Sensing Noncollinear Magnetism at the Atomic Scale Combining Magnetic Exchange and Spin-Polarized Imaging

Storing and accessing information in atomic-scale magnets requires magnetic imaging techniques with single-atom resolution. Here, we show simultaneous detection of the spin-polarization and exchange force, with or without the flow of current, with a new method, which combines scanning tunneling microscopy and non-contact atomic force microscopy. To demonstrate the application of this new method, we characterize the prototypical nano-skyrmion lattice formed on a monolayer of Fe/Ir(111). We resolve the square magnetic lattice by employing magnetic exchange force microscopy, demonstrating its applicability to non-collinear magnetic structures, for the first time. Utilizing distance-dependent force and current spectroscopy, we quantify the exchange forces in comparison to the spin-polarization. For strongly spin-polarized tips, we distinguish different signs of the exchange force which we suggest arises from a change in exchange mechanisms between the probe and a skyrmion. This new approach may enable both non-perturbative readout combined with writing by current-driven reversal of atomic-scale magnets

Probing Single Vacancies in Black Phosphorus at the Atomic Level

Utilizing a combination of low-temperature scanning tunneling microscopy/spectroscopy (STM/STS) and electronic structure calculations, we characterize the structural and electronic properties of single atomic vacancies within several monolayers of the surface of black phosphorus. We illustrate, with experimental analysis and tight-binding calculations, that we can depth profile these vacancies and assign them to specific sublattices within the unit cell. Measurements reveal that the single vacancies exhibit strongly anisotropic and highly delocalized charge density, laterally extended up to 20 atomic unit cells. The vacancies are then studied with STS, which reveals in-gap resonance states near the valence band edge and a strong p-doping of the bulk black phosphorus crystal. Finally, quasiparticle interference generated near these vacancies enables the direct visualization of the anisotropic band structure of black phosphorus.Comment: Nano Letters (2017

Revealing the correlation between real-space structure and chiral magnetic order at the atomic scale

We image simultaneously the geometric, electronic and magnetic structure of a buckled iron bilayer film that exhibits chiral magnetic order. We achieve this by combining spin-polarized scanning tunneling microscopy and magnetic exchange force microscopy (SPEX), to independently characterize the geometric as well as the electronic and magnetic structure of non-flat surfaces. This new SPEX imaging technique reveals the geometric height corrugation of the reconstruction lines resulting from strong strain relaxation in the bilayer, enabling the decomposition of the real-space from the eletronic structure at the atomic level, and the correlation with the resultant spin spiral ground state. By additionally utilizing adatom manipulation, we reveal the chiral magnetic ground state of portions of the unit cell that were not previously imaged with SP-STM alone. Using density functional theory (DFT), we investigate the structural and electronic properties of the reconstructed bilayer and identify the favorable stoichiometry regime in agreement with our experimental result

AFM Imaging of Mercaptobenzoic Acid on Au(110) : Submolecular Contrast with Metal Tips

A self-assembled monolayer of mercaptobenzoic acid (MBA) on Au(110) is investigated with scanning tunneling and atomic force microscopy (STM and AFM) and density functional calculations. High-resolution AFM images obtained with metallic tips show clear contrasts between oxygen atoms and phenyl moieties. The contrast above the oxygen atoms is due to attractive covalent interactions, which is different than previously reported high-resolution images, where Pauli repulsion dominated the image contrast. We show that the bonding of MBA to the substrate occurs mainly through dispersion interactions, whereas the thiol-Au bond contributes only a quarter of the adsorption energy. No indication of Au adatoms mediating the thiol-Au interaction was found in contrast to other thiol-bonded systems. However, MBA lifts the Au(110)-(2 × 1) reconstruction

Quantifying Exchange Forces of a Non-Collinear Magnetic Structure on the Atomic Scale

The large interest in chiral magnetic structures for realization of nanoscale magnetic storage or logic devices has necessitated methods which can quantify magnetic interactions at the atomic scale. To overcome the limitations of the typically used current-based sensing of atomic-scale exchange interactions, a force-based detection scheme is highly advantageous. Here, we quantify the atomic-scale exchange force field between a ferromagnetic tip and a cycloidal spin spiral using our developed combination of current and exchange force detection. Compared to the surprisingly weak spin polarization, the exchange force field is more sensitive to atomic-scale variations in the magnetization. First-principles calculations reveal that the measured atomic-scale variations in the exchange force originate from different contributions of direct and indirect (Zener) type exchange mechanisms, depending on the chemical tip termination. Our work opens the perspective of quantifying different exchange mechanisms of chiral magnetic structures with atomic-scale precision using 3D magnetic exchange force field measurements

Die Fresken des Tiroler Rokokomalers Christoph Anton Mayr

Die vorliegende Masterarbeit beschäftigt sich mit dem sakralen Freskenwerk des Tiroler Rokokomalers Christoph Anton Mayr. Der Fokus liegt dabei auf den von ihm verwendeten Gestaltungsmitteln, die einerseits genauer untersucht und andererseits deren Rezeptionsgeschichte dargelegt wird. Der um 1720 in Schwaz geborene Künstler hat nicht weniger als 27 Kirchen- und Kapellenausstattungen in Tirol, Salzburg und Südtirol vorzuweisen, wobei fünf Frühwerke und vier Hauptwerke einer näheren Betrachtung unterzogen werden. Dieser Untersuchung geht ein Überblick der barocken Deckenmalerei ab dem späten 17. Jahrhundert in Österreich und Süddeutschland voran. Hierbei werden die, zum einen für die generelle Entwicklung und zum anderen für Mayr, relevantesten Maler herangezogen und einige Werkbeispiele analysiert. Dieser einführende Überblick fungiert sowohl als Basis für die Untersuchung Mayrs Fresken als auch für sämtliche malerische Prinzipien, die für die Künstler des 18. Jahrhunderts von Bedeutung waren. Um die Person des Malers näher vorzustellen, werden sein künstlerischer Werdegang nachskizziert und sämtliche (heute bekannte) freskalen Arbeiten aufgelistet. Im Hauptkapitel werden die bedeutendsten Kirchenausstattungen Mayrs herangezogen und auf signifikante Merkmale in der Komposition untersucht, diese benannt und klassifiziert. Als unabdingbare Methodik zeichnet sich dabei der Vergleich mit Vorgängern aus. Die Rezeptionsgeschichte der verwendeten Gestaltungsprinzipien verweist auf einen starken süddeutschen Einfluss, den Mayr in seinen Fresken verarbeitet hat. Das Ziel der Arbeit ist die kunsthistorische Einordnung des Tiroler Malers, welche auf seine Kenntnisse und Fähigkeiten im Bereich der barocken Deckenmalerei zurückzuführen ist

Switching and charging of a ruthenium dye on Ag(111)

International audienc

Submolecular resolution in scanning probe images of Sn-phthalocyanines on Cu(1 0 0) using metal tips

| openaire: EC/FP7/610446/EU//PAMSSingle Sn-phthalocyanine (SnPc) molecules adsorb on Cu(1 0 0) with the Sn ion above (Sn-up) or below (Sn-down) the molecular plane. Here we use a combination of atomic force microscopy (AFM), scanning tunnelling microscopy (STM) and first principles calculations to understand the adsorption configuration and origin of observed contrast of molecules in the Sn-down state. AFM with metallic tips images the pyrrole nitrogen atoms in these molecules as attractive features while STM reveals a chirality of the electronic structure of the molecules close to the Fermi level EF, which is not observed in AFM. Using density functional theory calculations, the origin of the submolecular contrast is analysed and, while the electrostatic forces turn out to be negligible, the van der Waals interaction between the phenyl rings of SnPc and the substrate deform the molecule, push the pyrrole nitrogen atoms away from the substrate and thus induce the observed submolecular contrast. Simulated STM images reproduce the chirality ofthe electronic structure near EF.Peer reviewe