Neodymium magnet

A neodymium magnet is a magnet made out of a combination of neodymium, iron, and boron - Nd₂Fe₁₄B. These magnets are very strong in comparison to their mass, but are also mechanically fragile and have a low temperature required to lose their magnetism.

Used for stabilization in computer hard drives, Nd₂Fe₁₄B magnets are also popular with hobbyists, and a small magnet can have amazing properties - it exhibits magnetic braking when moved near a non-magnetic metal due to induced eddy current, and a somewhat larger magnet interacts strongly enough with the magnetic field of the Earth to allow its tendency to align with that field to be perceived directly when holding it. Also, a magnet significantly less than a cubic inch in size can erase a floppy disc to such an extent that the information is unrecoverable, a guarantee not present with techniques such as formatting the disc.