Rare-earth magnets can be divided into two distinctive groups: Sm-Co magnets and Nd-Fe-B magnets. The Sm-Co magnets are known for its powerful magnetic force. Their resistance to heat and rust are much valued properties, but lacks in mechanical strength. Along with Nd-Fe-B magnets, demands are high for these magnets because they are considered suitable materials as the market pursues for smaller and lighter products. Nd-Fe-B magnets can produce the strongest magnetic field among products currently available on the global market. They can be processed into any shape ? round, square, or ring type, etc- according to the purpose of use. The magnets have high mechanical strength, but are not so resistant to rust, so the surface of these magnets have been specially coated and they must be used in an environment of under 80 degrees Celsius.