Rare-earth magnet

Rare-earth magnets are strong permanent magnets made from alloys of rare earth elements.
Developed in the 1970s and '80s, rare-earth magnets are the strongest type of permanent magnets made. They have much stronger magnetic fields than other types such as ferrite or alnico magnets.
There are two types: neodymium magnets and samarium-cobalt magnets. Some rare-earth magnets such as Terfenol-D are magnetostrictive. They also have uses e.g. in speakers.
Rare earth magnets are extremely brittle and also vulnerable to corrosion, so they are usually plated or coated to protect them from breaking, chipping, or crumbling into powder.