3 Neodymium Disc Magnets 6 10 20 mm dia.mm002566
WARNING: NOT SUITABLE FOR YOUNG CHILDREN.
These are very powerful magnets, and should be handled carefully, and kept away from pacemakers, televisions, credit cards etc.
Neodymium is a 'rare earth' magnetic material and has the greatest pulling force of all permanent magnets. Rare-earth magnets are strong permanent magnets made from alloys of rare earth elements. Developed in the 1970s and '80s, rare-earth magnets are the strongest type of permanent magnets made, producing significantly stronger magnetic fields than other types such as ferrite or alnico magnets. The magnetic field typically produced by rare-earth magnets can be in excess of 1.4 teslas, whereas ferrite or ceramic magnets typically exhibit fields of 0.5 to 1 tesla. There are two types: neodymium magnets and samarium-cobalt magnets. Rare earth magnets are extremely brittle and also vulnerable to corrosion, so they are usually plated or coated to protect them from breaking, chipping, or crumbling into powder. The term "rare earth" can be misleading as these metals are not particularly rare or precious; they are about as abundant as tin or lead. The development of rare earth magnets began around 1966, when K. J. Strnat and G. Hoffer of the US Air Force Materials Laboratory discovered that an alloy of yttrium and cobalt, YCo5, had by far the largest magnetic anisotropy constant of any material then known.