1,266 research outputs found
Hysteresis, Avalanches, and Noise: Numerical Methods
In studying the avalanches and noise in a model of hysteresis loops we have
developed two relatively straightforward algorithms which have allowed us to
study large systems efficiently. Our model is the random-field Ising model at
zero temperature, with deterministic albeit random dynamics. The first
algorithm, implemented using sorted lists, scales in computer time as O(N log
N), and asymptotically uses N (sizeof(double)+ sizeof(int)) bits of memory. The
second algorithm, which never generates the random fields, scales in time as
O(N \log N) and asymptotically needs storage of only one bit per spin, about 96
times less memory than the first algorithm. We present results for system sizes
of up to a billion spins, which can be run on a workstation with 128MB of RAM
in a few hours. We also show that important physical questions were resolved
only with the largest of these simulations
Ising Dynamics with Damping
We show for the Ising model that is possible construct a discrete time
stochastic model analogous to the Langevin equation that incorporates an
arbitrary amount of damping. It is shown to give the correct equilibrium
statistics and is then used to investigate nonequilibrium phenomena, in
particular, magnetic avalanches. The value of damping can greatly alter the
shape of hysteresis loops, and for small damping and high disorder, the
morphology of large avalanches can be drastically effected. Small damping also
alters the size distribution of avalanches at criticality.Comment: 8 pages, 8 figures, 2 colum
Hysteresis and Avalanches in the Random Anisotropy Ising Model
The behaviour of the Random Anisotropy Ising model at T=0 under local
relaxation dynamics is studied. The model includes a dominant ferromagnetic
interaction and assumes an infinite anisotropy at each site along local
anisotropy axes which are randomly aligned. Two different random distributions
of anisotropy axes have been studied. Both are characterized by a parameter
that allows control of the degree of disorder in the system. By using numerical
simulations we analyze the hysteresis loop properties and characterize the
statistical distribution of avalanches occuring during the metastable evolution
of the system driven by an external field. A disorder-induced critical point is
found in which the hysteresis loop changes from displaying a typical
ferromagnetic magnetization jump to a rather smooth loop exhibiting only tiny
avalanches. The critical point is characterized by a set of critical exponents,
which are consistent with the universal values proposed from the study of other
simpler models.Comment: 40 pages, 21 figures, Accepted for publication in Phys. Rev.
Correlations of triggering noise in driven magnetic clusters
We show that the temporal fluctuations of the threshold driving
field , which triggers an avalanche in slowly driven disordered
ferromagnets with many domains, exhibit long-range correlations in space and
time. The probability distribution of the distance between {\it successive}
avalanches as well as the distribution of trapping times of domain wall at a
given point in space have fractal properties with the universal scaling
exponents. We show how these correlations are related to the scaling behavior
of Barkhausen avalanches occurring by magnetization reversal. We also suggest a
transport equation which takes into account the observed noise correlations.Comment: 7 pages, Revtex, 4 figure
Universal Pulse Shape Scaling Function and Exponents: A Critical Test for Avalanche Models applied to Barkhausen Noise
In order to test if the universal aspects of Barkhausen noise in magnetic
materials can be predicted from recent variants of the non-equilibrium zero
temperature Random Field Ising Model (RFIM), we perform a quantitative study of
the universal scaling function derived from the
Barkhausen pulse shape in simulations and experiment. Through data collapses
and scaling relations we determine the critical exponents and
in both simulation and experiment. Although we find agreement
in the critical exponents, we find differences between theoretical and
experimental pulse shape scaling functions as well as between different
experiments.Comment: 19 pages (in preprint format), 5 figures, 1 tabl
- …