Neodymium magnet

http://en.wikipedia.org/wiki/Neodymium_magnet

A neodymium magnet (also known as NdFeB, NIB or Neo magnet), the most widely used type of rare-earth magnet, is a permanent magnet made from an alloy of neodymium, iron and boron to form the Nd₂Fe₁₄B tetragonal crystalline structure.

Developed in 1982 byGeneral Motors and Sumitomo Special Metals, neodymium magnets are the strongest type of permanent magnet commercially available.They have replaced other types of magnet in the many applications in modern products that require strong permanent magnets, such as motors in cordless tools, hard disk drives and magnetic fasteners.

Description

The tetragonal Nd₂Fe₁₄B crystal structure has exceptionally high uniaxial magnetocrystalline anisotropy (HA~7 teslas - magnetic field strength H in A/m versus magnetic moment in A.m²).^[4] This gives the compound the potential to have high coercivity (i.e., resistance to being demagnetized). The compound also has a high saturation magnetization (J_s ~1.6 T or 16 kG) and typically 1.3 teslas. Therefore, as the maximum energy density is proportional to J_s², this magnetic phase has the potential for storing large amounts of magnetic energy (BH_max ~ 512 kJ/m³ or 64 MG·Oe). This property is considerably higher in NdFeB alloys than in samarium cobalt (SmCo) magnets, which were the first type of rare-earth magnet to be commercialized. In practice, the magnetic properties of neodymium magnets depend on the alloy composition, microstructure, and manufacturing technique employed.

History

In 1982, General Motors (GM) and Sumitomo Special Metals discovered the Nd₂Fe₁₄B compound. The research was initially driven by the high raw materials cost of SmCopermanent magnets, which had been developed earlier. GM focused on the development of melt-spun nanocrystalline Nd₂Fe₁₄B magnets, while Sumitomo developed full-densitysintered Nd₂Fe₁₄B magnets.

GM commercialized its inventions of isotropic Neo powder, bonded Neo magnets, and the related production processes by founding Magnequench in 1986 (Magnequench has since become part of Neo Materials Technology, Inc., which later merged into Molycorp). The company supplied melt-spun Nd₂Fe₁₄B powder to bonded magnet manufacturers.

The Sumitomo facility became part of the Hitachi Corporation, and currently manufactures and licenses other companies to produce sintered Nd₂Fe₁₄B magnets. Hitachi holds more than 600 patents covering neodymium magnets.

Chinese manufacturers have become a dominant force in neodymium magnet production, based on their control of much of the world's sources of rare earth ores.

The United States Department of Energy has identified a need to find substitutes for rare earth metals in permanent magnet technology, and has begun funding such research. TheAdvanced Research Projects Agency has sponsored a Rare Earth Alternatives in Critical Technologies (REACT) program, to develop alternative materials. In 2011, ARPA-E awarded 31.6 million dollars to fund Rare-Earth Substitute projects.