A possible method would be to utilize neutron diffraction as it is very accurate and your samples are bulk so its a good fit. Plus it gives an excellent contrast w.r.t. magnetic states of individual atoms, so complex structures should be easy to interpret.

I hope it helps.

Thanks for the advice. I'm interested in the interpretation of the structure of the amorphous material.

All your questions are just as interesting, as difficult and raise very fundamental problems. And in this case, You, probably, meant the reconstruction (recreating) of the magnetic structure (identification or clarification the domain structure picture). As for neutron diffraction analysis, its spectra are very difficult to interpret even for known crystal structures.