Structure-property relationship of reversible magnetic chirality tuning

Letter

Structure-property relationship of reversible magnetic chirality tuning

Jing Qi, Paula M. Weber, Tilman Kißlinger, Lutz Hammer, M. Alexander Schneider, and Matthias Bode

Phys. Rev. B 107, L060409 – Published 22 February 2023

Abstract

The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction mediates collinear magnetic interactions via the conduction electrons of a nonmagnetic spacer, resulting in a ferro- or antiferromagnetic magnetization in magnetic multilayers. Recently it has been discovered that heavy nonmagnetic spacers are able to mediate an indirect magnetic coupling that is noncollinear and chiral. This Dzyaloshinskii-Moriya-enhanced RKKY interaction causes the emergence of a variety of interesting magnetic structures, such as skyrmions and spin spirals. Here, we show by spin-polarized scanning tunneling microscopy that the interchain coupling between manganese oxide chains on Ir(001) can reproducibly be switched from chiral to collinear antiferromagnetic by increasing the oxidation state of ${MnO}_{2}$ , while the reverse process can be induced by thermal reduction. The underlying structure–property relationship is revealed by low-energy electron diffraction intensity analysis. Density functional theory calculations suggest that the magnetic transition may be caused by a significant increase of the Heisenberg exchange which overrides the Dzyaloshinskii-Moriya interaction upon oxidation.

Received 16 August 2022
Revised 21 November 2022
Accepted 9 February 2023

DOI:https://doi.org/10.1103/PhysRevB.107.L060409

Physics Subject Headings (PhySH)

Composition Magnetism RKKY interaction Structural properties

1-dimensional spin chains Chiral magnets Crystalline systems Magnetic systems

Density functional theory Low-energy electron diffraction Spin-polarized scanning tunneling microscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Jing Qi ¹, Paula M. Weber ¹, Tilman Kißlinger², Lutz Hammer ², M. Alexander Schneider ^2,*, and Matthias Bode ^1,3,†

¹Physikalisches Institut, Experimentelle Physik II, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany
²Solid State Physics, Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstrasse 7, 91058 Erlangen, Germany
³Wilhelm Conrad Röntgen-Center for Complex Material Systems (RCCM), Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany

^*Corresponding author: alexander.schneider@fau.de
^†Corresponding author: bode@physik.uni-wuerzburg.de

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Issue

Vol. 107, Iss. 6 — 1 February 2023

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Images

Figure 1
(a) Scheme of the sample preparation procedures. Depending on the oxygen pressure $p_{O_{2}}$ during the final annealing step, different ${MnO}_{x}$ stoichiometries with $x = 2$ or $x > 2$ are obtained. (b) Large-scale STM topographic image of a sample prepared at low $p_{O_{2}}$ . ${MnO}_{2}$ chains are oriented along the [110] and $[1 \bar{1} 0]$ direction of Ir(001) (scan parameters: $U = 100 mV$ , $I = 500 pA$ ). (c),(d) Atomic resolution images scanned with a nonmagnetic tungsten tip and a magnetic Mn tip ( $U = 100 mV$ , $I = 1 nA$ ). (e) Line profiles measured on the chains indicated by colored markers in (c) and (d) showing a doubling of the $a_{Ir}$ period in (d) as well as a systematic variation of amplitudes and phases between green, blue, and red line profiles, characteristic for chiral magnetic order across ${MnO}_{2}$ chains. (f) Model of the ( $9 \times 2$ ) ${MnO}_{2}$ structure. Gray, red, and yellow spheres represent Ir, O, and Mn atoms, respectively. Mn spin orientation is marked by black arrows. (g) Large scale STM image of a similar surface as in (a), but prepared at high $p_{O_{2}}$ ( $U = 100 mV$ , $I = 50 pA$ ). (h),(i) Atomic resolution STM images of the $c (6 \times 2)$ ${MnO}_{x}$ chain structure scanned with a nonmagnetic and a Mn-coated magnetic tip, respectively [(h) $U = 50 mV$ , $I = 1 nA$ ; (i) $U = 300 mV$ , $I = 0.5 nA$ ]. (j) Line profiles along the lines in (h) and (i), showing a doubling of the periodicity in (i) compared to that of (h) and an antiphase relation between neighboring rows. (k) Model of the $c (6 \times 2)$ ${MnO}_{x}$ structure.
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Figure 2
LEED patterns of $1 / 3 ML$ Mn oxidized in (a) $p_{O_{2}} = 5 \times 10^{- 8} mbar$ molecular $O_{2}$ and (b) in $p_{{NO}_{2}} = 1 \times 10^{- 6} mbar$ (for exact conditions see text). The intensity spectrum of the spot marked in (b) is shown in Fig. 3. (c) Top and side view of the $(3 \times 1) {MnO}_{3} + O_{br}$ structure and relevant structural parameters as obtained by LEED-IV structural analysis of the preparation in (b). The resulting parameters of the DFT energy minimization are given in brackets.
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Figure 3
Intensity spectra of the $k_{| |} = (2 / 3 1)$ beam. (a) Comparison of the normalized intensity between the experimental (red) and the calculated (blue) spectrum of the ${MnO}_{3} + O_{br}$ structure (single beam $R$ factor $R = 0.091$ ). (b) Comparison between experimental spectra obtained from the $(3 \times 1) {MnO}_{2}$ at 13 ML Mn (lowest curve, blue) of the $(3 \times 1) {MnO}_{3} + O_{br}$ prepared by oxidation in ${NO}_{2}$ (top curve, red), and a preparation comparable to that when the $c (6 \times 2)$ magnetic supercell occurs (middle curve, green). The middle curve is scaled by a factor of 2. The visual agreement between the middle and upper curve is substantiated by an $R$ factor of $R = 0.14$ . Curves in (b) are offset for clarity.
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