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Rare-earth magnet
From Wikipedia, the free encyclopedia
Ferrofluid on glass, with a rare-earth magnet underneath.

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 and have significant performance advantages over ferrite or alnico magnets. The magnetic field typically produced by rare-earth magnets can be in excess of 1.4 teslas, whereas ferrite or ceramic magnets typically exhibit fields of 0.5 to 1 tesla. There are two types: neodymium magnets and samarium-cobalt magnets. Rare earth magnets are extremely brittle and also vulnerable to corrosion, so they are usually plated or coated to protect them from breaking and chipping.

The term "rare earth" can be misleading as these metals are not particularly rare or precious;[1][2] they are about as abundant as tin or lead.[3] Interest in rare earth compounds as permanent magnets began in 1966, when K. J. Strnat and G. Hoffer of the US Air Force Materials Laboratory discovered that [[YCo5]] had by far the largest magnetic anisotropy constant of any material then known.[4]