A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet. A noticeable force on other materials without actually contacting them. This force is known as a magnetic force and may either attract or repel. While all known materials exert some sort of magnetic force, it is so small in most materials that it is not readily noticeable. With other materials, the magnetic force is much larger, and these are referred to as magnets. The Earth itself is a huge magnet.
A "soft" or "impermanent" magnet is one which loses its memory of previous magnetizations. "Soft" magnetic materials are often used in electromagnets to enhance (often hundreds or thousands of times) the magnetic field of a wire that carries an electrical current and is wrapped around the magnet; the field of the "soft" magnet increases with the current.A "hard" or "permanent" magnet is one which stays magnetized for a long time, such as magnets often used in refrigerator doors.
Permanent magnets attribute to hard magnets.They occur naturally in some rocks, particularly lodestone, a hard, crystalline iron ferrite mineral that derives its magnetism from the effect the earth's magnetic field has on it, but Various steel alloys can also be magnetized, are now more commonly manufactured. In our present technology, Permanent magnet applications include compasses, electric motors, microwave ovens, coin-operated vending machines, light meters for photography, automobile horns, televisions, loudspeakers, and tape recorders.
Rare earth magnets are important materials in manufacturing. Rare-earth magnets are strong, permanent magnets made from alloys of rare earth elements, which have a partially occupied electron shell (which can accommodate up to 14 electrons.) The spin of these electrons can be aligned, resulting in very strong magnetic fields, and therefore these elements are used in compact high-strength magnets where their higher price is not a concern. Rare-earth magnets are substantially stronger than ferrite or alnico magnets.Therefor Rare earth magnets are also called strong magnets sometimes. The magnetic field typically produced by rare-earth magnets can be in excess of 1.2 teslas. Ferrite or ceramic magnets typically exhibit fields of 50 to 100 milliteslas. Because rare earth magnets are extremely brittle, they are usually nickel-coated to protect them from breaking and chipping, hence their typically shiny, corrosion resistant nature.
Rare earth magnet is not rare or precious. It Common applications include:Computer hard drives, Audi speakers ,Bicycle dynamos,Fishing Reel brakes. Other applications of rare-earth magnets include: stop motion animation as tie-downs when the use of traditional screw and nut tie-downs is impractical; Diamagnetic levitation experimentation, the study of magnetic field dynamics and superconductor levitation.;Launched roller coaster technology found on roller coaster and other thrill rides.
References
http://www.answers.com/topic/magnet#Dictionary
http://en.wikipedia.org/wiki/Magnet#Types_of_permanent_magnets