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This is an audio version of the Wikipedia Article:
https://en.wikipedia.org/wiki/Rare-earth_magnet


00:01:43 1 Explanation of strength
00:04:12 2 Magnetic properties
00:05:08 3 Types
00:05:17 3.1 Samarium-cobalt
00:06:02 3.2 Neodymium
00:07:31 4 Hazards
00:08:33 5 Applications
00:09:02 5.1 Common applications
00:10:17 5.2 Other applications
00:11:28 6 Rare-earth-free permanent magnets
00:12:10 7 See also



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SUMMARY
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Rare-earth magnets are strong permanent magnets made from alloys of rare-earth elements. Developed in the 1970s and 1980s, rare-earth magnets are the strongest type of permanent magnets made, producing significantly stronger magnetic fields than other types such as ferrite or alnico magnets. The magnetic field typically produced by rare-earth magnets can exceed 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, chipping, or crumbling into powder.
The development of rare-earth magnets began around 1966, when K. J. Strnat and G. Hoffer of the US Air Force Materials Laboratory discovered that an alloy of yttrium and cobalt, YCo5, had by far the largest magnetic anisotropy constant of any material then known.The term "rare earth" can be misleading, as some of these metals can be as abundant in the Earth's crust as tin or lead, but rare earth ores are unevenly distributed, not existing in seams like coal or copper, so in any given cubic kilometre of crust they are "rare". The major source is currently China. Some countries classify rare earth metals as strategically important, and recent Chinese export restrictions on these materials have led some to initiate research programs to develop strong magnets that do not require rare earth metals.