Institute for Complex Systems - Sapienza - CNR

  • Full Screen
  • Wide Screen
  • Narrow Screen
  • Increase font size
  • Default font size
  • Decrease font size
ISC Sapienza Hysteresis

Hysteresis

Research on hysteresis and random magnets

Publications >>

Fractures and crack propagation

E-mail Print PDF

The intermittent and self-similar fluctuations displayed by a slow crack
during the propagation in a heterogeneous medium can be quantitatively described by an
extension of a classical statistical model for fracture. The model yields the correct dynamical
and morphological scaling, and allows to demonstrate that the scale invariance originates
from the presence of a non-equilibrium, reversible, critical transition which, in the presence
of dissipation, gives rise to self-organized critical behaviour.

G Pontuale, F Colaiori, A Petri (2013), Slow crack propagation through a disordered medium: Critical transition and dissipation, EPL 101, 2013.

Last Updated on Sunday, 16 November 2014 11:48

Disorder driven non-equilibrium phase transition: the Random field Ising model

E-mail Print PDF

In hard magnetic materials, the domain walls movement or even creation is suppressed, and other mechanisms, like domains nucleation and coherent spin rotation enter in the process of magnetization reversal. For these kind of materials a description in terms of spin models is more appropriate. We focused on the non-equilibrium properties of the random field Ising model (RFIM), to describe the competition between quenched disorder and exchange interactions and their effect on the hysteretic behavior.

Last Updated on Sunday, 16 November 2014 12:41 Read more...

Dynamic hysteresis in thin and ultra-thin films

E-mail Print PDF

The physics of thin and ultra-thin magnetic films has been extensively studied in the recent past, because of its important implications for applications to high frequency devices. Power losses in ferromagnetic materials generally depend on the frequency of the applied field, a phenomenon referred to as dynamic hysteresis. The problem has great importance from a purely theoretical point of view, for the understanding of the dynamics of disordered magnetic systems, which represents a central issue in non–equilibrium statistical mechanics. While dynamic hysteresis in metallic bulk three dimensional systems is well understood in terms of eddy current dissipation, a satisfying theory for thin films, where the effect of eddy current is expected to become negligible, is still lacking. Hence, in recent years a great attention, both experimental and theoretical has been devoted to magnetic reversal in thin and ultra-thin ferromagnetic films.

Last Updated on Sunday, 16 November 2014 11:46 Read more...

Crackling noise: the Barkhausen effect

E-mail Print PDF

The term “crackling noise” refers to the signal that some disordered systems produce as a response to an external driving field smoothly changing in time. Due to the presence of disorder, crackling signals are extremely irregular, despite the steady increase of the external forcing. They are typically characterized by a sequence of pulses of very different sizes and durations, separated by quiescence intervals. Tiny events occur very frequently, while large ones are rare, with power laws probability distributions.

Systems that “crackle” are found in many different situations, and, remarkably, the corresponding signals often share some common characteristic features. Examples of crackling signals include the shear response of a granular media, the acoustic emission during martensitic phase transitions, the bursts of dislocations activity in plastic deformation, the dynamic of superconductors and superfluids, the fluctuations in the stock market, the dielectric polarization of ferroelectric materials, the acoustic emission in fractures, and the seismic activity in earthquakes. Crackling noise signals are expected to encode information on the physical process that generates them. Understanding the statistical properties of these jerky emissions, is therefore a step towards the understanding of the microscopic dynamics taking place in the system that crackles. Moreover, the fact that very diverse systems behave in a remarkably similar manner, suggests that some general basic principle may exist in the underlying physics.

 

Last Updated on Sunday, 16 November 2014 11:47 Read more...