In a double perovskite system with three different calcination temperatures shows a hysteresis loop but there was a drastic decrease in magnetic moment with respect to an increase in calcination temperature. I was wondering whether it should be concluded that AFM ordering took place or something else? Any references will be appreciable.
Look at the details of the B-cation disorder (as obtained from refinement of diffraction data), microstructure of the sample, oxygen vacancies and the presence of the impurities if any.
Pls. treat it as an academic discussion with no excellence proclaimed.
[1] I will, humbly, agree with your argument that the primary reason is the change in AFM nature of the DP. It is already very well argumented that the calcination can cause change the unit cell structures which may change M---O--- M distances. As AFM is highly dependent on these distances and thus there may occur change in magnetic character.
[2] Taking a cue from the idea of respected DrFalak Sher ( though I not a researcher in the true sense], may I suggest?
(i) to try ESR to quanify oxygen vacancies[ Some suggest Oxygen back scattering; but I have simply heard about it] and explore an explanation for change in AGM and thus the magnetic moment.
(Ii) try Mossbauer if iron is present. AFM six line pattern should change wrt to 1,6 and 3,4 line widths. Rather, my humble submission will to try Mossbauer at different temperatures. Who knows that the sextet at LNT may change to a singlet at Tc?
Are you taking about double perovskite manganites? If so what is your calcination temperatures range? Normally for this system magnetism is due to Mn3+/Mn4+ population. Calcination temperature may change their ratio due to oxygen vacancies as Prof. Falak Sher discussed. As a result magnetic property may varied.
Yes. The material is double perovskite calcinated to 600, 700 and 800 deg C. The Ms for 600 is 1.24 emu/g. But Ms for 700 and 800 was 0.01724 emu/g and 0.0125 emu/g. But all shows good hysteresis.
According to my point view, the variation of cation/anion vacancy or oxygen vacancies with respect to temperature are one of the significant factor in both mono/double pervoskites as some of them gave enough explanations already sir.
Do you mean by "good hysteresis" that the coercivity is appreciable in all samples? Would an antiferromagnet have a hysteresis loop?
Anyway, the temperature dependence of the susceptibility for an AFM is distinctly different from that for a PM or a FM material. Specifically, the inverse susceptibility for an AFM would intercept the temperature axis at a negative temperatur, while that for a FM intercepts the axis at a positive temperature and for a PM the line goes through the origin.
Your samples seem to have very low Ms. What is your saturating magnetic field?Have you performed any structural characterization? Are they single phase? What are the starting materials for your compositions? Calcination temperatures are also seem low to me.
With different words, all of us are of the opinion that that what ever may be metal ion [ Fe or Mn], the decrease in magnetism is due to the difference in the extent of AFM{ as Dr Ravi has himself hinted}. I make a humble submission to try ESR for ascertaining the oxygen vacanc ies.Again, most of us must be knowing that all we have to do is take first derivative ESR spectra of the three calc ined products[ obtained at three different temperatures] and would find the areas of the peaks by applying the following relation to quatify the oxygen vacancies and thus the loss of magnetism provided the shapes of the peaks are identical.
A=w ^2.h
Where A= area, w= width; h= height of the peaks respectively.
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