arXiv subjects

Frank Schulz

Publications and source records attributed to Frank Schulz.

5 recordsLinked to original sources

arXiv2026

Direct observation of propagating spin waves in a spin-Hall nano-oscillator

Constriction-based spin Hall nano-oscillators (SHNOs) show great promise for application as highly tunable microwave sources with straightforward scalability toward large coupled networks. However, details of the magnetization dynamics within SHNOs have thus far not been addressed experimentally, due to the minute time and length scales involved. In this work, we present direct imaging of the magnetization dynamics within a single CoFeB-based SHNO using time-resolved scanning transmission X-ray microscopy (STXM). Our measurements reveal that the magnon amplitude is the strongest at the two constriction edges, with a pronounced assymetry favoring one edge, and that emitted spin waves exhibit strongly anisotropic propagation. Micromagnetic simulations suggest that grain boundaries and the Dzyaloshinskii-Moriya interaction (DMI) play a key role in both effects. Furthermore, the magnetodynamics changed during the measurement, indicating that the CoFeB/MgO interface may be more susceptible to X-ray induced modifications than previously recognized, challenging its presumed radiation hardness.

cond-mat.mes-hall↗

arXiv2024

The Effect of Ga-Ion Irradiation on Sub-Micron-Wavelength Spin Waves in Yttrium-Iron-Garnet Films

We investigate the effect of focused-ion-beam (FIB) irradiation on spin waves with sub-micron wavelengths in Yttrium-Iron-Garnet (YIG) films. Time-resolved scanning transmission X-ray (TR-STXM) microscopy was used to image the spin waves in irradiated regions and deduce corresponding changes in the magnetic parameters of the film. We find that the changes of Ga$^+$ irradiation can be understood by assuming a few percent change in the effective magnetization $M_\mathrm{eff}$ of the film due to a trade-off between changes in anisotropy and effective film thickness. Our results demonstrate that FIB irradiation can be used to locally alter the dispersion relation and the effective refractive index $n_\textrm{eff}$ of the film, even for submicron wavelengths. To achieve the same change in $n_\textrm{eff}$ for shorter wavelengths, a higher dose is required, but no significant deterioration of spin wave propagation length in the irradiated regions was observed, even at the highest applied doses.

physics.app-ph↗

arXiv2020

Towards an Integrated Platform for Big Data Analysis

The amount of data in the world is expanding rapidly. Every day, huge amounts of data are created by scientific experiments, companies, and end users' activities. These large data sets have been labeled as "Big Data", and their storage, processing and analysis presents a plethora of new challenges to computer science researchers and IT professionals. In addition to efficient data management, additional complexity arises from dealing with semi-structured or unstructured data, and from time critical processing requirements. In order to understand these massive amounts of data, advanced visualization and data exploration techniques are required. Innovative approaches to these challenges have been developed during recent years, and continue to be a hot topic for re-search and industry in the future. An investigation of current approaches reveals that usually only one or two aspects are ad-dressed, either in the data management, processing, analysis or visualization. This paper presents the vision of an integrated plat-form for big data analysis that combines all these aspects. Main benefits of this approach are an enhanced scalability of the whole platform, a better parameterization of algorithms, a more efficient usage of system resources, and an improved usability during the end-to-end data analysis process.

cs.DB↗

arXiv2020

Efficient Route Planning with Temporary Driving Bans, Road Closures, and Rated Parking Areas

We study the problem of planning routes in road networks when certain streets or areas are closed at certain times. For heavy vehicles, such areas may be very large since many European countries impose temporary driving bans during the night or on weekends. In this setting, feasible routes may require waiting at parking areas, and several feasible routes with different trade-offs between waiting and driving detours around closed areas may exist. We propose a novel model in which driving and waiting are assigned abstract costs, and waiting costs are location-dependent to reflect the different quality of the parking areas. Our goal is to find Pareto-optimal routes with regards to arrival time at the destination and total cost. We investigate the complexity of the model and determine a necessary constraint on the cost parameters such that the problem is solvable in polynomial time. We present a thoroughly engineered implementation and perform experiments on a production-grade real world data set. The experiments show that our implementation can answer realistic queries in around a second or less which makes it feasible for practical application.

cs.DS↗

arXiv2012

Positive topological entropy for multi-bump magnetic fields

We study the dynamics of a charged particle in a planar magnetic field which consists of $n\geq 2$ disjoint localized peaks. We show that, under mild geometric conditions, this system is semi-conjugated to the full shift on $n$ symbols and, hence, carries positive topological entropy.

math.DS↗