Nanocrystallization and magnetic properties of amorphous Nd9Fe85B6 subjected to high-pressure torsion deformation upon annealing

A high number density (∼1023 m−3) of α-Fe nanocrystals with a size below 10 nm has been induced in amorphous Nd9Fe85B6 by high-pressure torsion deformation (HPTD) at room temperature. The amorphous Nd9Fe85B6 subjected to HPTD presents a quite different crystallization behavior as compared with the nondeformed alloy. The growth activation energies Eg=0.9 eV for α-Fe nanocrystals and 0.5 eV for Nd2Fe14B nanocrystals are determined from the annealing time dependence of their size. The α-Fe/Nd2Fe14B nanocomposite magnets prepared by the combination of HPTD and subsequent thermal annealing show enhanced magnetic properties due to a small grain size as compared with the magnets prepared by directly annealing amorphous Nd9Fe85B6.