Rare earth magnets
are the rare earth element of an alloy made of a strong permanent magnet. Rare earth magnets
were developed in the 1970s and 1980s, which is the strongest type of permanent magnet ever made, the resulting magnetic field is much stronger than other types of magnets, such as ferrites or aluminum-nickel-cobalt magnets. Magnetic fields normally produced by rare earth magnets can exceed 1.4 Tesla, ferrite or ceramic magnets usually show a magnetic field of 0.5 to 1 Tesla. There are two types: neodymium magnets and samarium cobalt magne. Terfenol-d, such as magnetostrictive rare earth magnetoiron, has also been applied, in loudspeakers, for example. Rare earth magnets
are very brittle and vulnerable to corrosion, so they are usually electroplated or coated to prevent them from breaking,splintering or breaking into powder.
The development of rare earth magnets began around 1966, the discovery of yttrium and cobalt alloy YCo by KJ strnat and g. Hoffer at the materials laboratory of the U. S. Air Force at the time, they Had the largest magnetic anisotropy constant of any material known to date. The term "rare earth" may be misleading because these metals are not particularly rare or precious; they are as rich as tin or lead. However, the distribution of rare earth ores is uneven, mainly from China, which leads countries to categorize rare earth metals as of strategic importance.  Recently China's export restrictions on these materials have prompted other countries to launch research programmes to develop strong magnets that do not need them.