Magnetic properties garnets

See p. 500 of ref. 24 for a description of Ihe garnet structure which is also adopted by inany. synthetic and non-silicaie coniponnds these have been much stndied recently becan.se of their important optical and magnetic properties, e.g. ferrimagnetic vitriuni iron garnet (YIG), y> Fe (Al" b4),. 

In yttrium iron garnet Y3Fe5012 ( YIG ) a ferrimagnetic coupling (superexchange) is active between the octahedral and the tetrahedral sites. Since the tetrahedral sites are in excess, the magnetic moments do not compensate each other. The magnetic properties can be varied by substitution of yttrium by lanthanoids. 

Nearly no eddy current losses occur in electrically insulating magnetic materials. This is one of the reasons for the importance of oxidic materials, especially of spinels and garnets. Another reason is the large variability of the magnetic properties that can be achieved with spinels and garnets of different compositions. The tolerance of the spinel structure to substitution at the metal atom sites and the interplay between normal and inverse spinels allow the adaptation of the properties to given requirements. 

Silver-colored, ductile metal that is attacked slowly by air and water. The element exhibits interesting magnetic properties. Found in television tubes. Laser material such as YAG (yttrium-aluminum garnet) doped with holmium (as well as chromium and thulium) can be applied in medicine, especially in sensitive eye operations. 

Among the best-known garnets Y3Fe2Fe3012 (Y3Fe5012 yttrium-iron garnet YIG) for its magnetic properties and applications, Y3A15012 (YAG, important laser host material). 

The development of the bubble domain memory has been remarkable in that since the discovery of the growth induced anisotropy in garnets, problems connected with materials have been relatively few and not too difficult to solve. A major reason is that the different sizes and magnetic properties of the rare earths offer a wide range of choices for the materials designer. 

Magnetic properties are important in the function of electronic devices. An example is the use of yttrium iron garnet (YIG) in microwave devices. On applying an external magnetic field to a YIG disk, the input, say energy of one particular frequency selectively passes to the output. Thin films based of YIG within which magnetic waves can pass have proven to be useful. The use of lanthanides in magnetic devices as transducers is listed in Table 12.18. 

Magnetic ceramics are further classified according to their crystal structures into spinels, garnets, and hexagonal ferrites. Typical compositions and some of their magnetic properties are listed in Table 15.4. 

Similarly to spinel ferrites, garnet ferrites present a wide variety of cation substitutions, which leads to a large range of magnetic properties. 

Metselaar, R. Huyberts, M. A. H. (1973). The stoichiometry and defect structure of yttrium iron garnet and the nature of the centres active in the photomagnetic effect. Journal of Physics and Chemistry of Solids, 34,2257-63. Miyahara, S. Ohnishi, H. (1956). Cation arrangement and magnetic properties of copper ferrite-chromite series. Journal of the Physical Society, Japan, 11, 1296-7. 

Okuda, T., Katayama, T., Kobayashi, H., Kobayashi, N., Satoh, K. Yamamoto, H. (1990). Magnetic properties of Bi3Fe50,2 garnet. Journal of Applied Physics, 67, 4944-6. 

Ostorero, J., Le Gall, H., Makram, H. Escorne, M. (1985). The influence of quenching temperature on the magnetic properties of rare-earth garnet HoIG A1 single crystals. In Advances in Ceramics Fourth International Conference on Ferrites, Vol. 15. Ed. F. F. Y. Wang. American Ceramic Society, Ohio, pp. 265-73. 

The term epitaxy is used to describe the growth of a monocrystalline film of one material in a definite crystallographic orientation on a crystal face of another material, the substrate. To promote growth, there must be a correspondence of both lattices at the interface. A misfit between film and substrate results in stresses as the film grows laterally, which may affect the stability of the deposited crystal. The magnetic properties of LPE garnet films can be optimised by varying this misfit. 

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