The Barkhausen effect occurs during the magnetization process
of a ferromagnetic material. It is due to the jerky motion of
the Domain Walls, under a variable external field.
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These are some Domain Walls of an amorphous alloy, using the scanning electron microscope. Thanks to K.Zaveta |
The application of an external field acts as a pressure on
the wall, but because of the presence of defects, inclusions,
interactions with other domains, the motion has the typical random
shape you can see below. Sometime the wall is pinned by the defect,
sometime the field is high enough to make the wall move.
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| This is a simulation of the Barkhausen noise (see the other pages for real signals, sounds, and associated hysteresis loops) |
This is why you see avalanches, or what we call Barkhausen jumps. But, be careful, change the field slowly, otherwise all the jumps collapse in a continuous fluctuating signal.
This dynamics is typical of many complex systems, such as earthquakes, sandpiles, superconductors… have you ever heard something about the self-organized criticality of complex dynamical system? Well, the Barkhausen effect is a nice example to study it!
Other pages
Links to other pages of interest about this effect
