All About Neodymium Magnets
Overview of the operating properties of NIB magnets.
Neodymium magnets (also known as rare earth, Neo, NIB or NdFeB magnets) were invented in 1982 and are the strongest type of magnets.
There are two basic ways that NIB magnets are made: sintered and bonded.
Sintered NIB Magnets
Sintered NIB magnets have the highest strength but are limited to relatively simple geometries and can be brittle. They are made by pressure forming the raw materials into blocks, which then go through a complex heating process. The block is then cut to shape and coated to prevent corrosion. Sintered magnets are typically anisotropic, which means they have a preference for the direction of their magnetic field. Magnetizing a magnet against the “grain” will reduce the strength of the magnet by up to 50%. Commercially available magnets are always magnetized in the preferred direction of magnetization.
Bonded NIB Magnets
Bonded NIB magnets are typically about half as strong as sintered magnets but are less expensive and can be made into almost any size and shape. Raw materials are mixed with epoxy as a binder, pressed into a die cavity and heat cured. Bonded magnets are isotropic, which means they don’t have a “grain” or a natural preference for the direction of their magnetic field.
NIB magnets really are permanent magnets, as they lose their magnetism, or degauss naturally, at approximately 1% per century. They generally operate within the temperature range of -215°F to 176°F (-138°C to 80°C). For applications that require a broader temperature range, Samarium Cobalt (SmCo) magnets are used.
Because uncoated sintered NIB will corrode and crumble with exposure to the atmosphere, they are sold with a protective coating. The most common coating is made of nickel, though other commercially available coatings provide resistance to high temperature, high humidity, salt spray, solvents and gases.
NIB magnets come in different grades, which correspond to the strength of their magnetic fields, ranging from N35 (weakest and least expensive) to N52 (strongest, most expensive and more brittle). An N52 magnet is approximately 50% stronger than an N35 magnet (52/35 = 1.49). In the US, it is typical to find consumer grade magnets in the N40 to N42 range. In volume production, N35 is often used if size and weight are not a major consideration as it is less expensive. If size and weight are critical factors, higher grades are typically used. There is a premium on the price of the highest grade magnets so it is more common to see N48 and N50 magnets used in production versus N52.