Creation of skyrmions in van der Waals ferromagnet Fe3GeTe2 on (Co/Pd)n superlattice

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Science Advances  04 Sep 2020:
Vol. 6, no. 36, eabb5157
DOI: 10.1126/sciadv.abb5157
  • Fig. 1 Crystal structure and element-resolved XMCD measurement.

    (A) Atomic structure of FGT. (B) High-resolution cross-section scanning TEM image (left) and the corresponding electron diffraction patterns of (001)-oriented (top right) and (110)-oriented (bottom right) FGT. There is no evidence of inversion symmetry breaking in the bulk FGT crystal. Element-resolved XMCD measurements from (C) the Co absorption edge and (E) the Fe absorption edge, respectively. a.u., arbitrary units. Both (D) the Co and (F) the Fe hysteresis loops show an out-of-plane easy magnetization axis from Co/Pd multilayers and FGT vdW material. The inset in (D) is the schematic drawing for the hysteresis loop measurement, where θ is the angle between the x-ray incidence direction and the sample surface.

  • Fig. 2 Creating magnetic skyrmions in FGT by the magnetic interlayer coupling between FGT and [Co/Pd]10 multilayers.

    (A) Schematic drawing of the sample structure, where the wedged Pd spacer layer tunes the coupling strength between FGT and perpendicularly magnetized [Co/Pd]10 multilayers. (B) PEEM images of the FGT magnetic domains at three different thicknesses of the Pd spacer layer. The bright and dark contrasts correspond to an out-of-plane magnetization in the +z and –z directions, respectively. The [Co/Pd]10 underlayer was magnetized in the +z direction. Dark stripes are gradually broken into bubbles (skyrmions) as the coupling strength increases by decreasing the Pd thickness. The thicknesses of FGT flakes are 130, 150, and 130 nm, respectively. (C) Magnetic domain images of the FGT obtained at Fe L3 edge (the center flake) and the [Co/Pd]10 obtained at Co L3 edge (surrounding area) at dPd = 0.9 nm after demagnetizing the [Co/Pd]10 into multidomains. The magnetization direction inside the bubbles is always antiparallel to the underlayer [Co/Pd]10 magnetization. (D) FGT normalized magnetization calculated from the areal difference between the bright and the dark domains of the PEEM images and (E) from areal fractions of stripes and bubbles (antiparallel to [Co/Pd]10 magnetization) as a function of Pd spacer layer thickness.

  • Fig. 3 Néel-type skyrmions observed by LTEM in the system of FGT/[Co/Pd]10 multilayers.

    (A) Schematic drawing of sample structure and TEM image of FGT flake on a porous Si3N4 membrane. The thickness of FGT flake here is 70 nm. (B) LTEM images of FGT/[Co/Pd]10 at a sample tilting angle of 30°. (C) LTEM images taken from selected area in (B) (green dashed box) at sample tilting angles of 30°, 0°, and − 30°. The zero contrast at 0° tilting angle and the reversed contrasts at opposite tilting angles indicate the Néel-type structure of the skyrmion. All LTEM measurements were performed at liquid nitrogen temperature. (D) Line profiles of the contrast from the same skyrmion at opposite tilting angles, showing the contrast reversal of the Néel-type skyrmion at opposite tilting angles. (E) The magnetization distribution obtained by exit wave phase reconstruction of the selected LTEM data [black dashed box in (B)]. The white arrows and the color wheel indicate the in-plane direction of the magnetization.

Supplementary Materials

  • Supplementary Materials

    Creation of skyrmions in van der Waals ferromagnet Fe3GeTe2 on (Co/Pd)n superlattice

    M. Yang, Q. Li, R. V. Chopdekar, R. Dhall, J. Turner, J. D. Carlström, C. Ophus, C. Klewe, P. Shafer, A. T. N’Diaye, J. W. Choi, G. Chen, Y. Z. Wu, C. Hwang, F. Wang, Z. Q. Qiu

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