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Classical Barkhausen noises have been known in magnetic systems for over a hundred years, but until now no one had observed this phenomenon in the quantum world. Physicists from the USA and Canada developed and conducted experiments with crystalline material, yttrium and lithium fluoride, doped with holmium. And they witnessed the largest macroscopic quantum phenomenon in laboratory conditions - quantum tunneling of a huge number of magnetic spins.
In the presence of a magnetic field, all spins, or magnetic moments, of electrons in ferromagnetic materials line up in one direction - but not all at once. It happens gradually, from domain to domain, which affect each other like an avalanche. One way to notice this change is to listen. In 1919, the physicist Heinrich Barkhausen wrapped a wire around a magnet and brought it to a loudspeaker and distinguished the crackling sound caused by the cracking of the blast furnace walls. A similar phenomenon can be observed in other systems, such as earthquakes and photomultipliers, writes Physics World.
In principle, the effects of quantum mechanics can also create Barkhausen noises. In this version, the change in spin occurs when the particles fly through the energy barrier instead of jumping over it. This phenomenon is called quantum tunneling. Physicists from the California Institute of Technology and the University of British Columbia observed quantum Brackhausen noise in a crystalline quantum magnet cooled to -273 degrees Celsius. And instead of noticeable noise, scientists measured voltage spikes when the spins changed orientation.
When spin groups in different domains flipped, the Barkhausen noises looked like a series of voltage spikes. The researchers attributed these jumps to quantum effects because they were unaffected by the 600% increase in temperature. Otherwise, changes would occur in the classic mode. In addition, the application of a magnetic field perpendicular to the spin axes had an extremely strong effect: the field began to behave like a quantum "knot" in the material.
This, according to scientists, is another proof of the new quantum nature of Barkhausen noise. Now the team of physicists plans to apply the method to non-magnetic materials. Perhaps this combined macroscopic and quantum phenomenon can occur everywhere.
