Originally posted by KazetNagorra
Are you talking about permanent magnets (in that case, I don't know)? In practise, the strongest magnets are often made using superconductors, because these don't generate any heat (no resistance) so you can pump huge currents through them to create strong magnets.
I am partly talking about permanent magnets but I would also be interested in non-permanent non-metallic magnets as the would still be very useful as electromagnets in electric motors and electric generators.
The non-metallic magnets I am talking about here are specifically the ones that work at room temperature so that rules out superconductor ones (at least for now).
There have recently been invented plastic and polymer based magnets that work at room temperature but I have been completely unable to find any details of the strength of their magnetism as compared with conventional metallic magnets and it is this that I want to know about.