Degausser
A device that uses a strong alternating magnetic field to reset a whole medium's magnetisation at once — bulk-erasing tapes and disks.
The name comes from the gauss, the unit of magnetic flux density. A degausser exposes the medium to a field far above its coercivity that then decays toward zero, leaving the magnetic domains in random, net-zero orientation. Classic types are decaying-AC coils and rotating permanent magnets. NIST SP 800-88 lists degaussing as a valid sanitisation method for magnetic media.
Two catches: on a modern hard drive it also erases the factory-written servo tracks, so the drive is dead afterwards — degaussing is destructive, not recycling. And on flash and SSDs it does nothing at all, because there is no magnetism to disturb. It will also happily clean up a CRT's colour purity, which is an entirely different use.