As far as I can tell, a chunk of superconductor which is topologically a ball, cannot produce a permanent magnetic field. (This should be clear due to the "Meissner effect.") A chunk which is topologically a solid torus, can (CERN magnets). So for example, if the Earth's interior were superconducting as opposed to normal-conducting, then I presume the Earth would have no magnetic field. Now perhaps there might be some way out of this logic trap for those who believe the neutron stars have superconducting interiors (?).... but at least naively, the fact neutron stars have enormous magnetic fields, seems to contradict the super-theory. "Magnetars" have fields up to 10^11 Tesla, Pulsars 10^8. It seems to me, the onus is on the proponents of the super-theory to explain how to escape this trap. And if you look in the papers I cited which claim "the first direct evidence for superconducting neutron stars" you will see not the teeniest tiniest mention of this massive contradiction albeit it does contain this interesting footnote: "There is, to date, no evidence for the presence of a magnetic field in the Cassiopeia A neutron star." But most neutron stars which have been detected are pulsars and hence have huge fields. Incidentally, the "pressure" associated with a magnetic field B is B*B/(2*mu0) which for B=10^11 tesla is pressure=6*10^27 pascals=6*10^22 atmospheres. Sustained. The pressure inside an H-bomb explosion is a mere 10^15 pascals.