I do not think it needs to be an electro magnet just a magnet(maybe one of those new rare earth magnets).

Easy to test. Get aluminum disk, spin it, bring magnet close, if disk slows faster with magnet than without it works.

this could be a job for chojn1

would be a great replacement for drum brakes if it works

I was thinking maybe aluminum rim may substitute for a disk, or just one of the Stan's Aluminum rotors