9 research outputs found
Random-Manifold to Random-Periodic Depinning of an Elastic Interface
We study numerically the depinning transition of driven elastic interfaces in
a random-periodic medium with localized periodic-correlation peaks in the
direction of motion. The analysis of the moving interface geometry reveals the
existence of several characteristic lengths separating different length-scale
regimes of roughness. We determine the scaling behavior of these lengths as a
function of the velocity, temperature, driving force, and transverse
periodicity. A dynamical roughness diagram is thus obtained which contains, at
small length scales, the critical and fast-flow regimes typical of the
random-manifold (or domain wall) depinning, and at large length-scales, the
critical and fast-flow regimes typical of the random-periodic (or
charge-density wave) depinning. From the study of the equilibrium geometry we
are also able to infer the roughness diagram in the creep regime, extending the
depinning roughness diagram below threshold. Our results are relevant for
understanding the geometry at depinning of arrays of elastically coupled thin
manifolds in a disordered medium such as driven particle chains or vortex-line
planar arrays. They also allow to properly control the effect of transverse
periodic boundary conditions in large-scale simulations of driven disordered
interfaces.Comment: 19 pages, 10 figure
Thermal rounding exponent of the depinning transition of an elastic string in a random medium
We study numerically thermal effects at the depinning transition of an
elastic string driven in a two-dimensional uncorrelated disorder potential. The
velocity of the string exactly at the sample critical force is shown to behave
as , with the thermal rounding exponent. We show that the
computed value of the thermal rounding exponent, , is robust and
accounts for the different scaling properties of several observables both in
the steady-state and in the transient relaxation to the steady-state. In
particular, we show the compatibility of the thermal rounding exponent with the
scaling properties of the steady-state structure factor, the universal
short-time dynamics of the transient velocity at the sample critical force, and
the velocity scaling function describing the joint dependence of the
steady-state velocity on the external drive and temperature
Thermal rounding of the depinning transition
We study thermal effects at the depinning transition by numerical simulations
of driven one-dimensional elastic interfaces in a disordered medium. We find
that the velocity of the interface, evaluated at the critical depinning force,
can be correctly described with the power law , where is
the thermal exponent. Using the sample-dependent value of the critical force,
we precisely evaluate the value of directly from the temperature
dependence of the velocity, obtaining the value . By
measuring the structure factor of the interface we show that both the
thermally-rounded and the T=0 depinning, display the same large-scale geometry,
described by an identical divergence of a characteristic length with the
velocity , where and are respectively
the T=0 correlation and depinning exponents. We discuss the comparison of our
results with previous estimates of the thermal exponent and the direct
consequences for recent experiments on magnetic domain wall motion in
ferromagnetic thin films.Comment: 6 pages, 3 figure
Thermal rounding of the depinning transition in ultrathin Pt/Co/Pt films
We perform a scaling analysis of the mean velocity of extended magnetic
domain walls driven in ultrathin Pt/Co/Pt ferromagnetic films with
perpendicular anisotropy, as a function of the applied external field for
different film-thicknesses. We find that the scaling of the experimental data
around the thermally rounded depinning transition is consistent with the
universal depinning exponents theoretically expected for elastic interfaces
described by the one-dimensional quenched Edwards-Wilkinson equation. In
particular, values for the depinning exponent and thermal rounding
exponent are tested and the present analysis of the experimental data is
compatible with and , in agreement with numerical
simulations.Comment: 8 pages, 8 figure
Pinning dependent field driven domain wall dynamics and thermal scaling in an ultrathin Pt/Co/Pt magnetic film
Magnetic field-driven domain wall motion in an ultrathin Pt/Co(0.45nm)/Pt
ferromagnetic film with perpendicular anisotropy is studied over a wide
temperature range. Three different pinning dependent dynamical regimes are
clearly identified: the creep, the thermally assisted flux flow and the
depinning, as well as their corresponding crossovers. The wall elastic energy
and microscopic parameters characterizing the pinning are determined. Both the
extracted thermal rounding exponent at the depinning transition, 0.15,
and the Larkin length crossover exponent, 0.24, fit well with the
numerical predictions.Comment: 5 pages, 4 figure
Maximum relative height of elastic interfaces in random media
The distribution of the maximal relative height (MRH) of self-affine
one-dimensional elastic interfaces in a random potential is studied. We analyze
the ground state configuration at zero driving force, and the critical
configuration exactly at the depinning threshold, both for the random-manifold
and random-periodic universality classes. These configurations are sampled by
exact numerical methods, and their MRH distributions are compared with those
with the same roughness exponent and boundary conditions, but produced by
independent Fourier modes with normally distributed amplitudes. Using Pickands'
theorem we derive an exact analytical description for the right tail of the
latter. After properly rescaling the MRH distributions we find that corrections
from the Gaussian independent modes approximation are in general small, as
previously found for the average width distribution of depinning
configurations. In the large size limit all corrections are finite except for
the ground-state in the random-periodic class whose MRH distribution becomes,
for periodic boundary conditions, indistinguishable from the Airy distribution.
We find that the MRH distributions are, in general, sensitive to changes of
boundary conditions.Comment: 14 pages, 10 figure