Ferrites-garnets

Garnet-structure ferrites. Garnet, ideally A3 B2[T04]3, is isometrie (Ia3d) with a straeture built of TO4 tetrahedra and BOe oetahedra linked by shared vertiees that form AOg dodeeahedra. The A-sites aeeommodate divalent (Ca, Mn, Fe) and trivalent (Y, REE) elements. The B-site may contain various di-, tri- (Fe, Al, Ga, Cr, Mn, In, Sc, Co), tetra- (Zr, Ti, Sn, Ru) and even pentavalent elements (Nb, Ta, Sb). The T-sites are filled with tetravalent (Si, Ge, Sn) but may be also occupied by trivalent (Al, Ga, Fe) and pentavalent (P, V, As) elements. Synthetic garnets form multicomponent solid solutions that provide opportunities for incorporating of HEW elements into the structure [149]. 

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

The dark-held method was hrst applied to study magnetic media in reference 73, where the domain structure was visualized in ferrite-garnet hlms. A signihcant contribuhon to the development of MO dark-held microscopy was made by Thiaville and co-workers [74,75], who ophcally detected the vertical Bloch lines (VBLs) in iron-garnet hlms and described the visualization mechanism. 

The VBLs represent stable magnetic vortices and separate domain wall regions of opposite polarity [76]. The VBL sizes in many typical ferrite-garnet hlms do not exceed tenths of a micrometer. 

Chemical Vapor Deposition. In chemical vapor deposition (CVD), often referred to as vapor transport, the desired constituent(s) to be deposited are ia the form of a compound existing as a vapor at an appropriate temperature. This vapor decomposes with or without a reducing or oxidizing agent at the substrate— vapor interface for film growth. CVD has been used successfully for preparing garnet and ortho ferrite films (24,25). Laser-assisted CVD is also practiced. 

K. J. Standley, "Electrical Properties of Ferrites and Garnets," Oxide Magnetic Materials, 2nd ed.. Clarendon Press, Oxford, UK, 1972. 

So-called hexagonal ferrites such as BaFe -Oi9 are ferrimagnetic and are used to construct permanent magnets. A third type of ferrimagnetic mixed oxides are the garnets, Mj FejOjj, of which the best known is yttrium iron garnet (YIG) used as a microwave filter in radar. 

In the ceramics field many of the new advanced ceramic oxides have a specially prepared mixture of cations which determines the crystal structure, through the relative sizes of the cations and oxygen ions, and the physical properties through the choice of cations and their oxidation states. These include, for example, solid electrolytes and electrodes for sensors and fuel cells, ferrites and garnets for magnetic systems, zirconates and titanates for piezoelectric materials, as well as ceramic superconductors and a number of other substances... 

Garnet ferrites, 11 55, 56t, 57 Gamet-hydrogarnet solid solution series, 5 479t... 

Most transition elements are available in a pure state as metals which can be dissolved in acids. A mixture of nitrates can be evaporated to dryness and calcined to form precursor oxide mixtures for the preparation of spinel and garnet ferrites. Alternatively, mixed oxides, carbonates or oxalates can be precipitated. Microwave ferrites that are required to be of high purity can be prepared by one of these chemical routes. 

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