Cubic spinel ferrites

Ferrites with the cubic spinel structure (see Section 5.3.10) are soft magnetic materials (see Section 12.4.3), widely used in electronic circuitry. The formula of all ferrites can be written as A +Fe +04, where can be chosen from a large number of medium-sized cations, for example Ni or Zn. The majority of the important ferrites are inverse spinels, in which the cations occupy the octahedral sites, together with half of the Fe + ions. The other half of the Fe cations is found in the tetrahedral sites. Thus nickel ferrite would be written (Fe +)[Ni Fe ]04, where the cations in octahedral sites are enclosed in square brackets and those in tetrahedral sites in parentheses. Lodestone, or magnetite, Fe304, described in Section 12.3.4, is an example in which the cations are Fe and Fe, and the cation distribution is (Fe +)[Fe2+Fe +]204. 

In reality, the distribution of the cations is rarely perfectly normal or inverse, and the distribution tends to vary with temperature. As the magnetic 

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The soft magnetic spinel ferrites, by far the most important cubic ferrites, were first introduced by Philips under the trade name Ferroxcube (14) and are now widely commercially available under various trade names. The world market for soft magnetic ferrites amounts to about one biUion dollars (1991), about 350 million dollars of which is in the United States. 

Spinel Ferrites. In spinel ferrites having the composition where A and B are metals, cubic close-packed oxygen ions leave two kinds of... 

Cubed compound, in PVC siding manufacture, 25 685 Cube lattice, 8 114t Cubic boron nitride, 1 8 4 654 grinding wheels, 1 21 hardness in various scales, l 3t physical properties of, 4 653t Cubic close-packed (CCP) structure, of spinel ferrites, 11 60 Cubic ferrites, 11 55-57 Cubic geometry, for metal coordination numbers, 7 574, 575t. See also Cubic structure Cubic symmetry Cubic silsesquioxanes (CSS), 13 539 Cubic structure, of ferroelectric crystals, 11 94-95, 96 Cubic symmetry, 8 114t Cubitron sol-gel abrasives, 1 7 Cucurbituril inclusion compounds,... 

Fabry-Perot cavity, 14 849, 850 Fabry-Perot etalons, 11 151, 152 Face-centered cube lattice, 8 114t Face-centered cubic (FCC) crystal structure in Ni-base alloys, 13 512 of spinel ferrites, 11 60 Facial makup, 7 846-847 Facial preparations, 7 842t Facial tridendate ligand, 7 578 Facihtated transport, 15 826-827 carrier, 15 845-846... 

The spinel ferrites were fabricated by solid state reaction technique. Cobalt and Zinc ferrites CoxZnyFe204,(x=0.7,0.3,0.4,0.2 and y=0.3,0.7,0.6,0.8) were prepared by solid state reaction technique. The crystalline structure of the sample was investigated by X-ray diffraction(XRD). All samples show cubic spinel structure. The lattice parameter decreases with increasing cobalt content. Magnetic properties shows that the prepared sample exhibit ferromagnetic behaviour at room temperature. The saturation magnetization increases with increasing cobalt content. Curie temperature... 

Figure 1.41) have the oxygen ions in a nearly close-packed cubic array. The unit cell contains 32 oxygen ions, with 32 octahedral and 64 tetrahedral sites, of which 16 of the octahedral and 8 of the tetrahedral sites are filled. It is the position of these 24 cations within the unit cell that determines magnetic behavior. The distribution of cations in the sites is specific to the type of cations, and it must be determined experimentally. There are two idealized spinel structures. In the normal spinel, all the divalent ions are on the tetrahedral sites, as in ZnFe204. In the inverse spinel, the 8 occupied tetrahedral sites are filled with trivalent ions and the 16 occupied octahedral sites are equally divided between di- and trivalent ions (see Figure 6.63). The prototypical inverse spinel ferrite is magnetite, whose structure consists of an FCC oxygen array with Fe + and Fe + ions in the interstices.

Figure 2-44 Microstructure of machinable fenimagnetic glass-ceramic (see the composition in Table 2-22) after heat treatment (1180 C/1 h). Cubic spinel crystal of the ferrite-type and mica crystals characterize the morphology of the glass-ceramic (SEM).

Cubic ferrites crystallizing in the spinel (MgAl204) structure with the general chemical composition... 

Some rather complex crystals can be built on a cubic lattice. For example, the ferrites, which are magnetic and are used as memory cores in digital computers, have the formula MO Fe203, where M is a divalent metal ion like Mn, Ni, Fe, Co, etc. Their structure is related to that of the mineral spinel. The Bravais lattice of the ferrites is face-centered cubic, and the unit cell contains 8 molecules or a... 

Estimate (a) the saturation magnetisation and (b) the magnetic inductance for the cubic ferrite CoFe204 with the inverse spinel stmcture. Co " " is a d ion. The cubic unit cell has a lattice parameter of 0.8443 nm and contains eight formula units. Assume that the orbital angular momentum is completely quenched in this material. 

Spinel (cubic ferrites) 1 MeO IFesOa MeO = transition metal oxide, e.g., Ni,Co, Mn, Zn Soft magnets... 

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