We analyze the current experimental and theoretical research about the magnetization (Barkhausen) noise in magnetic thin films. We observe that, in respect to three-dimensional systems, the situation is much more complicated, and many details still have to be analyzed and understood. In particular, the critical exponents must be correctly analyzed when compared with the theoretical predictions. We observe, for instance, that the easured magnetization steps in optical measurements do not actually correspond to the avalanche size, as claimed, but to a different quantity having a different critical exponent. We also observe as the lack of a significative demagnetizing field does not assure to have a stationary Barkhausen signal, which again implies a different set of exponents. For comparison, we report in detail all the possible theoretical values of the critical exponents calculated for a single DW model.
We experimentally investigate the average shapes of magnetization avalanches with the goal to understand the origin of their time asymmetry. We performed measurements on amorphous and polycrystalline magnetic materials, showing that the asymmetry can depend on several parameters, such as the applied field rate, and the duration and size of the avalanche itself. We suggest, as a possible explanation, to investigate the effect of the eddy currents on the measured signal.
Since its discovery by Barkhausen in 1919, the jerky motion of domain walls in bulk soft magnetic materials has represented a unique tool to study the microscopical processes responsible for the magnetic hysteresis. For long time, the description of this complex motion has been purely phenomenological, without any precise connection with the magnetization processes involved or the material microstructure. In the last years, using different approaches proper of mechanical statistics, new microscopical models has been introduced, offering the possibility to link the observed statistical properties of the noise to some material parameters. In particular, the Barkhausen jumps are found to exhibit universal properties, with the size and duration distributions showing extended scaling regions. Moreover, the properties of the noise of different materials can be grouped into two universality classes, depending only on the strength of long range interactions. We review all these aspects and peculiarities of the recent studies, with a particular emphasis of the still existing differences between the available experimental data and the theoretical predictions. We also show how this approach is useful to investigate the general properties of magnetic hysteresis, and the dynamics of domain walls in thin films, an important technological open problem strongly debated in the recent literature.
Conference Committee Involvement (4)
Noise and Fluctuations in Circuits, Devices, and Materials
21 May 2007 | Florence, Italy
Fluctuations and Noise in Materials II
24 May 2005 | Austin, Texas, United States
Fluctuations and Noise in Materials
26 May 2004 | Maspalomas, Gran Canaria Island, Spain