMnSb films with d = 10, 20, 30, and 50 nm. The linear T dependence (~γT) in the high-temperature regime is indicated by a dash-dotted line with the respective value of γ for each thickness. (B) The voltage signal divided by the amplitude of FMR absorption of YIG against the temperature for the various thicknesses of the NiMnSb layer. The symbols represent the experimental data, and the solid line shows their fitted curve with the use of Eq. 9, with V0/PFMR = −0.02 μV/mW, respectively. The shaded areas show the range of fitting curves for −0.03 μV/mW < V0/PFMR < −0.01 μV/mW.

  • Table 1 Spin diffusion length and ratio σsH*/σsHss,0.

    The spin diffusion length at room temperature (300 K) and the ratio σsH*/σsHss,0 for the various thicknesses of the NiMnSb films are obtained by the fit of Eq. 9 to the experimental data as shown in Fig. 6B for V0/PFMR = −0.03, −0.02, and −0.01 μV/mW from left to right. Note that σsH* is temperature independent by definition and that σsHss,0 denotes the zero-temperature value of the skew scattering contribution.

    dλsd (300 K) (nm)σsH*/σsHss,0
    50 nm9.4714.0319.65−0.16−0.27−0.29
    30 nm4.746.328.310.09−0.05−0.12
    20 nm4.215.487.27−0.23−0.32−0.39
    10 nm2.823.073.37−0.60−0.62−0.63

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/12/eaaw9337/DC1

    Section S1. Experimental results on the FMR spectrum of NiMnSb and the voltage signals due to the NiMnSb resonance and angular dependence of voltage signal by spin-charge conversion

    Section S2. Technical details of the theory of the voltage due to spin-charge conversion

    Fig. S1. Typical FMR spectra and voltage signals in the YIG/NiMnSb (20 nm) sample.

    Fig. S2. Angular dependence of voltage signal by spin-charge conversion.

    References (5458)

  • Supplementary Materials

    This PDF file includes:

    • Section S1. Experimental results on the FMR spectrum of NiMnSb and the voltage signals due to the NiMnSb resonance and angular dependence of voltage signal by spin-charge conversion
    • Section S2. Technical details of the theory of the voltage due to spin-charge conversion
    • Fig. S1. Typical FMR spectra and voltage signals in the YIG/NiMnSb (20 nm) sample.
    • Fig. S2. Angular dependence of voltage signal by spin-charge conversion.
    • References (5458)

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