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Types of Rare Earth Magnets
Two types of rare earth magnets exist: samarium-cobalt magnets and neodymium magnets. Samarium-cobalt magnets exhibit a weaker magnetic field than neodymium magnets and cost considerably more. Their Curie temperature, or the temperature at which they lose their magnetism, is also higher. Samarium-Cobalt are considerably more brittle than neodymium magnets, yet they have a higher resistance to oxidization. In contrast, neodymium magnets exhibit a much stronger magnetic field and are more affordable. Made of an alloy of neodymium, iron and boron, these magnets have a much lower Curie temperature as well as a lower resistance to oxidization.
History
Samarium-Cobalt magnets were invented by Dr. Karl J. Strnat at the U.S. Air Force Materials Laboratory at Wright-Patterson Air Force Base in 1966. He further advanced his formula in 1972; though, these magnets found little use due to their high cost. Neodymium magnets were discovered by the General Motors Corporation in conjunction with Sumitomo Special Metals in 1982. They combined neodymium, iron and boron to create a new, stronger magnet in an effort to do away with the high cost of the permanent magnets at the time. They also discovered that the magnets were highly corrosive, thus leading to the nickel and copper-plated coating still in use.
Applications
Though relatively expensive, Samarium-Cobalt magnets are extremely resistant to demagnetization and are able to be used at more extreme temperatures. They are currently used in guitar pickups, racecar motors and turbomachines such as windmills, centrifugal pumps and propellers. Neodymium magnets are far less expensive and thus, have a wider range of application. These magnets have been used in computer hard disk drives, cordless tools, speakers and headphones, and in drive motors for a number of automobiles. Companies such as Magcraft have even used these magnets to keep roller coasters on their tracks as well as to slow elevators.
Hazards
Due to the powerful nature of their magnetic field in particular, rare earth magnets exhibit unique hazards. Given the fragile nature of Samarium-Cobalt magnets, the greatest hazard when dealing with them is their propensity to break and chip, causing shards of flying debris. Strong magnetic fields can also erase data from hard disks and credit cards. Since neodymium magnets can be made relatively cheaper and thus, smaller, they present a hazard to children. These magnets can be swallowed, subsequently bonding together in the digestive track, according to the Consumer Product Safety Commission. Given that these magnets are the most powerful, they can pinch skin and even crush bone when bonding together, or to a metal surface.