Research ArticleCONDENSED MATTER PHYSICS

Current-driven magnetization switching in ferromagnetic bulk Rashba semiconductor (Ge,Mn)Te

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Science Advances  07 Dec 2018:
Vol. 4, no. 12, eaat9989
DOI: 10.1126/sciadv.aat9989
  • Fig. 1 Rashba-Edelstein effect in ferromagnetic Rashba semiconductor (Ge,Mn)Te.

    (A) Crystal structure of (Ge,Mn)Te with polar broken inversion symmetry along [111] denoted as P. A unit cell of (Ge,Mn)Te is represented as red lines. (B) Rashba-type spin-polarized band (valence band) by opening the magnetization gap due to broken time-reversal symmetry by ferromagnetic order. Broken lines represent the band structure above the ferromagnetic transition temperature at which the magnetization gap is closed. (C) Principle of Edelstein effect: The application of electric field along the x direction causes the shift in Fermi surfaces (represented as Δkx), resulting in spin accumulation. The black solid and dotted lines represent the Fermi surfaces without and with the application of electric field, respectively. (D) Schematic illustration of magnetization switching in (Ge,Mn)Te caused by current-induced spin-orbit torque. (E) Top-view photograph of a Hall bar device and illustration of measurement configuration.

  • Fig. 2 Transport properties of (Ge,Mn)Te.

    (A) Magnetic field dependence of Hall resistivity Ryx for a 192-nm-thick (Ge,Mn)Te film at temperatures of T = 10 K (<TCFM; red) and 200 K (>TCFM; black); the ferromagnetic transition temperature TCFM is approximately 80 K [see (D)]. (B) Magnetic field dependence of anomalous Hall component in Hall conductivity σAHE at T = 10 K for (Ge,Mn)Te thin films with thicknesses of 22, 74, 144, and 192 nm. (C) Top: Ferromagnetic Rashba band structures with EF above (left) and within (right) the exchange gap. Bottom: Hole concentration (p) dependence of spontaneous anomalous Hall conductivity σAHES at T = 10 K for all the measured samples with different thicknesses and p values. The inset shows the p dependence of the Hall angle tanθH. (D) Temperature dependence of σAHES normalized by the value at the lowest temperature T = 2 K for the films with various thicknesses.

  • Fig. 3 Experimental observation of current-driven magnetization switching.

    (A) Variation in Hall resistivity ΔRyxpulse by current pulse injection for (Ge,Mn)Te thin films with thicknesses of 22, 74, 144, and 192 nm. Red and blue traces correspond to the cases of the in-plane bias magnetic field of +0.02 and −0.02 T, respectively, which are applied along the current direction (depicted in Fig. 1D). (B) Top: Schematic view of the EF shift in ferromagnetic Rashba bands and change in Fermi surface at EF. Bottom: Hole concentration (p) dependence of switching ratio of Hall resistivity defined as ΔRyxpulse/RAHES.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/12/eaat9989/DC1

    Section S1. Determination of lattice constants for (Ge,Mn)Te thin films by x-ray diffraction

    Section S2. Qualitative evaluation of EF in (Ge,Mn)Te

    Section S3. Electronic transport properties of the (Ge,Mn)Te samples

    Section S4. Temperature dependence of Hall resistivity

    Section S5. Current-induced magnetization reversal for all samples

    Section S6. Current-directional dependence of magnetization switching

    Section S7. In-plane bias magnetic field dependence of magnetization switching

    Section S8. Repeated injection of pulses lower than saturation current density

    Section S9. The estimation of spin Hall efficiency

    Section S10. Correction of current flow to buffer layers

    Section S11. Magnetization measurement

    Fig. S1. Reciprocal space analysis for the in- and out-of-plane lattice constants of (Ge,Mn)Te thin film.

    Fig. S2. Calculated band structure of (Ge,Mn)Te for x = 0.08.

    Fig. S3. Transport properties for all samples.

    Fig. S4. Temperature dependence of Hall resistivity.

    Fig. S5. Current-induced magnetization for all samples.

    Fig. S6. Current-directional dependence of magnetization switching.

    Fig. S7. In-plane bias magnetic field dependence of magnetization switching.

    Fig. S8. Repeated injection of pulses lower than saturation current density.

    Fig. S9. Second-harmonic Hall resistivity.

    Fig. S10. Temperature dependence of resistivity of the GeTe/Sb2Te3 thin film.

    Fig. S11. Magnetization measurement for 74- and 192-nm-thick samples.

    Table S1. Physical parameters for the effective band model of (Ge,Mn)Te.

    Table S2. Current ratio for all samples.

    References (3941)

  • Supplementary Materials

    This PDF file includes:

    • Section S1. Determination of lattice constants for (Ge,Mn)Te thin films by x-ray diffraction
    • Section S2. Qualitative evaluation of EF in (Ge,Mn)Te
    • Section S3. Electronic transport properties of the (Ge,Mn)Te samples
    • Section S4. Temperature dependence of Hall resistivity
    • Section S5. Current-induced magnetization reversal for all samples
    • Section S6. Current-directional dependence of magnetization switching
    • Section S7. In-plane bias magnetic field dependence of magnetization switching
    • Section S8. Repeated injection of pulses lower than saturation current density
    • Section S9. The estimation of spin Hall efficiency
    • Section S10. Correction of current flow to buffer layers
    • Section S11. Magnetization measurement
    • Fig. S1. Reciprocal space analysis for the in- and out-of-plane lattice constants of (Ge,Mn)Te thin film.
    • Fig. S2. Calculated band structure of (Ge,Mn)Te for x = 0.08.
    • Fig. S3. Transport properties for all samples.
    • Fig. S4. Temperature dependence of Hall resistivity.
    • Fig. S5. Current-induced magnetization for all samples.
    • Fig. S6. Current-directional dependence of magnetization switching.
    • Fig. S7. In-plane bias magnetic field dependence of magnetization switching.
    • Fig. S8. Repeated injection of pulses lower than saturation current density.
    • Fig. S9. Second-harmonic Hall resistivity.
    • Fig. S10. Temperature dependence of resistivity of the GeTe/Sb2Te3 thin film.
    • Fig. S11. Magnetization measurement for 74- and 192-nm-thick samples.
    • Table S1. Physical parameters for the effective band model of (Ge,Mn)Te.
    • Table S2. Current ratio for all samples.
    • References (3941)

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