Research ArticleAPPLIED PHYSICS

Current-induced magnetization switching using an electrically insulating spin-torque generator

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Science Advances  23 Feb 2018:
Vol. 4, no. 2, eaar2250
DOI: 10.1126/sciadv.aar2250
  • Fig. 1 Current-induced magnetization switching.

    (A) Schematic of the MgO/CoTb/Pt(O) heterostructure used for the AHE measurements. The charge current Idc and external magnetic field were applied along the x axis for magnetization switching. (B) The anomalous Hall effect (AHE) resistance RH measured by varying the perpendicular magnetic field μ0Hz for the MgO/CoTb/Pt(O) device. (C) Current-induced magnetization switching curves for the MgO/CoTb/Pt(O) heterostructure measured with different in-plane external magnetic fields μ0Hx. (D) Switching phase diagram for the MgO/CoTb/Pt(O) heterostructure, where Ic is the switching current.

  • Fig. 2 ST-FMR measurements.

    (A) Schematic of the SiO2/Ni81Fe19/Pt(O) device for the ST-FMR measurements. (B) ST-FMR spectra for the SiO2/Ni81Fe19/Pt(O) devices by changing the rf current frequencies from 4 to 10 GHz, where Q = 0 and 10%. (C) ST-FMR spectra for the SiO2/Ni81Fe19/Pt(O) devices at 7 GHz by changing Q from 0 to 35%. The solid circles are the experimental data and the solid curves are the fitting result using Eq. 1. The rf power of 24.7 dBm was applied for all the measurements. (D) The ST-FMR spectrum for the SiO2/Ni81Fe19 device at 7 GHz. (E) Q dependence of the magnetic damping constant α, obtained from the rf f dependence of the ST-FMR spectral width W using W = (2πα/γ)f + Wext, where γ is the gyromagnetic ratio and Wext is the extrinsic contribution to the spectral width. (F) Q dependence of the electrical resistivity ρ of Pt(O) films. The blue solid circle shows the electrical resistivity of a Ni81Fe19 film.

  • Fig. 3 Thickness dependence of ST-FMR.

    ST-FMR spectra for the SiO2/Ni81Fe19/Pt(O) devices at 7 GHz when Q is (A) 0 and (B) 10%. The Ni81Fe19- layer thickness dF was changed from 4 to 8 nm. (C) Inverse of the FMR spin-torque generation efficiency 1/ξFMR as a function of 1/dF for Q = 0, 4, 8, and 10%. The solid circles are the experimental data and the solid lines are the linear fit to the data.

  • Fig. 4 Spin-torque generation efficiencies when Q is less than 10%.

    (A) Q dependence of the damping-like ξDL and field-like ξFL spin-torque generation efficiencies. (B) Pt(O) layer resistivity ρ dependence of ξDL and ξFL. (C) Q dependence of the ratio between ξFL and ξDL. (D) Pt(O) layer resistivity ρ dependence of the ratio between ξFL and ξDL.

  • Fig. 5 Spin-torque generation efficiencies when Q is greater than 16%.

    (A) Pt(O) layer thickness dN dependence of the ST-FMR spectra for the SiO2/Ni81Fe19/Pt(O) devices at 7 GHz with Q = 20%. (B) Q dependence of the ratio between the damping-like HDL and field-like HFL effective fields. (C) Pt(O) layer resistivity ρ dependence of the ratio between HDL and HFL. (D) The change of the linewidth W(Idc) of the ST-FMR spectrum as a function of the applied dc current Idc for different Q. (E) Q dependence of Embedded Image and Embedded Image. (F) ρ dependence of Embedded Image and Embedded Image.

  • Fig. 6 Spin-torque generation controlled by O2− migration.

    (A) Schematic of the heterostructure used for O2− migration and ST-FMR measurement. The gray solid circles represent oxygen ions. (B) Typical ST-FMR spectra measured after removing the applied voltages of ± 35 V. The solid circles are the experimental data and the solid curves are the fitting result using Eq. 1. The offset of the curves in the vertical direction was shifted for comparison. (C) The magnitude of the S/A ratio obtained by fitting the corresponding ST-FMR spectra, where N represents the cycle index. The ST-FMR was measured for the Ni81Fe19/Pt(O)/Pt device after the application of a gate voltage of + 35 V (N = 1, 3, 5, and 7) or −35 V (N = 2, 4, 6, and 8). The in-plane electrical resistance R of the Ni81Fe19 layer in the Ni81Fe19/PtOx/PtOy/Pt device measured after removing the applied voltages of ± 35 V is plotted correspondingly. (D) Schematic of the experimental setup for the application of the gate voltages used to drive O2− migration. O2− migrates toward the Ni81Fe19/Pt(O) interface for the application of the positive gate voltage (left), whereas the negative gate voltage drives O2− away from the Ni81Fe19/Pt(O) interface (right). (E) Typical current-voltage (I-V) curves measured across the Ni81Fe19/PtOx/PtOy/Pt junction. The offset of the curves in the vertical direction was shifted for comparison.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/2/eaar2250/DC1

    section S1. Materials’ characterization

    section S2. Second harmonic measurement of the AHE resistance

    section S3. Current-induced magnetization switching

    section S4. Damping modulation

    section S5. Voltage control of spin-orbit torques

    fig. S1. Characterization of Pt(O) films.

    fig. S2. Second harmonic measurement of the AHE resistance.

    fig. S3. Planar Hall effect resistance.

    fig. S4. Pt(O) layer thickness dependence of the second harmonic AHE resistance.

    fig. S5. Current-induced magnetization switching.

    fig. S6. Damping modulation.

    fig. S7. Device fabrication process.

    fig. S8. Voltage control of spin-orbit torques.

  • Supplementary Materials

    This PDF file includes:

    • section S1. Materials’ characterization
    • section S2. Second harmonic measurement of the AHE resistance
    • section S3. Current-induced magnetization switching
    • section S4. Damping modulation
    • section S5. Voltage control of spin-orbit torques
    • fig. S1. Characterization of Pt(O) films.
    • fig. S2. Second harmonic measurement of the AHE resistance.
    • fig. S3. Planar Hall effect resistance.
    • fig. S4. Pt(O) layer thickness dependence of the second harmonic AHE resistance.
    • fig. S5. Current-induced magnetization switching.
    • fig. S6. Damping modulation.
    • fig. S7. Device fabrication process.
    • fig. S8. Voltage control of spin-orbit torques.

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