arXiv subjects

Christoph Schneider

Publications and source records attributed to Christoph Schneider.

4 recordsLinked to original sources

arXiv2021

Full angular dependence of the spin Hall and ordinary magnetoresistance in epitaxial antiferromagnetic NiO(001)/Pt thin films

We report the observation of the three-dimensional angular dependence of the spin Hall magnetoresistance (SMR) in a bilayer of the epitaxial antiferromagnetic insulator NiO(001) and the heavy metal Pt, without any ferromagnetic element. The detected angular-dependent longitudinal and transverse magnetoresistances are measured by rotating the sample in magnetic fields up to 11 T, along three orthogonal planes (xy-, yz- and xz-rotation planes, where the z-axis is orthogonal to the sample plane). The total magnetoresistance has contributions arising from both the SMR and ordinary magnetoresistance. The onset of the SMR signal occurs between 1 and 3 T and no saturation is visible up to 11 T. The three-dimensional angular dependence of the SMR can be explained by a model considering the reversible field-induced redistribution of magnetostrictive antiferromagnetic S- and T-domains in the NiO(001), stemming from the competition between the Zeeman energy and the elastic clamping effect of the non-magnetic MgO substrate. From the observed SMR ratio, we estimate the spin mixing conductance at the NiO/Pt interface to be greater than $2\times10^{14}$ $Ω^{-1}$ $m^{-2}$. Our results demonstrate the possibility to electrically detect the Néel vector direction in stable NiO(001) thin films, for rotations in the xy- and xz- planes. Moreover, we show that a careful subtraction of the ordinary magnetoresistance contribution is crucial to correctly estimate the amplitude of the SMR.

cond-mat.mtrl-sci↗

arXiv2018

Direct observation and rational design of nucleation behavior in addressable self-assembly

In order to optimize a self-assembly reaction, it is essential to understand the factors that govern its pathway. Here, we examine the influence of nucleation pathways in a model system for addressable, multicomponent self-assembly based on a prototypical 'DNA-brick' structure. By combining temperature-dependent dynamic light scattering and atomic force microscopy with coarse-grained simulations, we show how subtle changes in the nucleation pathway profoundly affect the yield of the correctly formed structures. In particular, we can increase the range of conditions over which self-assembly occurs by utilizing stable multi-subunit clusters that lower the nucleation barrier for assembling subunits in the interior of the structure. Consequently, modifying only a small portion of a structure is sufficient to optimize its assembly. Due to the generality of our coarse-grained model and the excellent agreement that we find with our experimental results, the design principles reported here are likely to apply generically to addressable, multicomponent self-assembly.

cond-mat.soft↗

arXiv2018

Spin transport in multilayer systems with fully epitaxial NiO thin films

We report on the generation and transport of thermal spin currents in fully epitaxial γ-Fe$_2$O$_3$/NiO(001)/Pt and Fe$_3$O$_4$/NiO(001)/Pt trilayers. A thermal gradient, perpendicular to the plane of the sample, generates a magnonic spin current in the ferrimagnetic maghemite (γ-Fe$_2$O$_3$) and magnetite (Fe$_3$O$_4$) thin films by means of the spin Seebeck effect. The spin current propagates across the epitaxial, antiferromagnetic insulating NiO layer, before being detected in the Pt layer by the inverse spin Hall effect. The transport of the spin signal is studied as a function of the NiO thickness, temperature and ferrimagnetic material where the spin current is generated. In epitaxial NiO grown on maghemite, the spin Seebeck signal decays exponentially as a function of the NiO thickness, with a spin-diffusion length for thermally-generated magnons of λ$_{MSDL}$ = $1.6 \pm 0.2$ nm, largely independent on temperature. We see no enhancement of the spin current signal as previously reported for certain temperatures and thicknesses of the NiO. In epitaxial NiO grown on magnetite, the temperature-averaged spin diffusion length is λ$_{MSDL}$ = $3.8 \pm 0.3$ nm, and we observe an enhancement of the spin signal when the NiO thickness is 0.8 nm, demonstrating that the growth conditions dramatically affect the spin transport properties of the NiO even for full epitaxial growth. In contrast to theoretical predictions for coherent spin transport, we do not see vastly different spin diffusion lengths between epitaxial and polycrystalline NiO layers.

cond-mat.mtrl-sci↗

arXiv2011

Model Checking of Boolean Process Models

In the field of Business Process Management formal models for the control flow of business processes have been designed since more than 15 years. Which methods are best suited to verify the bulk of these models? The first step is to select a formal language which fixes the semantics of the models. We adopt the language of Boolean systems as reference language for Boolean process models. Boolean systems form a simple subclass of coloured Petri nets. Their characteristics are low tokens to model explicitly states with a subsequent skipping of activations and arbitrary logical rules of type AND, XOR, OR etc. to model the split and join of the control flow. We apply model checking as a verification method for the safeness and liveness of Boolean systems. Model checking of Boolean systems uses the elementary theory of propositional logic, no modal operators are needed. Our verification builds on a finite complete prefix of a certain T-system attached to the Boolean system. It splits the processes of the Boolean system into a finite set of base processes of bounded length. Their behaviour translates to formulas from propositional logic. Our verification task consists in checking the satisfiability of these formulas. In addition we have implemented our model checking algorithm as a java program. The time needed to verify a given Boolean system depends critically on the number of initial tokens. Because the algorithm has to solve certain SAT-problems, polynomial complexity cannot be expected. The paper closes with the model checking of some Boolean process models which have been designed as Event-driven Process Chains.

cs.LO↗