632 research outputs found
Barkhausen noise in soft amorphous magnetic materials under applied stress
We report experimental measurements of Barkhausen noise on
Fe_{64}Co_{21}B_{15} amorphous alloy under tensile stress. We interpret the
scaling behavior of the noise distributions in terms of the depinning
transition of the domain walls. We show that stress induced anisotropy enhance
the effect of short-range elastic interactions that dominate over long-range
dipolar interactions. The universality class is thus different from the one
usually observed in Barkhausen noise measurements and is characterized by the
exponents \tau = 1.3 and \alpha = 1.5, for the decay of the distributions of
jump sizes and durations.Comment: 6 pages, 3 .eps figures. Submitted to the 43rd Magnetism and Magnetic
Materials Conference (J. Appl. Phys.
Hysteresis and noise in ferromagnetic materials with parallel domain walls
We investigate dynamic hysteresis and Barkhausen noise in ferromagnetic
materials with a huge number of parallel and rigid Bloch domain walls.
Considering a disordered ferromagnetic system with strong in-plane uniaxial
anisotropy and in-plane magnetization driven by an external magnetic field, we
calculate the equations of motion for a set of coupled domain walls,
considering the effects of the long-range dipolar interactions and disorder. We
derive analytically an expression for the magnetic susceptivity, related to the
effective demagnetizing factor, and show that it has a logarithmic dependence
on the number of domains. Next, we simulate the equations of motion and study
the effect of the external field frequency and the disorder on the hysteresis
and noise properties. The dynamic hysteresis is very well explained by means of
the loss separation theory.Comment: 13 pages, 11 figure
The role of stationarity in magnetic crackling noise
We discuss the effect of the stationarity on the avalanche statistics of
Barkhuasen noise signals. We perform experimental measurements on a
FeB amorphous ribbon and compare the avalanche distributions
measured around the coercive field, where the signal is stationary, with those
sampled through the entire hysteresis loop. In the first case, we recover the
scaling exponents commonly observed in other amorphous materials (,
). while in the second the exponents are significantly larger
(, ). We provide a quantitative explanation of the
experimental results through a model for the depinning of a ferromagnetic
domain wall. The present analysis shed light on the unusually high values for
the Barkhausen noise exponents measured by Spasojevic et al. [Phys. Rev. E 54
2531 (1996)].Comment: submitted to JSTAT. 11 pages 5 figure
On the power spectrum of magnetization noise
Understanding the power spectrum of the magnetization noise is a long
standing problem. While earlier work considered superposition of 'elementary'
jumps, without reference to the underlying physics, recent approaches relate
the properties of the noise with the critical dynamics of domain walls. In
particular, a new derivation of the power spectrum exponent has been proposed
for the random-field Ising model. We apply this approach to experimental data,
showing its validity and limitations.Comment: 8 pages, 3 .eps figures (elsart.cls style required
Universality classes and crossover scaling of Barkhausen noise in thin films
We study the dynamics of head-to-head domain walls separating in-plane
domains in a disordered ferromagnetic thin film. The competition between the
domain wall surface tension and dipolar interactions induces a crossover
between a rough domain wall phase at short length-scales and a large-scale
phase where the walls display a zigzag morphology. The two phases are
characterized by different critical exponents for Barkhausen avalanche dynamics
that are in quantitative agreement with experimental measurements on MnAs thin
films.Comment: 5 pages, 5 figure
Avalanches and clusters in planar crack front propagation
We study avalanches in a model for a planar crack propagating in a disordered
medium. Due to long-range interactions, avalanches are formed by a set of
spatially disconnected local clusters, the sizes of which are distributed
according to a power law with an exponent . We derive a scaling
relation between the local cluster exponent and the
global avalanche exponent . For length scales longer than a cross-over
length proportional to the Larkin length, the aspect ratio of the local
clusters scales with the roughness exponent of the line model. Our analysis
provides an explanation for experimental results on planar crack avalanches in
Plexiglas plates, but the results are applicable also to other systems with
long-range interactions.Comment: 7 pages, 6 figures, accepted for publication in Physical Review
The effect of disorder on transverse domain wall dynamics in magnetic nanostrips
We study the effect of disorder on the dynamics of a transverse domain wall
in ferromagnetic nanostrips, driven either by magnetic fields or spin-polarized
currents, by performing a large ensemble of GPU-accelerated micromagnetic
simulations. Disorder is modeled by including small, randomly distributed
non-magnetic voids in the system. Studying the domain wall velocity as a
function of the applied field and current density reveals fundamental
differences in the domain wall dynamics induced by these two modes of driving:
For the field-driven case, we identify two different domain wall pinning
mechanisms, operating below and above the Walker breakdown, respectively,
whereas for the current-driven case pinning is absent above the Walker
breakdown. Increasing the disorder strength induces a larger Walker breakdown
field and current, and leads to decreased and increased domain wall velocities
at the breakdown field and current, respectively. Furthermore, for adiabatic
spin transfer torque, the intrinsic pinning mechanism is found to be suppressed
by disorder. We explain these findings within the one-dimensional model in
terms of an effective damping parameter increasing with the disorder
strength.Comment: 5 pages, 3 figure
Etude des réactions physico-chimiques à l'interface liquide physiologique/verre bioactif
rapport Janus 2004, responsable de stage : E. Jallo
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