Remanence or remanent magnetization or residual magnetism is the magnetization left behind in a ferromagnetic material (such as iron) after an external magnetic field is removed. Colloquially, when a magnet is "magnetized", it has remanence. The remanence of magnetic materials provides the magnetic memory in magnetic storage devices, and is used as a source of information on the past Earth's magnetic field in paleomagnetism. The word remanence is derived from remanent, meaning "that which remains".

The equivalent term residual magnetization is generally used in engineering applications. In transformers, electric motors and generators a large residual magnetization is not desirable (see also electrical steel) as it is an unwanted contamination, for example, a magnetization remaining in an electromagnet after the current in the coil is turned off. Where it is unwanted, it can be removed by degaussing.

Sometimes the term retentivity is used for remanence measured in units of magnetic flux density.

Types

Saturation remanence

thumb|Fig. 1 A family of AC [[hysteresis loops for grain-oriented electrical steel (B<sub>r</sub> denotes remanence and H<sub>c</sub> is the coercivity).]]

The default definition of magnetic remanence is the magnetization remaining in zero field after a large magnetic field is applied (enough to achieve saturation). It is called the initial remanence or the isothermal remanent magnetization (IRM).

Another kind of IRM can be obtained by first giving the magnet a saturation remanence in one direction and then applying and removing a magnetic field in the opposite direction. Yet another kind of remanence can be obtained by demagnetizing the saturation remanence in an ac field. This is called AC demagnetization remanence or alternating field demagnetization remanence and is denoted by symbols like M<sub>af</sub>(H).

If the particles are noninteracting single-domain particles with uniaxial anisotropy, there are simple linear relations between the remanences. and is assumed in some models to represent the lowest-energy state for a given field. There are several ways for experimental measurement of the anhysteretic magnetization curve, based on fluxmeters and DC biased demagnetization. ARM has also been studied because of its similarity to the write process in some magnetic recording technology and to the acquisition of natural remanent magnetization in rocks.

Examples

{| class="wikitable sortable"

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! Material !! Remanence !! References

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| Ferrite (magnet) || ||

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| Samarium-cobalt magnet || ||

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| AlNiCo 5 || ||

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| Neodymium magnet || ||

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See also

  • Coercivity
  • Hysteresis
  • Rock magnetism
  • Thermoremanent magnetization
  • Viscous remanent magnetization

Notes

References

  • Coercivity and Remanence in Permanent Magnets
  • Magnet Man

ja:残留磁束密度