Research ArticleAPPLIED PHYSICS

Full voltage manipulation of the resistance of a magnetic tunnel junction

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Science Advances  13 Dec 2019:
Vol. 5, no. 12, eaay5141
DOI: 10.1126/sciadv.aay5141
  • Fig. 1 Voltage manipulation of the MTJ by one pair of electrodes.

    (A) Schematic of the experimental setup. One pair of AA electrodes was deposited on the PMN-PT, and an elliptical MTJ device of 18 × 6 μm2 was placed at the center of the gap. Voltage was applied to the AA electrodes to generate localized strain, and the bottom of the substrate was grounded. (B) The detailed structure of the MgO-based MTJ device. To enhance the performance of the devices, we used both the antiferromagnetic layer IrMn and the artificial antiferromagnetic structure of CoFe/Ru/CoFeB. With this particular design, at zero magnetic field, the top CoFeB layer acts as a free layer whose magnetization can be tuned by voltage, whereas the magnetization of the bottom CoFeB layer is fixed because of the pinning effect of the antiferromagnetic IrMn layer. (C) Simulated anisotropic strain distribution upon applying 400 V to the AA electrodes using finite element analysis. A uniform localized tensile strain along the y direction was generated at the central gap of the electrode pair. The dashed-line boxes illustrate the locations of the electrodes. (D) MR curves with 0 and 400 V applied at the AA electrodes. (E) Dependence of resistance on voltage applied to the AA electrodes under H = 0 Oe. The dashed lines denote the various magnetization configurations of the MTJ, as illustrated by the insets, i.e., antiparallel (red), perpendicular (purple), and parallel (blue). a.u., arbitrary units.

  • Fig. 2 Tuning the magnetic anisotropy of the free layer by voltage using two pairs of electrodes.

    (A) Schematic top view of the sample structure with two pairs of AA and BB electrodes. An elliptical MTJ device of 18 × 6 μm2 was placed at the center of two electrode pairs. The major axis of the elliptical device was along the x axis. The pinning direction of the MTJ was along the [100] direction of the PMN-PT substrate (+x axis). The joint line of the AA electrodes was perpendicular to the pinning direction, while that of the BB electrodes deviated from the pinning direction by 45°. (B to E) Polar curves of the angular-dependent MR/MS of a CoFeB layer, when the applied voltages were 0 V (B), BB 200 V (C), AA 400 V (D), and BB −200 V (E). The [100] direction of the PMN-PT substrate was defined as 0°. The double-headed arrows indicate the direction of the magnetic easy axis.

  • Fig. 3 Reversible and nonvolatile full control of MTJs by voltage-driven 180° magnetization switching.

    (A to H) Simulated magnetization profiles of the free layer at various voltages applied to the AA and BB electrode pairs. A 180° magnetization switching was accomplished by implementing sequential voltages of 0 V (A) → BB 200 V (B) → AA 400 V (C) → BB −200 V (D) → 0 V (E) via successive unidirectional 45° rotations, and the M reverted back to the initial state after the same sequential voltages were implemented (E to H), suggesting reversibility and nonvolatility. The arrows schematically indicate the magnetization directions of the free layer. (I) Dependence of the resistance of an MTJ on voltage synergistically applied to the AA and BB electrode pairs at H = 0 Oe. The reversible resistance switching between high- and low-resistance states corresponds to the antiparallel and parallel magnetization configurations of the MTJ, as illustrated by the insets, which indicates the 180° magnetization switching of the free layer driven by voltage. The red, purple, and blue dashed lines denote the antiparallel, perpendicular, and parallel magnetization configurations of the MTJ, respectively. The stable resistance states with a giant modulation of approximately 200%, highlighted by the vertical pink and blue shaded lines, demonstrate that this 180° magnetization switching and full control of MTJs by voltage are reversible and nonvolatile.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/12/eaay5141/DC1

    Fig. S1. The localized strain induced by a voltage of 400 V applied on shorted AA electrodes.

    Fig. S2. Modulating the magnetic property of the CoFeB layer by voltage-induced localized strain using electrode pair AA.

    Fig. S3. The voltage-induced localized strain by activating the BB electrodes.

    Fig. S4. Optical image of an MTJ cell with two pairs of AA and BB electrodes.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. The localized strain induced by a voltage of 400 V applied on shorted AA electrodes.
    • Fig. S2. Modulating the magnetic property of the CoFeB layer by voltage-induced localized strain using electrode pair AA.
    • Fig. S3. The voltage-induced localized strain by activating the BB electrodes.
    • Fig. S4. Optical image of an MTJ cell with two pairs of AA and BB electrodes.

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