Microstructure and magnetic properties of nanocomposite Nd₂Fe₁₄B/α-Fe permanent magnetic powder prepared by mechanical milling

Nanocomposite Nd₂Fe₁₄B/α-Fe magnetic material was prepared by the mechanical milling and a subsequent crystallization vacuum annealing treatment with the as-cast alloy of Nd₂Fe₁₄B atomic ratio and α-Fe. The effects of milling and crystallization conditions on the microstructure and magnetic properties were investigated by X-ray diffractometer (XRD), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM), respectively. It was found that the grain sizes of both the Nd₂Fe₁₄B and the α-Fe phases decreased drastically with increasing the milling time. After milling for 5 h, the as-milled material was comprised of ''-Fe nanocomposite phases of about 10 nm in size and some amorphous phases, which could be turned into the Nd₂Fe₁₄B/α-Fe nanocomposite phases by the subsequent crystallization annealing treatment. High magnetic properties could be achieved by the optimization of crystallization treatment process. In the present study, the best magnetic properties determined by PPMS were B_r=1.06 T, H_ci=347 kA/m, and (BH)_m=142 kJ/m³, respectively, when the material was milled for 5 h, followed by an annealing treatment at 650°C for 30 minutes.