The magnet creates a field that changes the polarity of a tiny, tiny portion of the metal particles which coat each platter's surface.

In motor racing, for instance, if a driver is taken to hospital after a crash the metal in the capsule would prevent the use of an MRI scanner, which is essentially a powerful magnet.

If you do have a really good magnet collection, buy a metal board, arrange the magnets artistically and display them somewhere else in your home.