256 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
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
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
A spring-block model for Barkhausen noise
A simple mechanical spring-block model is introduced for studying
magnetization phenomena and in particularly the Barkhausen noise. The model
captures and reproduces the accepted microscopic picture of domain wall
movement and pinning. Computer simulations suggest that this model is able to
reproduce the main characteristics of hysteresis loops and Barkhausen jumps. In
the thermodynamic limit the statistics of the obtained Barkhausen jumps follows
several scaling laws, in qualitative agreement with the experimental results.
The simplicity of the model and the invoked mechanical analogies makes it
attractive for computer simulations and pedagogical purposes.Comment: Revtex, 8 pages, 6 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
Loss separation for dynamic hysteresis in magnetic thin films
We develop a theory for dynamic hysteresis in ferromagnetic thin films, on
the basis of the phenomenological principle of loss separation. We observe
that, remarkably, the theory of loss separation, originally derived for bulk
metallic materials, is applicable to disordered magnetic systems under fairly
general conditions regardless of the particular damping mechanism. We confirm
our theory both by numerical simulations of a driven random--field Ising model,
and by re--examining several experimental data reported in the literature on
dynamic hysteresis in thin films. All the experiments examined and the
simulations find a natural interpretation in terms of loss separation. The
power losses dependence on the driving field rate predicted by our theory fits
satisfactorily all the data in the entire frequency range, thus reconciling the
apparent lack of universality observed in different materials.Comment: 4 pages, 6 figure
Wavelet transforms in a critical interface model for Barkhausen noise
We discuss the application of wavelet transforms to a critical interface
model, which is known to provide a good description of Barkhausen noise in soft
ferromagnets. The two-dimensional version of the model (one-dimensional
interface) is considered, mainly in the adiabatic limit of very slow driving.
On length scales shorter than a crossover length (which grows with the strength
of surface tension), the effective interface roughness exponent is
, close to the expected value for the universality class of the
quenched Edwards-Wilkinson model. We find that the waiting times between
avalanches are fully uncorrelated, as the wavelet transform of their
autocorrelations scales as white noise. Similarly, detrended size-size
correlations give a white-noise wavelet transform. Consideration of finite
driving rates, still deep within the intermittent regime, shows the wavelet
transform of correlations scaling as for intermediate frequencies.
This behavior is ascribed to intra-avalanche correlations.Comment: RevTeX, 10 pages, 9 .eps figures; Physical Review E, to be publishe
Signature of effective mass in crackling noise asymmetry
Crackling noise is a common feature in many dynamic systems [1-9], the most
familiar instance of which is the sound made by a sheet of paper when crumpled
into a ball. Although seemingly random, this noise contains fundamental
information about the properties of the system in which it occurs. One
potential source of such information lies in the asymmetric shape of noise
pulses emitted by a diverse range of noisy systems [8-12], but the cause of
this asymmetry has lacked explanation [1]. Here we show that the leftward
asymmetry observed in the Barkhausen effect [2] - the noise generated by the
jerky motion of domain walls as they interact with impurities in a soft magnet
- is a direct consequence of a magnetic domain wall's negative effective mass.
As well as providing a means of determining domain wall effective mass from a
magnet's Barkhausen noise our work suggests an inertial explanation for the
origin of avalanche asymmetries in crackling noise phenomena more generally.Comment: 13 pages, 4 figures, to appear in Nature Physic
Dynamic hysteresis in Finemet thin films
We performed a series of dynamic hysteresis measurements on three series of
Finemet films with composition FeCuNbSiB, using
both the longitudinal magneto-optical Kerr effect (MOKE) and the inductive
fluxometric method. The MOKE dynamic hysteresis loops show a more marked
variability with the frequency than the inductive ones, while both measurements
show a similar dependence on the square root of frequency. We analyze these
results in the frame of a simple domain wall depinning model, which accounts
for the general behavior of the data.Comment: 3 pages, 3 figure
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