Magnetic properties of αFe/NdFeB nanocomposite alloys prepared by two-step rapid solidification

In order to obtain directly powders of nanocomposite alpha Fe/NdFeB alloys with the composition of NdxFebalCo8NbyBz, where x: 8.0-8.5, y: 1.5-2.5, z: 6.0-6.5 in at%, have been prepared using the two-step rapid solidification apparatus, which is composed of a gas atomizing system at the upper side and a collision-and-solidificating rotor system at the lower side. It is found that the coercivity (HcJ) of flat-shaped powders obtained depends on powder sizes. The best HcJ in each sieved powder is 525 kA/m (6.60 kOe) for a size more than 500 mu m, 449 kA/m (5.64 kOe) for 150-500 mu m, and 391 kA/m (4.91 kOe) for 50-150 mu m. These values are not so high compared to those of powders of ribbons prepared using a single-roller melt spinning apparatus. This should be attributed to the powder size distribution that causes fluctuation of the quenching rate. Thickness of the flat powder is found to be controllable up to 70 mu m, which is useful to get compression molded bonded magnets with a high density and thus a high remanence (Br). An epoxy-bonded magnet with (BH)max: 61.8 kJ/m(3) (7.76 MGOe), Br: 0.732 T (7.32 kG), HcJ: 427 kA/m (5.36 kOe), and density of 6.20 Mg/m(3) is obtained.