These are permanent magnets containing rare-earth metals. The high-energy product of more than 385 kJ/m3 or 48 MGOe enables many new technical uses. Much smaller magnet systems or considerably higher magnetic energies for the same size in comparison to conventional magnetic materials such as barium ferrites or AINiCo have become possible. As a comparison: With the same energy content, a barium ferrite magnet has to have a volume 6 times larger. To create a field with the strength of 100 mT (1,000 G) at a 1 mm distance from the pole, a barium ferrite magnet must be around 25 times larger than a samarium-cobalt magnet.
The energy product of the new neodymium-iron-boron magnets is about a further 70% higher than that of the samariumcobalt magnets mentioned in the example.
The following is a comparison of the energy products (B x H) max. of several magnet materials
|Plastic bonded barium ferrite, anisotropic (Betaflex)||12 kJ/m3|
|Hard ferrite, sintered, anisotropic (SrFe)||32 kJ/m3|
|AlNiCo 500||40 kJ/m3|
|Plastic bonded SmCo, AlphaMagnet||64 kJ/m3|
|Plastic bonded NdFeB, NeoAlphaMagnet||96 kJ/m3|
|Samarium-Cobalt, DeltaMagnet (SmCo)||225 kJ/m3|
|Neodymium-Iron-Boron, NeoDeltaMagnet (NdFeB)||360 kJ/m3|
What are "rare-earth metals"?Rare-earth metals, also called Lanthanides , are 15 elements, numbered between 57 and 71 in the periodic table. They make up about 1/7 of all elements occurring naturally. This means the rare-earth elements are not rare at all. Of economic importance, for example, are: Cerium (Ce) for glass manufacturing or steel production; Lanthanium (La) for X-ray film manufacturing and also for making catalytic converters for reducing exhaust emissions; Europium (Eu) for making the red colour in TV screens visible; Samarium (Sm) and Neodymium (Nd) for the manufacture of magnet materials with the highest energy product.
Samarium forms only a fraction of the rare-earth elements.Production with a high ratio of purity is costly. Neodymium forms a higher percentage of the rare-earth elements.
The costly processing to make the finished magnet means that rare-earth magnets are more expensive in comparison to conventional permanent magnet materials. Samarium-Cobalt magnets also contain the expensive material Cobalt (Co).
Large-volume usage is limited due to the high costs.
How are high-energy magnets produced?
Normally both SmCo and NdFeB magnets are alloyed by melting. Afterwards the material ingots are crushed and milled into fine powders, compressed under the influence of a magnetic field and finally sintered.
We process ingots made by isostatic pressing and then sintering in large dimensions. These ingots are then cut up using diamond saws under water. Discs and rings are also produced with diamond tools. To produce high volume parts the powder is compressed into shapes and then sintered. Only simple geometric shapes can be produced.
After the magnet has its final shape it must be magnetised until saturation is occurs. This requires a very high magnetic fields. To produce this strong magnetic fields, charged capacitor batteries are discharged in an air-core coil. The magnet body situated in the inner hole of the low-impedance air-core coil is magnetised until saturation by the induced strong magnetic field when the impulse discharge is "fired off". Magnetisation is only possible parallel to the magnetic orientation in which it was "impregnated" during production!
We supply standard magnets magnetised to saturation. On request, we also supply magnets unmagnetised and carry out a later magnetisation in the system.
SmCo magnets are very hard and brittle. NdFeB magnets are hard and less brittle.
The magnets oxidise in a humid atmosphere; SmCo only very slightly, but NdFeB to a greater extent. SmCo magnets are relatively resistant to water. NdFeB magnets oxidise to a very high degree and dissolve slowly in water.
NdFeB magnets are protected against corrosion by electroplating with tin or nickel-plating.
Structural losses occur with exposure to radiation. As a result the magnetic properties are altered negatively.