Exchange coupled Nd_2Fe_(14)B/alpha-Fe nanocomposite magnets with fine alpha-Fe grains obtained by low wheel speed spinning

摘要

Exchange coupled Nd_2Fe_(14)B/alpha-Fe nanocomposite magnets have been synthesized by melt-spinning. The effect of wheel speed on the magnetic properties and microstructure has been studied. The results show that a uniform Nd_2Fe_(14)B/alpha-Fe nanocomposite structure with fine alpha-Fe grains can be developed at an optimum wheel speed of about 12 m/s. After a low temperature annealing, the magnetic properties can reach maximum values: _iH_c =432.2 kA/m, J_r = 1.08 T, (BH)_(max) = 115 kJ/m~3. With further increasing the wheel speed, the volume fraction of an amorphous phase increases. The microstructure of the ribbons becomes nonuniform after a subsequent high temperature crystallization, and several alpha-Fe grains abnormally grow to about 100 nm, deteriorating the magnetic properties of the ribbons.