Rare Earth Magnets are strong permanent magnets. They are made from alloys of rare earth elements. They are much stronger than alnico or ferrite magnets, and the magnetic field produced by them can exceed 1200 milliteslas.
Ceramic and ferrite magnets produce a field of 50 to 100 milliteslas, and are not as strong as rare earth magnets. Because they are very brittle, they are sometimes coated in nickel, to make them more durable and protect them from chipping and breaking, and they may be plated or coated to prevent corrosion.
Some common applications for them can include:
- Audio speakers
- Fishing reel brakes
- Bicycle dynamos
- Computer hard drives
Although these types of magnets have rare in their name, they are not particularly precious or rare, and interest in these compounds began in 1966 when it was discovered that these compounds had the largest magnetic anisotropy constant of any material then known.
Rare earth elements are metals that are ferromagnetic, which means they can be magnetized like iron, but in pure form, their magnetism only appears at low temperatures.
They have a distinct advantage over other magnets because they have a high magnetic anisotropy. They are very easy to magnetize in one particular direction and resist being magnetized in any other direction.
There are hazards associated with these magnets which are not seen with magnets of other types. Rare earth magnets larger than a couple of centimeters can be strong enough to cause injuries to body parts pinched between two magnets, or a magnet and a metal surface. The stronger magnetic fields can also be hazardous and may erase magnetic media data from devices such as credit cards and hard drives.