Magnetic hexagonal ferrite

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. 

A typical hexagonal ferrite is BaFei Oiy- Again, oilier magnetic ions, such as manganese, cobalt, and nickel may be introduced lo produce wide variations in M and T Hexagonal ferriles are characterized by large... 

During the 1930s the Philips researchers in The Netherlands made important contributions to the science and technology of ferrites, especially the pioneer, J.L. Snoek who, in the West, saw the industrial significance of ferrites as telecommunications was rapidly advancing. The development of the magnetically hard hexagonal ferrite ( Ferroxdure ) is also due to Philips [5]. 

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. 

The crystallographic structure of hard ferrites is such that the magnetically preferred (i.e., easy) orientation is the c axis, i.e., perpendicular to the basal plane. Consequently, hexagonal ferrites have been further classified as being either isotropic or anisotropic depending on whether the grains... 

Magnetic ceramics are ferrimagnetic and are classified according to their crystal structure into spinels, hexagonal ferrites, and garnets. 

Albanese, G., Carbucicchio, M., Pared, L., Rinaldi, S., Licchini, E. Slokar, G. (1980). Magnetic and Mossbauer study of Al, Ga, In and Sc-substituted Zn2 W hexagonal ferrites. Journal of Magnetism and Magnetic Materials, 15-18, 1453. 

X-type hexagonal ferrites. Journal of Magnetism and Magnetic Materials, 31-34, 803-4. 

Samaras, D., Collomb, A., Hadjivasiliou, S., Achilleos, C, Tsoukalas, J., Pannetier, J. Rodriguez, J. (1989). The rotation of magnetization in the BaCojFeigOjT W-type hexagonal ferrites. Journal of Magnetism and Magnetic Materials, 79, 193-201. 

Hibst, H. (1982). Hexagonal ferrites from melts and aqueous solutions, magnetic recording materials. Angewande Chemie, International Edition in English, 21, 270-81. 

Lotgering, F. K., Vromans, P. H. G. M. Huyberts, M. A. H. (1980). Permanent-magnet material obtained by sintering the hexagonal ferrite W = BaFeig027. Journal of Applied Physics, 51, 5913-18. 

Hexagonal ferrites possess a wide range of magnetic properties Curie... 

Lilot, A. P., Gerard, A. Grandjean, F. (1982). Analysis of the superexchange interaction paths in the W-hexagonal ferrites. IEEE Transactions on Magnetics, MAG-18, 1463-5. 

The outcome of these two interactions is the ferrimagnetic structure. In general, therefore, ferri-magnetic compounds have a common cation in two valence states and two sets of different sites over which these cations are ordered. Many crystalline structures potentially fulfil these requirements, including the cubic and hexagonal ferrites, described in Sections 12.3.5 and 12.3.6. 

Hard magnetic materials have rather rectangular, broad, hysteresis curves (Figure 12.16). These materials are used in permanent magnets, with applications from door catches to electric motors. The hexagonal ferrites are hard magnetic materials, as are alloys such as SmCos and Nd2Fei4B. 

Estimate (a) the saturation magnetisation and (b) the magnetic inductance for the hexagonal ferrite ferroxdur , BaFei20i9. The hexagonal unit cell has parameters flo = 0.58836 nm, cq = 2.30376 nm and volume 7.128 x 10 m. There are two formula units in the unit cell. Assmne that the orbital angular momentum is completely quenched in this material. 

Magnetoplumbite (hexagonal ferrites) 1 MeOieFejOa MeO = divalent metal oxide from group IIA e.g., BaO, CaO, SrO Hard magnets... 

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