Structural and magnetic coherence lengths in FePC(Cr) amorphous alloys

Abstract

Neutron scattering techniques have been used to study the structural and magnetic coherence lengths in two FePC(Cr) amorphous alloys. It is found that whereas the loss of long range magnetic order at the Curie temperature is clearly shown by the critical divergence of neutron scattering at low angles, there is no significant discontinuity in the scattering at this temperature elsewhere. Detailed analysis of the temperature dependence of the scattered intensity in the region of the first peak in the structure factor suggests that essentially all the variation observed is due to evolution of the temperature dependent nuclear scattering. These results suggest that even in the paramagnetic state the spins on the iron atoms remain ferromagnetically correlated over distances at least as great as the structural coherence length. The analysis underlines the danger of deducing the magnetic scattering in amorphous alloys from the difference between diffraction patterns obtained above and below Curie temperature.