Editing Remanence (section)

=== Isothermal remanence ===
Often a single measure of remanence does not provide adequate information on a magnet. For example, magnetic tapes contain a large number of small magnetic particles (see [[magnetic storage]]), and these particles are not identical.  Magnetic minerals in rocks may have a wide range of magnetic properties (see [[rock magnetism]]). One way to look inside these materials is to add or subtract small increments of remanence. One way of doing this is first [[Magnet#Magnetization and demagnetization|demagnetizing]] the magnet in an AC field, and then applying a field '''''H''''' and removing it.  This remanence, denoted by '''''M'''''<sub>r</sub>('''''H'''''), depends on the field.<ref name=Wohlfarth>{{Harvnb|Wohlfarth|1958}}</ref> It is called the ''initial remanence''<ref>{{Harvnb|McCurrie|Gaunt|1966}}</ref> or the ''isothermal remanent magnetization (IRM)''.<ref name="Néel">{{Harvnb|Néel|1955}}</ref>

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.<ref name=Wohlfarth/>  This is called ''demagnetization remanence'' or ''DC demagnetization remanence'' and is denoted by symbols like '''''M'''''<sub>d</sub>('''''H'''''), where '''''H''''' is the ''magnitude'' of the field.<ref name=Pfeiffer>{{Harvnb|Pfeiffer|1990}}</ref>  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.<ref name=Wohlfarth/>