what is the reason behind the terms used in Law of approach to saturation ?
The method adopted to deduce the anisotropy constant from the hysteresis loop is questionable, although it has been adopted in some cited works on micro- and nanoparticles. The empirical law of approach to saturation is indeed a rough method to estimate anisotropy from (initial) magnetization curves of bulk polycrystalline materials. Equation (2) is an empirical law that applies to the case of a ferromagnet consisting of randomly oriented single-domain crystallites, with the initial state characterised by M=0. If the system starts from a remnant state (as in the hysteresis loops shown in this work), the numerical coefficients of the law should be different, as explained in J. F. Herbst and F. E. Pinkerton, Phys. Rev. B 57 (1998) 10733. Moreover, the adopted first numerical coefficient (0.07619) holds for the case of independent particles (not interacting).
A spurious contribution could also arise from the possible rotation of nanoparticles under the effect of an applied field. To sum up, the applicability of this analysis to the system studied in this work is uncertain, considering that the nanoparticles actually form agglomerations and thus a strong interaction between them should occur.
Article Strain-induced high coercivity in CoFe2O4 powders
I agree with yuu. However this is model based and would give an indea of the anisotorpy.
I think your question should be directed to the authors in a first place.
The approach to ferromagnetic saturation is generally used to determine the effect of defect structure in the process of magnetization in both the amorphous materials and nanocrystalline (here is somewhat more complicated). Of course, it was originally used for crystalline materials (polycrystalline). I do not know the job but with a summary that there studying materials from the amorphous matrix. Long term milling led to nanokrystalization and amorphization. As for the conglomeration is agree with that. I'll see tomorrow the job and would be happy to write again.
Can the law of approach be used for the determination of anisotropy constant of superparamagnetic materials?
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