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The existence of magnetic domains in the material

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A good permanent magnet should produce a high magnetic field with a low mass, and should be stable against the influences which would demagnetize it. The desirable properties of such magnets are typically stated in terms of the remanence and coercivity of the magnet materials. 

When a ferromagnetic material is magnetized in one direction, it will not relax back to zero magnetization when the imposed magnetizing field is removed. The amount of magnetization it retains at zero driving field is called its remanence. It must be driven back to zero by a field in the opposite direction; the amount of reverse driving field required to demagnetize it is called its coercivity. If an alternating magnetic field is applied to the material, its magnetization will trace out a loop called a hysteresis loop. The lack of retraceability of the magnetization curve is the property called hysteresis and it is related to the existence of magnetic domains in the material. Once the magnetic domains are reoriented, it takes some energy to turn them back again. This property of ferrromagnetic materials is useful as a magnetic "memory". Some compositions of ferromagnetic materials will retain an imposed magnetization indefinitely and are useful as "permanent magnets".

The table below contains some data about materials used as permanent magnets. Both the coercivity and remanence are quoted in Tesla, the basic unit for magnetic field B. The hysteresis loop above is plotted in the form of magnetization M as a function of driving magnetic field strength H. This practice is commonly followed because it shows the external driving influence (H) on the horizontal axis and the response of the material (M) on the vertical axis. Besides coercivity and remanence, a quality factor for permanent magnets is the quantity (BB0/?0)max. A high value for this quantity implies that the required magnetic flux can be obtained with a smaller volume of the material, making the device lighter and more compact.





Broad prospects for application of NdFeB magnets

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Rare earth functional materials will become the focus of development of rare earth functional materials with other materials can not match the optical electromagnetic properties, are widely used in electronics, new energy, environmental protection and other emerging areas, commonly used rare earth materials, rare earth luminescent materials, polishing materials, magnetic materials,hydrogen storage materials. Rare earth functional materials because of its special properties, or will become the focus of the development of new materials industry. With the rapid development of energy-efficient lighting and consumer electronics industries, rare earth luminescent materials application demands explosive growth.

With the countries officially released out of incandescent roadmap incandescent production capacity in China in 2013 dropped to 1.42 billion, the energy-saving lamps production will reach 6 billion, for the production of energy-saving lamps. Rare earth luminescent materials as the production of energy-saving lamps must be on the basis of raw materials, the market demand is bound to usher in the explosive growth. Is expected to 2013, China's energy-saving lamps with rare earth luminescent materials market size will reach 8,000 to 10,000 tons, the annual compound growth rate of 21%. Rare earth permanent magnet materials as the field of application of the most widely used permanent magnet materials, accounting for 60% of the total consumption of rare earth new materials. The third generation of permanent magnet materials, NdFeB magnetic permanent magnet in the world is now, but also the largest consumer of rare earth rare earth new materials.

High-performance NdFeB permanent magnet materials applications include: new energy and energy saving and environmental protection fields, including wind power, energy-saving elevator, energy saving air conditioning, new energy vehicles and traditional applications (VCM and consumer electronics). Hybrid cars and energy-saving and environmental protection air conditioning demand in the future, energy saving and new energy field will be the main application areas of high performance NdFeB permanent magnet materials. Hybrid cars, for example, the average of each hybrid cars need to 5kg high-performance NdFeB permanent magnet materials, Click here to estimate that by 2014, China's hybrid automobile industry demand will reach 7800 tons of high-performance NdFeB .






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