Dear Elangbam, It can be seemed difficult to calculate the magnetic momentum, but one reason is that the understanding of the quantum mechanics has miss the second part of Dirac’s theory. In this paper there is a calculation of the Lande factor allowing the contribution of each quantum state: for example, for one quantum state its magnetic momentum is 1.8µB corresponding to the cobalt magnetic moment of the cobalt see “Total angular momentum and atomic magnetic moments” on my site. You will find the calculation of all the magnetic moment of the rare earth mertals, of several chromium compounds and that of Fe, Co and Ni.

Dear Elangbam,

From practical of view, this depends on which component is dominant. If we consider a ferromagnetic powder, with size distribution ranging from few nanometers to micrometers ones, you have a co-existence of ferro(FM), SPM. Also I think the difference between FM and PM depends on material composition and crystalline phase. As an example of my experience micro Fe3O4 is FM but its nanosize (below 30nm) is SP, while micro Fe2O3 (hematite) and most other (but not all) Fe oxides are weak ferro (WFM0 or PM. So the criteria here is by analyzing XRD test, electron microscopy test, elemental composition test and H-M test. This information may not be found in one two sources, they spreading in some, so that I can not provide a certain one.

Regards

Dear Elangbam,

For Fe-based magnetic alloys in wich the atomic order/disorder or grain size are importat to determine the existence (or co-existence) of FM, AFM, SPM, etc, the Mössbauer effect spectroscopy is an analytical powerfull tool.

Best regards

Thank you all for the kind responses. In fact, I came across the equation describing the MH curve as a combination of FM, SPM and PM which is attached herewith. I could understand the origin/ derivation for FM and PM (separately) but can't understand the FM part (1st term in the given equation). So, I would like to know how FM term was originated/ derived and relevant theoretical background.

With regards

Chitra

Neutron diffraction experiments below FM ordering temperature gives information like atom s magnetic moment.

Study the temperature dependences of magnetic parameters in a wide temperature range.

Dear Elangbam Chitra Devi,

The formula you present is a real headache. Its second term is correct both for paramagnets and superparamagnets as well. The only difference between those two classes of magnetic materials is in the 'elementary' magnetic moment: ~1 Bohr's magneton for paramagnets and ~104--106 Bohr's magnetons for superparamagnets. The last, third term, is fine for those two classes too, but only for fields H close enough to zero. In fact, it simply duplicates the behavior of the second term. However, it never goes to saturation, what is clearly nonphysical and was never observed. The same problem exists with the first term of your equation. In summary: this equation tries to describe the hysteresis loop of magnetic sample but shamefully fails for ferromagnetic components. In fact, the first term presents two parallel straight lines, never saturating (trying to simulate the upper and lower branch of hysteresis loop). In addition, the value of HC looses its meaning (of coercive field) when any of the two other terms is present.

I'm afraid that no paper based on the presented equation will be ever accepted for publication.