Ferromagnetic ferrites

In order to give an example, let us consider a steel sample in which ferrite and austenite phases are present. The standard pattern ( Fe Mbsshauer spectrum) of the sample is a complex spectrum that is a sum of subspectra ( Fig. 25.21). The subspectra of the ferromagnetic ferrite... 

Table 7.8. Properties of selected ferromagnetic ferrites and garnets ...

If Fe atoms occupy the B sites (gray in the figure), they may be ferromagnetic, and known as ferrites, although many of the latter have a different structure, that of magnetite. 

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... 

Ferrite. Iron which, in pig iron or steel, has not combined with carbon to form cementite (FeaC). It exists in a, /9, y and 8 forms, which vary in magnetism and ahility to dissolve cementite. Name also applied to compd NaFe02 (called Na ferrite), to ferromagnetic oxides having a definite cryst structure (spinels) and the formula M++Fe ++04 of which the divalent metal may be Fe, Ni, Zn, or Mn. The magnetic props vary accdg to the divalent atom present, and ferrites are now tailored for their desired effect, as Ni-Al ferrite ... 

The present authors proposed ferromagnetic supports, which can withstand liquefaction environment and conditions by their inherent nature or by protection with a carbon coating (141). Carbon has been recognized as an excellent support for FeS and Ni-MoS as described in the previous section (50). Very fine particles of ferrite are available. Coating with carbon can be performed through precipitation of polymers or pitches by the aid of suspension agents followed by carbonization (Ml). Catalyst deactivation by mineral and carbon deposition should be avoided for this approach to be feasible. 

This relaxation time—which, to be specific, we have written in the Landau-Lifshitz representation—has the anticipated behavior the smaller the precession damping constant (the higher the quality factor of the oscillations), the slower does the particle magnetic moment approach its equilibrium position. For ferromagnet or ferrite nanoparticles the typical values of the material parameters are Is Is < 103G, Vm 10 18cm3, and a 0.1. Substituting them in formula (4.28) aty 2 x 108 rad/Oe s and room temperature, one obtains xD 10-9 s. 

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