Rare earth magnets are made from rare earth elements and are generally alloys of these elements. Since they are brittle, they are normally covered with special coating made of nickel in order to strengthen them. The result is a permanent magnet that has a very strong force in comparison to other magnets that are made from Cu/Ni/Fe or ferrite.
Samarium/Cobalt rare earth magnets do not produce as strong of a magnetic field as does the more common Neodymium variety, they are also more expensive to mine and produce. Unlike Neodymium, these Samarium/Cobalt magnets can be used in high temperature applications because they have a higher Curie Point. They are also more resistant to oxidation however, if sintered they become quite brittle and can crack easily.
The applications of rare earth magnets are extremely varied and becoming more so as the need for powerful motors and coils increases. Miniaturization is also a key to their increased use. Rare earth magnets are used in powerful motors, coils, magnetic levitation, super conductors, computers and wind turbines to just name a few.