Crystallization behavior and magnetic properties of Cu-containing Fe-Cr-Mo-Ga-P-C-B alloys

Multicomponent Fe65.5Cr4Mo4Ga4P12C5B5.5 amorphous alloy is known to have good soft magnetic properties combined with large glass-forming ability. Searching for a nanocrystalline structure that could improve its magnetic properties, Cr and Mo were partially substituted by Cu. The devitrification process of Cu-containing alloys shows an additional broad crystallization event that can be described by an Avrami law, with an exponent close to unity, typical for nanocrystallization phenomena. The microstructure of the nanocrystalline alloys consists of Fe(Ga) nanocrystals with a mean grain size of 5-10 nm embedded in an amorphous matrix. The maximum crystalline volume fraction achieved at the end of the nanocrystallization process was found to be of around 20% and for alloys with high Cu content a number of crystals of larger size (similar to 40 nm) were observed. The combined use of x-ray diffraction and Mossbauer spectrometry allowed to estimate the compositions of both the nanocrystalline grains and the amorphous residual phase of nanocrystalline alloys. The complex hyperfine structure of the studied alloys at the end of the nanocrystallization process was characterized. (c) 2006 American Institute of Physics.