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Barkhausen effect
The magnetic Barkhausen effect, (also called Barkhausen jumps), was first detected in 1917 by the German physicist Heinrich Georg Barkhausen. He describes the discontinuous change in the magnetization of ferromagnetic materials, which are in a constantly changing, external magnetic field. Barkhausen was able to identify the effect named after him by means of acoustic signals, which is why one speaks of the so-called Barkhausen sough.
What is the Barkhausen effect?
In ferromagnetic materials, are many small elementary magnets, those are areas, which are characterized by a uniform direction of magnetization: the so-called Weiss districts. The Bloch walls separate these.
If the field strength of the external magnetic field is slowly increased, the magnetization of the material does not increase in a continuous curve, but in jumps, the Barkhausen jumps. In the first step, the Bloch walls shift and jump from one lattice defect (irregularities in a periodic crystal lattice) to the next. When the field strength is further enhanced, the magnetic moments of complete Weiss districts flip over and merge with each other. The magnetization curve is more like a staircase curve. The sudden changes can be made audible through an experiment (Barkhausen effect).
How does the experiment to prove the Barkhausen effect work?
A sample surrounded by a coil is moved into a changing magnetic field. To the induction coil, headphones or an amplifier with speaker are connected. With the successive, sudden changes in the magnetization in the material, a small current is measurable each time (depending on the size of the Weiss district, which has changed its direction).
If the amplifier detects these Barkhausen jumps, a slight crackling or noise is heard. In addition, the Barkhausen effect can also be visualized via an oscilloscope.