At the atomic level magnetism can be described through the quantum mechanical overlap of electron wave functions, when taking their quantum mechanical spin interactions into account. On the nano meter length scale it becomes more difficult to predict the behavior of a magnetic system.

When reducing the size of the magnetic material the number of domains within the material will be reduced until only a single domain is obtained. By having only single domains it is possible to produce strong permanent magnets. However if the size is reduced beyond a certain limit the sample becomes superparamagnetic and does no longer hold any ferromagnetism.

The figure illustrates the coercivity as function of magnetic particle size. As the particle shrinks fewer domains are present in the particle. At a certain size - depending in the material the magnetic particle becomes a single domain – typically in the range from 10-100nm. At sizes below 10 nm the particles becomes superparamagnetic. The spin is constantly changing within the particle.

To produce high performance permanent magnetic the crystallite size should be chosen so that the coercivity is maximized together with the remanence.

The figure illustrates the coercively as function of magnetic particle size. As the particle shrinks fewer domains are present in the particle. At a certain size - depending in the material the magnetic particle becomes a single domain – typically in the range from 10-100nm. At sizes below 10 nm the particles becomes superparamagnetic. The spin is constantly changing within the particle.

To produce high performance permanent magnetic the particle size should be chosen so that the coercivity is maximized together with the remanence.