Magnetic flux pinning sometimes there and sometimes not.

[2sin54]

Hello. As far as I know about superconductors, if you put a superconducting material in a magnetic field and then cool that material below its critical temperature, the material should lock to that magnetic field (magnetic flux pinning). Now I have seen videos where the locked magnet/material is pushed away but it bounces back to its locked state (like here ).

Now there is another video where the material gets pushed away and re-locks in a different position (). My question is, why in the latter video the superconducting disc did not stay in its original position and allowed itself to be locked in a new one numerous times? I apologize for the mistakes I made in terminology and English.

 

[f95toli]

The flux pinning occurs along defects, impurties etc. where the flux "sticks"; if you apply enough force you can move the flux (i.e. the vortices) around and then it will stick in a new configuration.
It is also possible to have multiple stable configurations.

Am "ideal" type II superconductor made from a perfect crystal would behave differently.

 

[2sin54]

Thank you.