Does anyone know of a substance that can block a magnetic field?
Look up something called "mu metals".
Caution: there are no practical material (of arbitrary thickness) that can shield magnetic field of arbitrary strength. So your question is rather vague.
I've heard of one, I think it started with an I.
golansha, are you talking about the meissner effect ?
Check the superconductors.
(Not blocking but an interesting effect!)
Are you talking about superconductors, Gokul?
I've found such an interesting question on this website,
It is also very helpful for my little knowledge about the magnetic field. So thanks for the question
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