Effect of Cu doping and annealing treatment on the microstructure and magnetic properties of nanocrystalline single-phase Nd-Fe-B alloys

The effects of Cu addition and annealing treatment on the magnetic properties and microstructure of Nd_12.3Fe_81.7–xCu_xB₆ (x=0–1.2) ribbons melt-spun and annealed were systematically investigated by the methods of vibrating sample magnetometer (VSM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). Optimum magnetic properties were achieved by annealing melt-spun Nd_12.3Fe_81.5Cu_0.2B₆ ribbons at 550°C for 15 min, which only contained Nd₂Fe₁₄B phase. The remanence, coercive force, and maximum energy product increase by 18.4%, 36.2%, and 49% respectively compared with those of Cu-free samples. The significant improvement in magnetic properties originates from the finer grains of the samples by introducing Cu, which leads to the stronger exchange-coupling between neighboring grains.