Ferrimagnetism (redirected from Ferrimagnet)

ferrimagnetism

Type of permanent magnetism that occurs in solids, in which the magnetic fields associated with individual atoms spontaneously align themselves, some parallel (as in ferromagnetism), and others antiparallel, or paired off in opposite directions (as in antiferromagnetism). The materials are less magnetic than ferromagnets, as the antiparallel atoms dilute the magnetic effect of the parallel arrangement. Ferrimagnetism occurs mainly in magnetic oxides known as ferrites. Above a temperature called the Curie point, the spontaneous alignment is disrupted and ferrimagnetism is destroyed, but it is restored upon cooling below the Curie point.

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Ferrimagnetism

A specific type of ordering in a system of magnetic moments or the magnetic behavior resulting from such order. In some magnetic materials the magnetic ions in a crystal unit cell may differ in their magnetic properties. This is clearly so when some of the ions are of different species. It is also true for similar ions occupying crystallographically inequivalent sites. Such ions differ in their interactions with other ions, because the dominant exchange interaction is mediated by the neighboring nonmagnetic ions. They also experience different crystal electric fields, and these affect the magnetic anisotropy of the ion. A collection of all the magnetic sites in a crystal with identical behavior is referred to as a magnetic sublattice. A material is said to exhibit ferrimagnetic order when, first, all moments on a given sublattice point in a single direction and, second, the resultant moments of the sublattices lie parallel or antiparallel to one another. The notion of such an order is due to L. Néel, who showed in 1948 that its existence would explain many of the properties of the magnetic ferrites. See Ferromagnetism

In general, there is a net moment, the algebraic sum of the sublattice moments, just as for a normal ferromagnet. However, its variation with temperature rarely exhibits the very simple behavior of the normal ferromagnet. For example, in some materials, as the temperature is raised over a certain range, the magnetization may first decrease to zero and then increase again. Ferrimagnets can be expected, in their bulk properties, measured statically or at low frequencies, to resemble ferromagnets with unusual temperature characteristics. See Curie temperature