Ferrites hexagonal

Ferrites can be classified according to crystal stmcture, ie, cubic vs hexagonal, or magnetic behavior, ie, soft vs hard ferrites. A systematic classification as well as some appHcations ate given in Table 1 (see also Magnetic materials, bulk Magnetic materials, thin film). 

Fig. 1. Composition diagram for hexagonal ferrites where B = BaFe2 04, M = BaFej2 O g, S = MeFe2 04, T = BaFe O, W = BaMe2Fejg O27,...

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. 

The family of structurally related hexagonal ferrites contain intergrowths of these elemental building blocks S, R and T. 

Another hexagonal ferrite of interest is KFenOn, which has a structure similar to that of magnetoplumbite except for the FeBa03 layers, which are replaced by KO layers, see Fig. 15. 

The ferrites generally have one of three crystal structures inverse spinel, gameL and hexagonal. The spinel structures (cf. 

The hexagonal ferrites have a structure related to the spinel structure but with hexagonal close-packed oxygen ions and a unit cell made up of two formulae of MN12O19, where M is divalent (Ba, Sr, or Pb) and N is trivalent (Al, Ga, Cr, or Fe),... 

The structure of so-called hexagonal ferrite is based on the spinel (MgAljOJ structure. Arrangement of oxygen in spinel is CCP, and Mg and... 

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]. 

---