Nucleation and growth processes of α-Fe nanocrystals in amorphous NdFeBCoDy: In situ x-ray diffraction studies

For a detailed understanding of formation processes of nanocrystals in an amorphous matrix, the study of crystal nucleation and growth processes is of basic interest. In the present study, these processes of α-Fe nanocrystals in amorphous NdFeCoDyB have been studied separately by employing in situ high-temperature x-ray diffraction measurements. A small growth activation energy Eg=(1.8±0.2)eV was determined from the isothermal time dependence of the grain size of α-Fe crystals. By these data together with the nucleation activation energy En=(3.0±0.1)eV, a coarse grain size for the α-Fe phase in the α-Fe∕Nd2Fe14B nanocomposites developed from amorphous NdFeBCoDy can be understood.