Intrinsic coercive field

Fig. 6.23. Comparison between (a) induction, B, and (b) magnetisation, M, curves, as a function of applied field to illustrate the difference between coercivity, gH,. and intrinsic coercive field, iH-...

In Figure 13 the relation between the intrinsic coercivity and the particle diameter dis given. The figure is based on a described model (35). The maximum is found around the critical particle diameter. In general the particle diameter and size is not very well defined. For the multidomain particles (d > ) the is smaller than the intrinsic anisotropy field of the particle. Nucleation effects cause a decrease in as the increases. This behavior is... 

A second type of behavior existing in the PLZT s is the linear (Pockels) effect which is generally found in high coercive field, tetragonal materials (composition 3), This effect is so named because of the linear relationship between An and electric field. The truly linear, nonhysteretic character of this effect has been found to be intrinsic to the material and not due to domain reorientation processes which occur in the quadratic and memory materials. The linear materials possess permanent remanent polarization however, in this case the material is switched to its saturation remanence, and it remains in that state. Optical information is extracted from the ceramic by the action of an electric field which causes linear changes in the birefringence, but in no case is there polarization reversal in the material. 

In early studies, Sagawa et al. (1984a,b) already pointed out the effects of additives such as Co and Dy on improvements of the magnetic properties, especially the Curie temperature (Tc) and coercivity (Hcj), respectively, of Nd-Fe-B sintered magnets. Dy addition increases the intrinsic anisotropy field, which results in an increase of coercivity. The disadvantage of Dy addition, however, is the high cost of dysprosium. 

Tissier et al. estimated that about 10 Dy atoms are involved in each jump, indicating domain sizes between 10 and 10 um. From the theoretical side several attempts have been made (Cochrane et al., 1978 Ferrer et al., 1978) to calculate coercive fields as an intrinsic property of the microscopic RAM Hamiltonian (eqs. 29-31, though the results seem less satisfactory than those pertaining to the high-field magnetization curves. 

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