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Lasse Laurson

Publications and source records attributed to Lasse Laurson.

63 records · Page 4Linked to original sources
arXiv2009

Effect of dipolar interactions for domain wall dynamics in magnetic thin films

We study the effect of long range dipolar forces on the dynamics and morphology of domain walls in magnetic thin films by numerical simulations of the spin-1 random field Ising model. By studying the size distribution of avalanches of domain wall motion arising as a response to quasistatic external driving, we observe a cross-over from the case dominated by short range interactions to another universality class where the long range dipolar forces become important. This crossover is accompanied with a change of the domain wall morphology from a rough wall to walls with zigzag structure.

cond-mat.mtrl-sci↗
arXiv2009

Modeling domain wall dynamics in thin magnetic strips with disorder

We present a line-based model of transverse domain walls in thin magnetic strips, to study the effect of bulk disorder on the domain wall dynamics within the thermally activated creep regime. The creep velocity is found to exhibit a non-linear dependence on both applied magnetic fields and electric currents, characterized by similar creep exponents for both forms of the external drive. We discuss briefly the significance of the inherently stochastic thermally activated domain wall motion from the point of view of spintronics applications, where it generally is essential to be able to control the domain wall displacement in a deterministic manner.

cond-mat.mtrl-sci↗
arXiv2008

The effect of thresholding on temporal avalanche statistics

We discuss intermittent time series consisting of discrete bursts or avalanches separated by waiting or silent times. The short time correlations can be understood to follow from the properties of individual avalanches, while longer time correlations often present in such signals reflect correlations between triggerings of different avalanches. As one possible source of the latter kind of correlations in experimental time series, we consider the effect of a finite detection threshold, due to e.g. experimental noise that needs to be removed. To this end, we study a simple toy model of an avalanche, a random walk returning to the origin or a Brownian bridge, in the presence and absence of superimposed delta-correlated noise. We discuss the properties after thresholding of artificial timeseries obtained by mixing toy avalanches and waiting times from a Poisson process. Most of the resulting scalings for individual avalanches and the composite timeseries can be understood via random walk theory, except for the waiting time distributions when strong additional noise is added. Then, to compare with a more complicated case we study the Manna sandpile model of self-organized criticality, where some further complications appear.

cond-mat.stat-mech↗
arXiv2008

Driven particle in a cloud of mobile impurities

The dynamics of a test particle interacting with diffusing impurities in one dimension is investigated analytically and numerically. In the absence of an applied external force, the dynamics of the particle can be characterized by a distribution of monotonic excursions $Δx$, which scales as a power law with an exponent $τ_{Δx} = 4/3$. When the particle is driven at a slow constant velocity, there is again a power law distribution for the monotonic changes of the force $ΔF$, which is characterized by a similar exponent $τ_{ΔF}=4/3$. These results can be understood from the theory of random walks.

cond-mat.stat-mech↗
arXiv2008

Dislocation interactions mediated by grain boundaries

The dynamics of dislocation assemblies in deforming crystals indicate the emergence of collective phenomena, intermittent fluctuations and strain avalanches. In polycrystalline materials, the understanding of plastic deformation mechanisms depends on grasping the role of grain boundaries on dislocation motion. Here the interaction of dislocations and elastic, low angle grain boundaries is studied in the framework of a discrete dislocation representation. We allow grain boundaries to deform under the effect of dislocation stress fields and compare the effect of such a perturbation to the case of rigid grain boudaries. We are able to determine, both analytically and numerically, corrections to dislocation stress fields acting on neighboring grains, as mediated by grain boundary deformation. Finally, we discuss conclusions and consequences for the avalanche statistics, as observed in polycrystalline samples.

cond-mat.mtrl-sci↗
arXiv2006

Fluctuations in fluid invasion into disordered media

Interfaces moving in a disordered medium exhibit stochastic velocity fluctuations obeying universal scaling relations related to the presence or absence of conservation laws. For fluid invasion of porous media, we show that the fluctuations of the velocity are governed by a geometry-dependent length scale arising from fluid conservation. This result is compared to the statistics resulting from a non-equilibrium (depinning) transition between a moving interface and a stationary, pinned one.

cond-mat.dis-nn↗
arXiv2006

$1/f$ noise and avalanche scaling in plastic deformation

We study the intermittency and noise of dislocation systems undergoing shear deformation. Simulations of a simple two-dimensional discrete dislocation dynamics model indicate that the deformation rate exhibits a power spectrum scaling of the type $1/f^α$. The noise exponent is far away from a Lorentzian, with $α\approx 1.5$. This result is directly related to the way the durations of avalanches of plastic deformation activity scale with their size.

cond-mat.stat-mech↗
arXiv2005

Power spectra of self-organized critical sandpiles

We analyze the power spectra of avalanches in two classes of self-organized critical sandpile models, the Bak-Tang-Wiesenfeld model and the Manna model. We show that these decay with a $1/f^α$ power law, where the exponent value $α$ is significantly smaller than 2 and equals the scaling exponent relating the avalanche size to its duration. We discuss the basic ingredients behind this result, such as the scaling of the average avalanche shape.

cond-mat.stat-mech↗