Research ArticleCONDENSED MATTER PHYSICS

Scaling, rotation, and channeling behavior of helical and skyrmion spin textures in thin films of Te-doped Cu2OSeO3

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Science Advances  27 Mar 2020:
Vol. 6, no. 13, eaax2138
DOI: 10.1126/sciadv.aax2138
  • Fig. 1 Real-space observation of magnetic spin textures in Te-doped and undoped CSO thin films.

    (A to C) Sample schematic and Lorentz images of Te-doped and undoped CSO transmission electron microscopy samples at 25 K under residual magnetic field (H ~ 11 mT) along the [1¯10] direction. Four different thickness sections are prepared by focused ion beam for both undoped and doped samples. (D to G) Magnetic induction maps reconstructed by the phase retrieval method for doped (D) and (F) and undoped (E) and (G) samples, respectively, showing helical spin states (D) and (E) and hexagonally packed SkLs (F) and (G). Color wheel shown in the center represents amplitude and direction of magnetization.

  • Fig. 2 Evolution of spin textures under various magnetic field.

    Helical-to-skyrmion phase transition in Te-doped CSO observed by Lorentz microscopy at 25 K under various external magnetic fields (H) along the [110] direction (A to E). Lorentz phase images from three different thicknesses (69, 100, and 141 nm, respectively) and their corresponding diffractograms (right) showing field and thickness dependence of the spin textures. Anisotropic scaling of two orthogonal helical phases, edge-induced skyrmion nucleation, and skyrmion channeling are observed upon magnetic field application.

  • Fig. 3 Thickness controlled skyrmion “channeling.”

    Skyrmions nucleated at edges in the thinnest section gradually channel across thicker sections. Both doped (A to C) and undoped (D to F) samples show skyrmion channeling. Red dashed lines separate SkL1 and SkL2.

  • Fig. 4 Anisotropic scaling behavior of helical spin states.

    (A) Anisotropic contribution to the energy of the spin spiral in domains I and II at H/(ρQ2) = 0.5, β/(ρQ2) = 0.1, keff/(ρQ2) = 0.5. (B and C) Comparison of experimental data on the scaling of the measured spin spiral wave vector Q|| versus perpendicular magnetic field H in (A) undoped CSO, (C) Te-doped CSO. Squares show experimental data, and blue, red, and cyan solid lines are the fit with the theoretical formula, eq. S7. The open (filled) markers correspond to spirals in domain I, the h[001] phase (domain II, the h[110] phases). The black solid line is the theoretical prediction for the domain I, λ = λ0. (D) Extracted value of the phenomenological parameter β versus sample thickness t. The solid lines show β (t) ∝ 1/t.

  • Fig. 5 Tilting of the helical propagation vector in finite field.

    Left: Out-of-plane tilting of the spin h[110] spiral in the external magnetic field (domain II) H||z. Right: Orientation of the crystal axes in the CSO sample.

  • Fig. 6 Phase diagrams as function of doping and thickness.

    Magnetic field–temperature phase maps of the both doped (A to D) and undoped (E to H) CSO crystals with increasing film thickness, respectively. The doped sample shows the SkL stability is more strongly dependent on film thickness compared to the undoped sample. Both doped and undoped samples show that SkLs are more stable with decreasing film thickness.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/13/eaax2138/DC1

    X-ray diffraction

    Energy-dispersive x-ray spectroscopy

    Second skyrmion phase at lower T and higher magnetic field

    Micromagnetic simulation

    Theoretical analysis

    Table S1. Crystal data and structure refinement for Cu2OSe(Te)O3.

    Table S2. Fractional atomic coordinates and equivalent isotropic displacement parameters (Å2 × 103).

    Table 3. Anisotropic displacement parameters (Å2 × 103).

    Fig. S1. Energy-dispersive x-ray spectroscopy maps of Cu, Se, O, and Te.

    Fig. S2. Skyrmion phase diagrams obtained from Te-doped and undoped TEM samples with relatively uniform thickness (~150 nm).

    Fig. S3. Micromagnetic simulations.

    Movie S1. Video of Te-doped sample under increasing magnetic field at 15 K.

    Movie S2. Video of Te-doped sample under increasing magnetic field at 25 K.

    Movie S3. Video of Te-doped sample under increasing magnetic field at 40 K.

    Movie S4. Video of undoped sample under increasing magnetic field at 15 K.

    Movie S5. Video of undoped sample under increasing magnetic field at 25 K.

    Movie S6. Video of undoped sample under increasing magnetic field at 40 K.

    References (53, 54)

  • Supplementary Materials

    The PDF file includes:

    • X-ray diffraction
    • Energy-dispersive x-ray spectroscopy
    • Second skyrmion phase at lower T and higher magnetic field
    • Micromagnetic simulation
    • Theoretical analysis
    • Table S1. Crystal data and structure refinement for Cu2OSe(Te)O3.
    • Table S2. Fractional atomic coordinates and equivalent isotropic displacement parameters (Å2 × 103).
    • Table 3. Anisotropic displacement parameters (Å2 × 103).
    • Fig. S1. Energy-dispersive x-ray spectroscopy maps of Cu, Se, O, and Te.
    • Fig. S2. Skyrmion phase diagrams obtained from Te-doped and undoped TEM samples with relatively uniform thickness (~150 nm).
    • Fig. S3. Micromagnetic simulations.
    • Legends for movies S1 to S6
    • References (53, 54)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.avi format). Video of Te-doped sample under increasing magnetic field at 15 K.
    • Movie S2 (.avi format). Video of Te-doped sample under increasing magnetic field at 25 K.
    • Movie S3 (.avi format). Video of Te-doped sample under increasing magnetic field at 40 K.
    • Movie S4 (.avi format). Video of undoped sample under increasing magnetic field at 15 K.
    • Movie S5 (.avi format). Video of undoped sample under increasing magnetic field at 25 K.
    • Movie S6 (.avi format). Video of undoped sample under increasing magnetic field at 40 K.

    Files in this Data Supplement:

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