Magnetic Materials

First created: Mon May 28 2001
Last updated: Mon May 28 2001
The magnets used in the probe are of ceramic type. More exotic magnets are available that have better temperature stabilty.

Magnet Physical Data

Ceramic (Ferrite) Magnet is manufactured from oxide materials using powder metallurgical process. Ceramic magnet is most widely used because of its low cost, high-energy, good electric insulation and excellent resistance to demagnetization. The most common type of ceramic magnets are anisotropic strontium, anistropic barium and isotropic barium magnet.

SmCo (Samarium Cobalt) Magnet is one of kind of rare earth maget with a high percentage of samarium, whitch is relatively stable against temperature change. With high energy product and excellent coercove force, this material is ideally compact and suitable to highly efficient machines and components, and widely used in application in which higher operation temperature, higher corrosion and oxidation resistance are crecial. Two common compositions of this kind of magnet are Sm1Co5 and Sm2Co17.

AlNiCo (Aluminum-Nickle-Cobalt) Magnet is high-energy permanent magnet, which posses high flux density, high coercive, high energy product and extreme stability for temperature changes. It exhibits good resistance to demagnetization, stability in high temperatures and excellent conduction.

reference: descriptions from magtek

Material Br Hc BHmax Tcoef of Br Tmax Tcurie
NdFeB 12,800 12,300 40 -0.12 150 310
SmCo 10,500 9,200 26 -0.04 300 750
Alnico 12,500 640 5.5 -0.02 540 860
Ceramic or Ferrite 3,900 3,200 3.5 -0.20 300 460

Br is the measure of its residual magnetic flux density in Gauss, which is the maximum flux the magnet is able to produce. ( 1Gauss is like 6.45 lines/sq in)
Hc is the measure of the coercive magnetic field strength in Oersted, or the point at which the magnet becomes demagnetized by an external field. ( 1Oersted is like 2.02 ampere-turns/inch) BHmax is a term of overall energy density. The higher the number, the more powerful the magnet.
Tcoef of Br is the temperature coefficient of Br in terms of % per degree Centigrade. This tells you how the magnetic flux changes with respect to temperature. -0.20 means that if the temperature increases by 100 degrees Centigrade, its magnetic flux will decrease by 20%!
Tmax is the maximum temperature the magnet should be operated at. After the temperature drops below this value, it will still behave as it did before it reached that temperature (it is recoverable).
Tcurie is the Curie temperature at which the magnet will become demagnetized. After the temperature drops below this value, it will not behave as it did before it reached that temperature. If the magnet is heated between Tmax and Tcurie, it will recover somewhat, but not fully (it is not recoverable).

reference: data from cited in rhoadley

BTW, the "Tcoef of Br" numbers are for C and should be multiplied by .55 (5/9) when using F.