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:''Not to be confused with ferromagnetism; for an overview see magnetism'' In physics, a ferrimagnetic material is one that has populations of atoms with opposing magnetic moments, as in antiferromagnetism; however, in ferrimagnetic materials, the opposing moments are unequal and a spontaneous magnetization remains. This happens when the populations consist of different materials or ions (such as Fe2+ and Fe3+). Ferrimagnetism is exhibited by ferrites and magnetic garnets. The oldest known magnetic substance, magnetite (iron(II,III) oxide; Fe3O4), is a ferrimagnet; it was originally classified as a ferromagnet before Néel's discovery of ferrimagnetism and antiferromagnetism in 1948.〔L. Néel, ''Propriétées magnétiques des ferrites; Férrimagnétisme et antiferromagnétisme'', Annales de Physique (Paris) 3, 137-198 (1948).〕 Some ferrimagnetic materials are YIG (yttrium iron garnet), cubic ferrites composed of iron oxides and other elements such as aluminum, cobalt, nickel, manganese and zinc, hexagonal ferrites such as PbFe12O19 and BaFe12O19, and pyrrhotite, Fe1-xS.〔Klein, C. and Dutrow, B., Mineral Science, 23rd ed., Wiley, p. 243〕 ==Effects of temperature== Ferrimagnetic materials are like ferromagnets in that they hold a spontaneous magnetization below the Curie temperature, and show no magnetic order (are paramagnetic) above this temperature. However, there is sometimes a temperature ''below'' the Curie temperature at which the two opposing moments are equal, resulting in a net magnetic moment of zero; this is called the '' magnetization compensation point''. This compensation point is observed easily in garnets and rare earth-transition metal alloys (RE-TM). Furthermore, ferrimagnets may also have an ''angular momentum compensation point'' at which the net angular momentum vanishes. This compensation point is a crucial point for achieving high speed magnetization reversal in magnetic memory devices.〔C. D. Stanciu, A. V. Kimel, F. Hansteen, A. Tsukamoto, A. Itoh, A. Kirilyuk, and Th. Rasing, ''Ultrafast spin dynamics across compensation points in ferrimagnetic GdFeCo: The role of angular momentum compensation'', Phys. Rev. B 73, 220402(R) (2006).〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ferrimagnetism」の詳細全文を読む スポンサード リンク
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