Research ArticleSPINTRONICS

Anomalous spin-orbit torque switching due to field-like torque–assisted domain wall reflection

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Science Advances  21 Apr 2017:
Vol. 3, no. 4, e1603099
DOI: 10.1126/sciadv.1603099
  • Fig. 1 TR-MOKE experimental setup and dc-induced magnetization switching in Ta/CoFeB/MgO.

    (A) Schematic illustration of TR-MOKE measurements. μ0Hx is the external magnetic field. The dc or pulse current is applied along the x axis. The picosecond laser is shined as a probe beam. The patterned perpendicular anisotropy Ta (6 nm)/CoFeB (0.8 nm)/MgO (2 nm) square is connected to a ground (G)–signal (S)–ground (G) coplanar waveguide. (B) dc-induced magnetization switching with various μ0Hx. The data are shifted vertically for clarity. (C) dc switching current density Jc versus μ0Hx.

  • Fig. 2 TR-MOKE measurements of SOT-induced perpendicular magnetization switching in Ta/CoFeB/MgO.

    (A) Temporal evolutions of TR-MOKE signals corresponding to the average z component of magnetization (Mz) in an applied current density (J = 5.2 × 1011 A m−2) of various pulse widths (tpw) from 1 to 5 ns for μ0Hx = −168 mT. The data are shifted vertically for clarity. The current pulse starts at t = 0, and the end of the current pulse is indicated as a red triangle in each curve. The horizontal dashed lines serve as guides to the maximum change in MOKE signal (~7 μV), corresponding to the full magnetization switching from the up to the down state. (B) Time-varying MOKE signal for tpw = 1.8 and 5.0 ns. (C) Switching probability (Psw) as a function of tpw, extracted from Fig. 2A.

  • Fig. 3 Current-dependence of SOT-induced magnetization switching.

    The sample structure is Ta (3 nm)/CoFeB (1.2 nm)/MgO (2 nm)/SiO2 (3 nm). (A) Temporal evolutions of TR-MOKE signals, normalized by the maximum signal change, for various current densities for tpw = 30 ns and μ0Hx = −90 mT. (B) Switching probability (PSW) as a function of tpw at various current densities.

  • Fig. 4 Micromagnetic simulation results for SOT switching at 0 K.

    (A) Temporal evolutions of average Mz/Ms (〈mz〉) at various current pulse widths. (B) Switching parameter (P; 0 = no-switching and 1 = switching) as a function of tpw for J = 15 × 1011 A m−2 and μ0Hx = −200 mT. (C) Temporal evolutions of 〈mz〉 at various current densities for tpw = 1.2 ns and μ0Hx = −200 mT. Snapshots of magnetization configuration (mz = Mz/Ms) at time t for tpw = 1.7 ns (D) and 1.8 ns (E). Yellow arrows show the direction of domain wall motion. (F) Switching parameter P as a function of tpw for various current densities (J = 16 × 1011, 18 × 1011, and 20 × 1011 A m−2).

  • Fig. 5 Domain wall reflection in one-dimensional model.

    (A) Temporal evolutions of the domain wall position q at various FLT to DLT ratios (τfd = c/c||) for c|| = −0.07, J = 6 × 1011 A m−2, and μ0Hx = −200 mT. Δq is the distance for the backward motion of a reflected domain wall. Schematic illustrations of the reflection of a transverse wall at a fixed end (B), and the reflection of a domain wall at an edge (C). (D) Temporal evolutions of domain wall angle φ and domain wall position q for τfd = −2. Domain wall angles φstd, φM, φref, and φ0 are defined in (C) and (D) (see the text for details). (E) φref, φ0, and φstd as a function of τfd. (F) Δq as a function of τfd.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/4/e1603099/DC1

    section S1. Stroboscopic pump-probe MOKE experiments using a picosecond laser

    section S2. Characterization of magnetic films

    section S3. Oscillatory SOT-induced magnetization switching: Micromagnetic simulations

    section S4. Domain wall moving along the left edge

    section S5. Backward motion of a domain wall reflected at an edge

    fig. S1. Stroboscopic pump-probe MOKE setup.

    fig. S2. Vibrating sample magnetometry and MOKE measurements.

    fig. S3. Time-varying z component of the magnetization and its configurations.

    fig. S4. Domain wall types formed in the two-dimensional sample.

    fig. S5. Temporal evolutions of domain wall position q for the Bloch-type domain wall.

    References (4250)

  • Supplementary Materials

    This PDF file includes:

    • section S1. Stroboscopic pump-probe MOKE experiments using a picosecond laser
    • section S2. Characterization of magnetic films
    • section S3. Oscillatory SOT-induced magnetization switching: Micromagnetic simulations
    • section S4. Domain wall moving along the left edge
    • section S5. Backward motion of a domain wall reflected at an edge
    • fig. S1. Stroboscopic pump-probe MOKE setup.
    • fig. S2. Vibrating sample magnetometry and MOKE measurements.
    • fig. S3. Time-varying z component of the magnetization and its configurations.
    • fig. S4. Domain wall types formed in the two-dimensional sample.
    • fig. S5. Temporal evolutions of domain wall position q for the Bloch-type domain wall.
    • References (42–50)

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