Electromagnetic properties of ferrites are discussed, with special regard to the garnet and spinel structures. In the compound yttrium iron garnet, Y 3Fe50i2, small amounts of tetravalent dopants, like silicon, induce charge compensating Fe2+ ions. A discussion is given of the time-dependent magneto-crystalline anisotropy caused by the presence of the Fe2+ ions. At temperatures below about 100K, a number of physical properties of silicondoped iron garnets can be changed by irradiation with infrared light. Examples are given of photoinduced changes in magnetocrystalline anisotropy, magnetic susceptibility and coercive force. Further, we discuss related photoinduced changes in the optical absorption coefficient and in linear dichroism. The effects are divided into two different classes: I) photoinduced effects which depend on the direction of the magnetization with respect to the crystallographic axes and the polarization direction of the incident light, and II) photoinduced effects that occur regardless of the prevailing magnetization distribution. In case I the effects are due to an unequal distribution of Fe2+ ions over sites which have a different orientation of their local symmetry axis with respect to the magnetization direction. In case II the photoinduced effects are due to a redistribution of Fe2+ ions over sites at different distances from the electron donating centre, e.g. the Si4+ ion. Finally magneto-optic effects in ferrites are considered. After a discussion of the phenomenological theory, the Faraday effect in the microwave and infrared region and the Faraday and Kerr effects at optical frequencies are considered.
|Title of host publication||Interaction of radiation with condensed matter : lectures presented at an international winter college, Trieste, 14 January - 26 March 1976, vol. 2|
|Place of Publication||Vienna|
|Publisher||International Atomic Energy Agency|
|Publication status||Published - 1977|