Cubic ferrites

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. 

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,... 

Hydrothermal Method. Iron [Fe(III)], barium, and the dopants are precipitated as their hydroxides and reacted with an excess of sodium hydroxide solution (up to 6 mol/L) at 250-350 °C in an autoclave. This is generally followed by an annealing treatment at 750-800°C to obtain products with the desired magnetic properties. Many variations of the process have been described [5.36]-[5.40], the earliest report being from 1969 [5.41], In later processes, hydrothermal synthesis is followed by coating with cubic ferrites, a process resembling the cobalt modification of iron oxides (see Section 5.1.2). The object is to increase the saturation magnetization of the material [5.42]-[5.44],... 

Table 4 Lattice constants and magnetic properties of some cubic ferrites...

The electronic, structural, and magnetic properties are strongly modified near and at the surface of nanosized cubic ferrite particles. The origin of the surface effects is mainly attributed to the breaking of the translational crystal symmetiy at the... 

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

Soft (cubic) ferrite.s with high permeabilities are used as toil- and tran.sformer-cores... 

The most important application of cubic ferrites, quantitywise, is the manufacture of coil- and transfomier-cores. In terms of numbers, recording and erasure heads for tape recorders, ferrite antennae for the frequency range 0.5 to 1.5 MHz and other components for high frequency technology are also important. 

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. 

Derive a formula for the saturation magnetisation of a cubic ferrite A Fe204, which is only partly inverse. The fraction of Fe " " ions on tetrahedral sites is given by A, where 0 < A < 0.5 (see Section 5.3.10). [Note derivation is not given in the answers at the end of this book.]... 

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

In terms of crystal structure, explain the source of ferrimagnetism for cubic ferrites. 

Cubic ferrites have the inverse spinel crystal structure, which is cubic in symmetry and is similar to the spinel structure (Section 12.2). The inverse spinel crystal structure might be thought of as having been generated by the stacking of close-packed planes... 

Cubic ferrites having other compositions may be produced by adding metallic ions that substitute for some of the iron in the crystal structure. Again, from the ferrite chemical formula M 0 -(Fe )2(0 )3, in addition to Fe ", may represent... 

For cubic ferrites, the net magnetization results from the divalent ions (e.g., Fe ) that reside on octahedral lattice sites, the spin moments of which are all mutually aligned. 

The stainless steel is composed of chromium and Fe-C base alloys which are used due to their pitting resistance. To maintain a body centred cubic ferritic structure, a minimum of 13% chromium is required. Stainless steels can be categorised into duplex, austenitic, ferritic, and martensitic. Carbon and nitrogen are austenitic formers and characterised by a y-austenitic face-centred cubic. For planar SOFC, the stainless steels should contain Cr content 17% considering the fact that chromium may be depleted by interaction with adjoining components. 

---