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The strongest permanent magnets in the world are neodymium (Nd) magnets, they are made from magnetic material made from an alloy of neodymium, iron and boron to form the Nd2Fe14B structure. Neodymium magnets are considered part of the family of rare earth magnets because their main element is the rare earth element, neodymium. Despite the name, rare earth elements are relatively abundant in the Earth’s crust, however, they are rarely found in their concentrated form, and rather they are typically dispersed with other elements.
Samarium cobalt is the other type of rare earth magnet; samarium cobalt (SmCo) magnets were developed before neodymium magnets and while not as strong as neodymium magnets they have a greater resistance to corrosion and can operate and maintain their performance at higher temperatures. To increase the performance of both neodymium and samarium cobalt magnets traces of additional rare earth elements such as dysprosium (Dy) and praseodymium (Pr) are added.
Rare earth elements in the periodic table highlighted in red
The neodymium compound, Nd2Fe14B was first discovered in 1982 by General Motors and Sumitomo Special Metals. Since they were first introduced, stronger grades of neodymium magnets have become commercially available as manufacturing techniques have become more advanced. The strongest grade currently available is the N55, although it is not yet widely used. More common are N42 and N52 grades; a 50mm x 50mm x 25mm N52 neodymium block is capable of supporting a steel weight of 116kg vertically when in flush contact with a mild steel surface of equal thickness and produces a Gauss rating, the unit measurement of flux density, of 5,500 over 7,800 times stronger than that produced by the Earth at its magnetic poles. Electromagnets which harness electric currents to produce magnetic fields can be many times stronger than permanent magnets, however, they need a significant electrical current to produce their magnetic field.
Neodymium magnets are so strong because of their high resistance to demagnetisation (coercivity) and their high levels of magnetic saturation allowing them to generate large magnetic fields. A magnet's strength is represented by its maximum energy product value (BHmax) which is measured in Mega Gauss Oersteds (MGOe). Maximum energy product is a product of remanence (Br) and coercivity (Hc) and represents the area under the graph of the second quadrant hysteresis loop.
Example hysteresis loop
Typical Maximum Energy Product values of neodymium magnets
Because of their strength, even tiny neodymium magnets can be effective. This also makes them incredibly versatile; as we all go about our modern lives we are never far from a neodymium magnet, you are likely to have one in your pocket right now, or if you are reading this article on a smartphone, you might even have one in your hand!