Rare Earth Permanent Magnets, NdFeB Magnets and SmCo Magnets
Rare earth permanent magnets include SmCo magnets (Samarium-Cobalt) and NdFeB magnets (Neodymium-Iron-Boron).
SmCo magnets were developed in the 1970's and were once the most powerful permanent magnet. They have a very strong
magnetic field and tend to resist demagnetization extremely well. These magnets are also very corrosion resistant and can
operate at higher temperatures up to 300°C. They are widely used in applications in which higher operating temperature
and higher corrosion and oxidation resistance are crucial. The temperature coefficient of remanence is usually less than
NdFeB magnets are developed in the 1980's with excellent magnetic characteristics (high energy product and high
coercive force etc.) and relatively low cost. These magnets are getting to replace the traditional magnets of hard
ferrite, AlNiCo and SmCo in many fields such as electro-accoustic devices, electric motors, sensors/transducers, instruments
and meters, auto industry, petro-chemical industry and magnetic health-care products etc.
NdFeB magnets have a higher Maximum Energy Product, (BH)max, than SmCo magnets. (BH)max of NdFeB can easily reach
30 MGOe and even goes up to 48 MGOe. The temperature stability of NdFeB is not as good as SmCo magnets. Magnetic
performance of NdFeB magnets will deteriorate rapidly above 180°C. Compared to SmCo magnets, the corrosion and oxidation
resistance of NdFeB is relatively low. Therefore, A surface coating is usually applied on NdFeB magnets. Zinc or nickel
coating is common used as a protective layer.