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

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.

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 $\tau_{a}=1.5$. We derive a scaling relation $\tau_a=2\tau-1$ between the local cluster exponent $\tau_a$ and the global avalanche exponent $\tau$. 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

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

Barkhausen noise from zigzag domain walls

We investigate the Barkhausen noise in ferromagnetic thin films with zigzag domain walls. We use a cellular automaton model that describes the motion of a zigzag domain wall in an impure ferromagnetic quasi-two dimensional sample with in-plane uniaxial magnetization at zero temperature, driven by an external magnetic field. The main ingredients of this model are the dipolar spin-spin interactions and the anisotropy energy. A power law behavior with a cutoff is found for the probability distributions of size, duration and correlation length of the Barkhausen avalanches, and the critical exponents are in agreement with the available experiments. The link between the size and the duration of the avalanches is analyzed too, and a power law behavior is found for the average size of an avalanche as a function of its duration.Comment: 11 pages, 12 figure

Protein accumulation in the endoplasmic reticulum as a non-equilibrium phase transition

Several neurological disorders are associated with the aggregation of aberrant proteins, often localized in intracellular organelles such as the endoplasmic reticulum. Here we study protein aggregation kinetics by mean-field reactions and three dimensional Monte carlo simulations of diffusion-limited aggregation of linear polymers in a confined space, representing the endoplasmic reticulum. By tuning the rates of protein production and degradation, we show that the system undergoes a non-equilibrium phase transition from a physiological phase with little or no polymer accumulation to a pathological phase characterized by persistent polymerization. A combination of external factors accumulating during the lifetime of a patient can thus slightly modify the phase transition control parameters, tipping the balance from a long symptomless lag phase to an accelerated pathological development. The model can be successfully used to interpret experimental data on amyloid-\b{eta} clearance from the central nervous system

Avalanche precursors of failure in hierarchical fuse networks

We study precursors of failure in hierarchical random fuse network models which can be considered as idealizations of hierarchical (bio)materials where fibrous assemblies are held together by multi-level (hierarchical) cross-links. When such structures are loaded towards failure, the patterns of precursory avalanche activity exhibit generic scale invariance: Irrespective of load, precursor activity is characterized by power-law avalanche size distributions without apparent cut-off, with power-law exponents that decrease continuously with increasing load. This failure behavior and the ensuing super-rough crack morphology differ significantly from the findings in non-hierarchical structures

Dynamic hysteresis from zigzag domain walls

We investigate dynamic hysteresis in ferromagnetic thin films with zigzag domain walls. We introduce a discrete model describing the motion of a wall in a disordered ferromagnet with in-plane magnetization, driven by an external magnetic field, considering the effects of dipolar interactions and anisotropy. We analyze the effects of external field frequency and temperature on the coercive field by Monte Carlo simulations, and find a good agreement with the experimental data reported in literature for Fe/GaAs films. This implies that dynamic hysteresis in this case can be explained by a single propagating domain wall model without invoking domain nucleation.Comment: 10 pages, 13 figures; minor modifications and two figures adde

Comment on ``Self-organized criticality and absorbing states: Lessons from the Ising model"

According to Pruessner and Peters [Phys. Rev. E {\bf 73}, 025106(R) (2006)], the finite size scaling exponents of the order parameter in sandpile models depend on the tuning of driving and dissipation rates with system size. We point out that the same is not true for {\em avalanches} in the slow driving limit.Comment: 3 pages, 1 figure, to appear in Phys. Rev.