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Atomic-scale magnetic moments in contact with superconductors host rich physics based on the emergence of Yu–Shiba–Rusinov (YSR) magnetic bound states within the superconducting condensate. Here, we focus on a magnetic bound state induced into Pb nanoislands by individual vanadyl phthalocyanine (VOPc) molecules deposited on the Pb surface. The VOPc molecule is characterized by a spin magnitude of 1/2 arising from a well-isolated singly occupied dxy-orbital and is a promising candidate for a molecular spin qubit with long coherence times. X-ray magnetic circular dichroism (XMCD) measurements show that the molecular spin remains unperturbed even for molecules directly deposited on the Pb surface. Scanning tunneling spectroscopy and density functional theory (DFT) calculations identify two adsorption geometries for this “asymmetric” molecule (i.e., absence of a horizontal symmetry plane): (a) oxygen pointing toward the vacuum with the Pc laying on the Pb, showing negligible spin–superconductor interaction, and (b) oxygen pointing toward the Pb, presenting an efficient interaction with the Pb and promoting a Yu–Shiba–Rusinov bound state. Additionally, we find that in the first case a YSR state can be induced smoothly by exerting mechanical force on the molecules with the scanning tunneling microscope (STM) tip. This allows the interaction strength to be tuned continuously from an isolated molecular spin case, through the quantum critical point (where the bound state energy is zero) and beyond. DFT indicates that a gradual bending of the VO bond relative to the Pc ligand plane promoted by the STM tip can modify the interaction in a continuously tunable manner. The ability to induce a tunable YSR state in the superconductor suggests the possibility of introducing coupled spins on superconductors with switchable interaction.

Spin waves with wavelengths in the nanometre range could serve as data carriers in future magnonic logic or signal processing devices. We investigate the interference of spin waves emitted from magnetic vortices in two exchange-coupled vortex stacks. The spin-wave dynamics are studied using scanning transmission X-ray microscopy and micromagnetic simulations. Stacks of vortices provide an excellent controllability of spin-wave properties including a tunable wavelength in the 100 nm regime and manipulation of their propagation direction via the magnetisation configuration. Furthermore, interference gives rise to amplified or reduced spin-wave amplitudes in distinct areas of the structure providing controlled confinement crucial for future applications of spin waves. Spin waves are promising candidates as a building block for future magnonic devices. The authors present a combined numerical and experimental study of spin-wave interferences in stacks of magnetic vortices that are efficient spin-wave emitters in the nanometre regime.

A novel approach to investigate geometrical frustration is introduced using two-dimensional magnonic vortex crystals. The frustration of the crystal can be manipulated and turned on and off dynamically on the timescale of milliseconds. The vortices are studied using scanning transmission x-ray microscopy and ferromagnetic resonance spectroscopy. They are arranged analogous to the nanomagnets in artificial spin-ice systems. The polarization state of the vortices is tuned in a way that geometrical frustration arises. We demonstrate that frustrated polarization states and non-frustrated states can be tuned to the crystal by changing the frequency of the state formation process.

Spin injection from epitaxial iron into InGaAs/InAs quantum wells is observed using an all-electric nonlocal setup. From the choice of material, a significant spin-orbit interaction (SOI) is expected. The contact separation of the spin-valve devices is in the order of the mean free path so that the transport is at the transition between diffusive and ballistic. With an established purely diffusive model a spin-injection efficiency of $77%$ is determined from the data. This value is very large compared to previous observations on diffusive spin-valve devices on similar material systems. Motivated by similar results on ballistic spin-valve devices in a material system with small spin-orbit coupling, a recent model was suggested in which a ballistic spin-dephasing length was pointed out to be the crucial length scale. With this model and an experimentally determined spin-orbit coupling parameter of $\ensuremath{\alpha}=4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ eV m, very high spin-injection efficiencies are still determined in our quantum wells. We suggest that the spin-dephasing length to be used in the model must be larger due to the crystallographic anisotropy of the spin-orbit coupling, i.e., in our setup the SOI stabilizes the spin in the crystal direction of the spin-polarized current.

Collective modes in three-dimensional crystals of stacked permalloy disks with magnetic vortices are investigated by ferromagnetic resonance spectroscopy and scanning transmission X-ray microscopy. The size of the arrangements is increased step by step to identify the different contributions to the interaction between the vortices. These contributions are the key requirement to understand complex dynamics of three dimensional vortex crystals. Both vertical and horizontal coupling determine the collective modes. In-plane dipoles strongly influence the interaction between the disks in the stacks and lead to polarity-dependent resonance frequencies. Weaker contributions discern arrangements with different polarities and circularities that result from the lateral coupling of the stacks and the interaction of the core regions inside a stack. All three contributions are identified in the experiments and are explained in a rigid particle model.

With scanning transmission x-ray microscopy we study six magnetostatically coupled vortices arranged in a ring that resembles a benzene molecule. Each vortex is contained in a ferromagnetic microdisk. When exciting one vortex of the ring molecule with an alternating magnetic high-frequency field, all six vortices perform gyrations around the equilibrium center positions in their disks. In a rigid particle model, we derive the dispersion relation for these modes. In contrast to carbon atoms, magnetic vortices have a core polarization that strongly influences the intervortex coupling. We make use of this state parameter to reprogram the dispersion relation of the vortex molecule experimentally by tuning a homogeneous and an alternating polarization pattern. In analogy to the benzene molecule, we observe motions that can be understood in terms of normal modes that are largely determined by the symmetry of the system.

Magnonic vortex crystals are studied via scanning transmission x-ray microscopy and ferromagnetic-resonance spectroscopy. We investigate a two-dimensional vortex crystal by imprinting waves with tunable wave vectors. The dispersion relation $\ensuremath{\omega}(k)$ is determined via ferromagnetic-resonance spectroscopy with a tunable frequency and wave vector for two vortex core polarization patterns that are adjusted by self-organized state formation prior to the measurement. We demonstrate that the band structure of the crystal is reprogrammed by tuning the vortex polarizations.

The manipulation of polarization states in $4\ifmmode\times\else\texttimes\fi{}4$ vortex crystals using sinusoidal magnetic field bursts is investigated by means of a broadband ferromagnetic-resonance setup. Magnetic field excitation with the proper amplitude and frequency allows tuning different polarization states, which are observed in the measured absorption spectra. The variation of the sinusoidal burst width consecutively identifies the time scale of the underlying process. A memorylike polarization state writing process is demonstrated on the submicrosecond time scale.

The gyrotropic eigenmodes in magnetic vortex crystals are studied by means of broadband ferromagnetic-resonance measurements. An artificial crystal structure is realized with two staggered ellipses as building block. Making use of the anisotropic field dependence of the vortex resonance frequency in a ferromagnetic ellipse, distinct resonance modes can be observed that are easily tunable via a small magnetic bias field. The gap between the modes can be continuously adjusted. In the presence of dipolar interaction, a bending and shifting of the modes is observed. A rigid particle model is adopted to analytically describe the experimental results. Calculations for the crystal basis reveal an anticrossing of the resonance modes depending on the vortex-core polarization configuration.

Complexity created by periodic arrangement of well-understood building blocks plays an important role in biochemistry, photonics, engineering and nanoelectrics. The periodic arrangement of atoms or molecules as basis determines the physical properties of crystals. With the flexibility of nanometer precise electron-beam lithography here magnetic interactions are engineered yielding two-dimensional magnonic crystals that benefit from the magnetic vortex core as crystal basis. Using scanning transmission X-ray microscopy at the MAXYMUS beamline at BESSY II in Berlin, Germany the magnonic crystal dynamics are imaged with time resolution in the sub-nanosecond regime and simultaneous spatial resolution on the nanometer scale. Self-organized vortex core state formation by adiabatic reduction of a high frequency magnetic field excitation is observed. The emerging polarization states are shown to depend on the frequency of excitation and the strength of the dipolar interaction between the elements. In spite of the complexity of the investigated system, global order caused by local interactions creates polarization states with a high degree of symmetry. An analytical dipole model and numerically solved coupled equations of motion are adopted to analytically describe the experimental results. The emerging states can be predicted by a fundamental stability criterion based on the excitability of eigenmodes in the crystal. Further experiments with ferromagnetic absorption spectroscopy are carried out that give insight into the characteristic frequencies of the vortex dynamics that are crucially influenced by the self-organized state formation. This is emphasized with experiments on benzene-like magnetic vortex molecules whose motions show strong similarities to the vibrational modes of the actual benzene molecule (C6H6). The symmetry of both systems determines the motions of the oscillators, i.e., the carbon atoms or the magnetic vortices. This allows to simplify the derivation of the fundamentally different dispersion relations depending on the previously tuned polarization state. The experiments confirm the calculations and prove that the magnetic vortex molecule features a reprogrammable band structure or dispersion relation. Consequently, this work allows further research studies to tailor the characteristic properties of various magnetic vortex arrangements by tuning the polarization state. Consequently, this work allows further research studies to tailor the characteristic properties of various magnetic vortex arrangements by tuning the polarization state. Das Zusammenspiel einer Vielzahl gleichartiger, gut verstandener Bausteine spielt eine entscheidende Rolle in vielen komplexen Systemen verschiedenster wissenschaftlicher Disziplinen wie Biochemie, Photonik, Ingenieurswissenschaften oder Nanoelektronik. Zum Beispiel bestimmen periodische Anordnungen von Atomen oder Molekulen die physikalischen Eigenschaften von Kristallen. In dieser Arbeit werden magnetisch wechselwirkende Wirbel, sogenannte magnetische Vortizes, zu magnonischen Kristallen angeordnet. Die verwendete Elektronenstrahl-Lithographie erlaubt es, die Vortizes mit Nanometer-Prazision herzustellen und als Basis auf einer regelmassigen Kristallstruktur zu platzieren. Mittels zeitaufgeloster Rontgenmikroskopie am MAXYMUS Mikroskop (BESSY II Synchrotron, Helmholtz-Zentrum Berlin) ist es moglich, die dynamischen Prozesse mit einer Zeitauflosung von unter einer Nanosekunde und gleichzeitiger ortlicher Auflosung auf der Nanometer-Skala abzubilden. In den Experimenten wird ein hochfrequentes magnetisches Anregungsfeld adiabatisch reduziert. Dies fuhrt zu einer selbstorganisierten Einstellung der Polarisationen der Vortizes im Kristall. Trotz der Komplexitat der untersuchten Systeme erzeugen die lokalen Interaktionen eine globale Ordnung in Form von hochsymmetrischen Polarisationszustanden. Diese hangen von der Anregungsfrequenz und der Starke der hauptsachlich dipolaren magnetischen Wechselwirkung der Vortizes ab. Zur Beschreibung der experimentellen Ergebnisse wird ein analytisches Model entwickelt und numerisch geloste Bewegungsgleichungen werden untersucht. Die selbstorganisiert eingestellten Polarisationszustande konnen daraufhin mit einem elementaren Stabilitatskriterium erklart werden, das auf der Anregbarkeit von Eigenmoden im Kristall basiert. Weitere Messungen mit ferromagnetischer Absorptionsspektroskopie erlauben es, die deutlichen Einflusse der selbstorganisierten Zustandseinstellung auf die charakteristischen Frequenzen der Vortex-Bewegungen zu studieren. Diese Einflusse werden weiter in Experimenten an ringartigen Anordnungen von Vortizes, die starke Ahnlichkeit zum Molekul Benzol (C6H6) haben, untersucht. Bei beiden Systemen bestimmt die Symmetrie die Bewegung der Oszillatoren, das heist der Kohlenstoffatome beziehungsweise der magnetischen Vortizes. Dies erlaubt es auf vereinfachte Weise in einem analytischen Dipol-Model die Dispersionsrelation des Vortex-Molekuls herzuleiten, die stark vom vorherrschenden Polarisationszustand abhangt. In den Experimenten wird die Polarisationsabhangigkeit bestatigt und somit gezeigt, dass das magnetische Vortex-Molekul eine einstellbare Bandstruktur beziehungsweise Dispersionsrelation aufweist. Infolgedessen erlaubt es diese Arbeit weiterfuhrenden Studien die charakteristischen Eigenschaften vielfaltiger Anordnungen magnetischer Vortizes gezielt zu manipulieren und maszuschneidern.

A strong bias asymmetry of the spin-injection efficiency through an epitaxial Fe/GaAs Schottky tunnel contact is observed. Low-temperature post-growth thermal annealing is shown to strongly affect the spin-injection efficiency. The annealing leads either to a reduction or an enhancement. The spin accumulation is addressed electrically in a lateral spin-valve geometry using a non-local spin-valve setup at liquid helium temperatures. A spin-injection efficiency of up to 5.5% is estimated from experimental results. The electrical properties of the Schottky tunnel diode do not reflect the bias asymmetry and the changes in the spin-injection efficiency during annealing. Formation of spin-polarized interface states (IS) close to the Fermi-level is a possible explanation. The IS will not only radically affect the spin-injection but also the spin-detection process.

We study the magnetization dynamics of coupled vortices in arrays of Permalloy disks via analytical calculations and scanning transmission x-ray microscopy. The Thiele approach is used to derive linear equations of motion of the vortices. Thereby, vortex motions following a nanosecond field pulse are described by a superposition of eigenmodes that depend on the vortex polarizations. Eigenmodes are calculated for a specific polarization pattern of a 3 × 3 vortex array. With magnetic field pulses distinct oscillations are excited and imaged in space and time. The calculated eigenmodes precisely describe the measured oscillations.