Atomic-scale spin-engineering and dynamics of novel nano-magnets
Final Report Abstract
The Emmy Noether group was established in Hamburg in August of 2013. After one year, I relocated to Radboud University, Nijmegen, where I accepted a department head and full professorship, to rebuild the Scanning Probe Microscopy department. The project moved but the PhD student and postdoc originally funded stayed in Hamburg. While establishing the new group in Nijmegen, many of the Emmy Noether projects continued in collaboration with the Hamburg colleagues, while we restarted the activity to construct the new mK instrumentation along with a new laboratory. The mK system was completed and fully benchmarked in 2018. Construction of the mK system was delayed on many fronts, due to relocation. In addition to establishing a new department, funding for new members had to be raised, as well as a new laboratory constructed. To this end, the project was also granted a renewal. Nevertheless, the project was extremely successful. Aside from the scientific achievement in establishing a new cutting-edge facility, we successfully explored the magnetic properties of atomic-scale magnets, both derived from 3d magnetic impurities and 4f magnetic impurities on many new surfaces. The highlight of the project was the investigation of the magnetic properties of single Fe atoms on Pt(111), and the subsequent coupling between Fe atoms. We discovered strong non-collinear and indirect exchange between these atoms, and quantified this in terms of a distance-dependent DMI. We also utilized this information to build spin spiral structures, atom-by-atom, as well as stable non-collinear magnets which exhibit bi-stability in the magnetization reversal. Tangentially, we developed two new states of the art in magnetic imaging. As originally proposed, we have developed a sub-Kelvin, specifically a new state of the art in mK-STM capable of spin-resolved imaging, atomic manipulation, and high frequency measurements. This instrument is now online, and the details of the instrumentation were published in 2018. We are currently testing the high frequency aspects of this instrument, as a final step of the original objective, and continuing new single atom magnetism projects. Secondly, we developed a new methodology to characterize atomic and surface magnetic structures, combining SP-STM and MExFM, or so-called SPEX imaging. This unplanned development resulted from the available instrumentation, after relocation to Nijmegen. The added capability of this rather unique method enabled us to combine these imaging methods, as well as their spectroscopic methods (e.g. I-z, F-z). It also will allow us to disentangle current-based detection from the dynamics of atomic scale magnets, an important ingredient to understanding the atomic-scale magnetization dynamics. We demonstrated the capability of this method with chiral magnetic ground states of Fe films on Ir(111). We published 23 papers within this project, and numerous talks were given at international conferences including a number of invited talks as well as invited institute visits. The project has also enabled numerous new and exciting funding opportunities, including a VIDI award in 2015, and after the project ending, a new ERC Consolidator Grant. The established new mK system is one of the world’s highest resolution microscope, capable of spin-resolved imaging and atomic manipulation, and opens up numerous exciting scientific opportunities to pursue magnetization dynamics studies of single atoms.
Publications
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Spin Excitations of Individual Fe Atoms on Pt(111): Impact of the Site-Dependent Giant Substrate Polarization, Physical Review Letters 111, 157204 (2013)
A. A. Khajetoorians, T. Schlenk, B. Schweflinghaus, M. dos Santos Dias, M. Steinbrecher, M. Bouhassoune, S. Lounis, J. Wiebe and R. Wiesendanger
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Tuning emergent magnetism in a Hund's impurity, Nature Nanotechnology 10, 958-964 (2015)
A. A. Khajetoorians, M. Valentyuk, M. Steinbrecher, T. Schlenk, A. Shick, J. Kolorenc, A. I. Lichtenstein, T. O. Wehling, R. Wiesendanger and J. Wiebe
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Absence of a spin-signature from a single Ho adatom as probed by spin-sensitive tunneling, Nature Communications 7, 10454 (2016)
M. Steinbrecher, A. Sonntag, M. d. S. Dias, M. Bouhassoune, S. Lounis, J. Wiebe, R. Wiesendanger and A. A. Khajetoorians
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Tailoring the chiral magnetic interaction between two individual atoms, Nature Communications 7, 10620 (2016)
A. A. Khajetoorians, M. Steinbrecher, M. Ternes, M. Bouhassoune, M. d. S. Dias, S. Lounis, J. Wiebe and R. Wiesendanger
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A gateway towards non-collinear spin processing using three-atom magnets with strong substrate coupling, Nature Communications 8 (1), 642 (2017)
J. Hermenau, J. Ibañez-Azpiroz, C. Hübner, A. Sonntag, B. Baxevanis, K. T. Ton, M. Steinbrecher, A. A. Khajetoorians, M. dos Santos Dias, S. Blügel, R. Wiesendanger, S. Lounis and J. Wiebe
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Sensing Noncollinear Magnetism at the Atomic Scale Combining Magnetic Exchange and Spin-Polarized Imaging, Nano Letters 17 (9), 5660-5665 (2017)
N. Hauptmann, J. W. Gerritsen, D. Wegner and A. A. Khajetoorians
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Spin-Resolved Spectroscopy of the Yu-Shiba-Rusinov States of Individual Atoms, Physical Review Letters 119 (19), 197002 (2017)
L. Cornils, A. Kamlapure, L. Zhou, S. Pradhan, A. A. Khajetoorians, J. Fransson, J. Wiebe and R. Wiesendanger
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An orbitally derived single-atom magnetic memory, Nature Communications 9 (1), 3904 (2018)
B. Kiraly, A. N. Rudenko, W. M. J. van Weerdenburg, D. Wegner, M. I. Katsnelson and A. A. Khajetoorians
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Design and performance of an ultra-high vacuum spin-polarized scanning tunneling microscope operating at 30 mK and in a vector magnetic field, Review of Scientific Instruments 89 (3), 033902 (2018)
H. von Allwörden, A. Eich, E. J. Knol, J. Hermenau, A. Sonntag, J. W. Gerritsen, D. Wegner and A. A. Khajetoorians
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Non-collinear spin states in bottom-up fabricated atomic chains, Nature Communications 9 (1), 2853 (2018)
M. Steinbrecher, R. Rausch, K. T. That, J. Hermenau, A. A. Khajetoorians, M. Potthoff, R. Wiesendanger and J. Wiebe
