Single-crystal ferrites

A detailed investigation about the growth of cobalt ferrite single crystals through a borax flux method and its characterization was reported by Wang and Ren [40]. 

The Raman spectrum of cobalt ferrite single crystals excited by 532 nm laser line, attained at room temperature, is reproduced in Fig. 14.5. By performing the fitting of the Raman spectra displayed in Fig. 14.5, it would be possible to observe Raman bands at 183, 304, 469, 573, 627, and 696, listed in Table 14.2. Apart from Fc304, y-Fe203, and CoFc204, others ferrites such as NiFc204 and Fc3 . Zn - O4 which... 

A simple method of preparing single crystals is to melt the material and to crystallise it by slow cooling but practically all the ferrites dissociate at temperatures below their melting points, with loss of O2. To overcome this problem several techniques have been used which are based on the formation of a flux, a solution, or a volatile chemical compound to obtain ferrite single crystals. 

Ferreti, A., Kunnmann, W. Wold, A. (1963). Growth of ferrous-free cobalt ferrite single crystals. Journal of Applied Physics, 34, 388-9. 

Fig. 4.61. Domain wall velocity as a function of applied field for a Mn-Zn ferrite single crystal at 77 K. (Adapted from Dillon Earl, 1959.)...

Kam] Kamilov, I.K. Mutalipov, M.M., Properties of Ferrite Single Crystals in Strong Steady and Pulsed Electric Fields (in Russian), Izv. Akad. Nauk SSSR, Ser. Fiz., 34(6), 1250-1252... 

Namba, Y., Yamada, Y., Tsuboi, A., Unno, K., and Nakao, H., Surface structure of Mn-Zn ferrite single crystals ground by an ultra-precision surface grinder with various diamond wheels. Annals of the CIRP, Vol. 41, No. 1,1992, 347. 

Vos] Voskanyan, R.A., Growth of Barium Ferrite Single Crystals from Solution in Melts , Sov. 

To distinguish among major fields nt applications, ferrites can he separated into live groups Soft, square-loop. hard, microwave, and single-crystal lerrites. 

Chemical-transport reactions have been used to prepare single crystals of triiron tetraoxide (magnetite) and other ferrites, which comprise the majority of all known ferrimagnetic mate-... 

The garnet ferrites are the basis of materials for many high-technology devices for magnetooptical, microwave and memory applications. These ferrites have thus been extensively studied as ceramics, single crystals, thin and epitaxial films, etc. The prototype, yttrium iron garnet or YIG has also been used for many fundamental studies. 

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. 

Ferrites can be prepared by almost all the existing techniques of solid state chemistry, leading to a very wide variety of forms polycrystalline aggregates, thin and thick films, single crystals. Some of these methods have been developed to prepare ferrites with specific microstructures. The oldest one, the ceramic method, involves the same operations as the classical techniques for fabrication of conventional ceramics. This explains the origin of the term magnetic ceramics. Many of the techniques recently developed consist of improvements in one or several of the basic operations of ceramic fabrication. 

Single-crystal spinel ferrite films can be epitaxially grown on MgO substrates. The ferrite, in a melt with Na2C03 as solvent, is deposited on the substrate at temperatures of 1100-1250 °C. Crystallisation of the... 

Chemical vapour deposition (CVD), or more specifically, organo-metallic CVD can also be used to prepare ferrite thin films (Itoh, Takeda Naka, 1986). A mixture of acetylacetonate complexes of the desired metal is evaporated in a quartz boat (number 1 in Fig. 3.27) and is reacted with O2, which is introduced directly in the deposition zone. By adding a second furnace (B), an additional component evaporating at a different temperature can be transported to the substrate. Glass or MgO single crystals can be used as the substrates an annealing up to 1(X)0°C is performed on the film to improve its crystallisation. Spinel thin films (Ni, Ni-Zn) have been prepared by this method. 

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