Exchange coupled Nd₂Fe₁₄B/ α-Fe nanocomposite magnets with fine α-Fe grains obtained by low wheel speed spinning

Exchange coupled Nd₂Fe₁₄B/α-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 Nd₂Fe₁₄B/α-Fe nanocomposite structure with fine α-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/m³. 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 α-Fe grains abnormally grow to about 100 nm, deteriorating the magnetic properties of the ribbons.