How can I obtain correctly DC demagnetisation curve (for nanoparticles)?
How should I specifically perform the measurements:
a) Do I bring to saturation my sample once and then apply increasingly larger (in incremental steps) magnetic field;
b) I have to bring back sample to saturation before every incremental step in H (to get the field dependence as in point a)?
Any good reference to read more, please?
As far as I know, the DCD curve is nothing else but an upper branch of quasistatic hysteresis loop (so the external field decreases rather than increases). Why 'quasistatic'? Because of --> magnetic viscosity. This term refers to both: to the sample and to the electromagnet's poles (I'm not sure whether magnetic viscosity is at play with superconducting magnets). A single nanoparticle will adapt itself to changing exciting field within few nano- or microseconds, but massive magnet's poles may need few second, maybe up to 1-2 minutes. How long will it take for a powder (many nanoparticles) to 'relax' after the field is changed? Only careful experiment will show.
One more important point: make sure that your nanoparticles cannot move (or reorient themselves) during a measurement!
See
Article The structure and magnetic properties of cobalt ferrite nano...
The following article may help you
Wang, S., Kang, S.S., Nikles, D.E., Harrell, J.W. and Wu, X.W., 2003. Magnetic properties of self-organized L10 FePtAg nanoparticle arrays. Journal of magnetism and magnetic materials, 266(1-2), pp.49-56.
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