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Pinning
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Pinning

Superconductivity's footprint

Contrary to the Meissner effect, it is “vortex pinning” which, in some cases, is responsible for the levitation of a magnet. While the Meissner effect expels the magnet from the superconductor when the latter is cooled, vortex pinning maintains the magnet where it was when the superconductor was cooled.

Experiment pinning by yourself !
Drag and drop the magnet on the superconductor pellet and cool down with liquid nitrogen : the magnet is pinned ! You can also use a block to pin the magnet over the floor (remove the block after cooling). Note that if the pallet is already cool, you won't be able to put themagnet on the pallet.

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You can also experiment the meissner effect here.

In certain conditions, the superconductor does not completely expel the magnetic field but lets it pass along small pillars called vortices. These vortices are positioned in front of the magnet creating a “magnetic image” of the magnet. In some cases, the vortices, once they are in place, remain pinned in their position and can no longer move.

This effect traps the magnet in front of the magnetic fingerprint created by the vortices. This effect also ties the magnet to the superconductor, even in the case of levitation. In some cases, you can even turn the superconductor upside down and you will see the magnet floating under it, still maintained by the presence of vortices. Many kinds of trains and strange hula hoops [TRAINS S’AMUSER] are made in this way.

CNRSSociété Française de PhysiqueTriangle de la physique
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CNRSSociété Française de PhysiqueTriangle de la physique