Research ArticleCONDENSED MATTER PHYSICS

Large Dzyaloshinskii-Moriya interaction induced by chemisorbed oxygen on a ferromagnet surface

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Science Advances  14 Aug 2020:
Vol. 6, no. 33, eaba4924
DOI: 10.1126/sciadv.aba4924
  • Fig. 1 Tuning DMI in the Pd/W(110) system.

    (A, C, and E) Compound SPLEEM images of Ni/Co/Pd/W(110). Scale bar, 2 μm. Gray/black regions represent the down/up magnetization of the perpendicular magnetized domains, respectively, and colored boundaries show the DW magnetization orientation according to the color wheel shown in the inset in (A). White arrows indicate the in-plane magnetization direction in the DW. (B, D, and F) Histograms of angle α between DW magnetization m and DW normal vector n, measured pixel by pixel along the DW centerline, show the evolution of chirality from right-handed Néel-type chirality (B; single peak near 180°), achiral Néel-type chirality (D; two peaks near 0° and 180°), to left-handed Néel-type chirality (F; single peak near 0°). (G) Experimental dPd-dependent Néel-type chirality, which is calculated as (90°90°counts90°270°counts)(90°90°counts+90°270°counts). (H) Calculated effective DMI strength Dij in the 1 ML Ni/3 ML Co/0 to 3 ML Pd/W(110) system.

  • Fig. 2 Chemisorbed oxygen–dependent chirality evolution.

    (A to F) Compound SPLEEM images of O/Ni(1 ML)/Co(3 ML)/Pd(2.76 ML)/W(110); oxygen coverages are labeled for each image. Scale bar, 2 μm. White arrows indicate the in-plane magnetization direction in the DW. (G) Oxygen coverage–dependent histogram of angle α between the DW magnetization m and the DW normal vector n, measured from (A) to (F), showing the evolution of chirality from left-handed Néel type to right-handed Néel type. (H) Oxygen coverage–dependent evolution of Néel-type chirality for different Pd thicknesses.

  • Fig. 3 Quantification of oxygen chemisorption–induced DMI.

    (A) Phase diagram of chirality in dPd-dO space. The dependence of wall texture transition points permits the determination of the oxygen-induced DMI by comparing with Pd thickness–induced DMI variation. (B) Histogram of angle α in the [3Ni/1Co]2/3Ni/2Co/3.46Pd/W(110) multilayer (upper plot, total Ni/Co stack number n = 3) with a single peak near 0°, and histogram of angle α in the [3Ni/1Co]4/3Ni/2Co/3.46Pd/W(110) multilayer (lower plot, n = 5) with double peaks at ~−90° and ~+90°. Modeling the film thickness dependence of this chirality transition allows the determination of the DMI strength of the system. (C and D) Summarized magnitude of the DMI vector at the Ni/[nonmagnetic material] interfaces in (C) and Co/[nonmagnetic material] interfaces in (D), all extracted by the same approach used in this work.

  • Fig. 4 Oxygen-assisted chirality modification at room temperature.

    (A to F) Compound SPLEEM images of a magnetic bubble in perpendicularly magnetized Ni(1 ML)/Co(3 ML)/Pd(2.6 ML)/W(110) with increasing oxygen coverage (labeled in each panel), showing a complete chirality transition from left-handed (A) to achiral (D) to right-handed (F). Scale bars, 1 μm (A and D). The change of the bubble shape is due to the weak oxygen-induced magnetic anisotropy. (G) Compound SPLEEM image of a left-handed Néel-type skyrmion in a perpendicularly magnetized [Co/Ni]3/Cu(111) system. The field of view is 340 nm. Color wheel and white arrows show in-plane magnetization directions. Gray/black regions show out-of-plane components of the magnetization pointing down (−z) or up (+z). (H and I) The Néel-type skyrmion in (G) evolves into a skyrmion with tilted wall and lastly a Bloch-type skyrmion upon oxygen chemisorption [0.12 and 0.21 ML oxygen in (H) and (I), respectively].

Supplementary Materials

  • Supplementary Materials

    Large Dzyaloshinskii-Moriya interaction induced by chemisorbed oxygen on a ferromagnet surface

    Gong Chen, Arantzazu Mascaraque, Hongying Jia, Bernd Zimmermann, MacCallum Robertson, Roberto Lo Conte, Markus Hoffmann, Miguel Angel González Barrio, Haifeng Ding, Roland Wiesendanger, Enrique G. Michel, Stefan Blügel, Andreas K. Schmid, Kai Liu

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