Magnetic properties of melt-spun Nd-Fe-Co-B-Cu-Nb system alloys and their bonded magnets

Melt-spun ribbons of Nd-Fe-Co-B-Cu-Nb system alloys were prepared by the single roller rapid-quenching method. The effects of composition, wheel velocity and heat-treatment on the magnetic properties were investigated. The magnetic properties of bonded magnets prepared by compression molding of optimally annealed ribbons were also measured. A maximum energy product of 152.1 kJ/m³ was obtained for the Nd₁₁Fe₇₂Co₈B_7.5Cu_0.5Nb_1.0 alloy ribbon prepared at a wheel velocity of 17.1 m/s. From the TEM observation on the above Nd₁₁Fe₇₂Co₈B_7.5Cu_0.5Nb_1.0 ribbon, the particle size of these ribbons was determined to be between 10 and 40 nm. It is conjectured that the high remanence is observed by the magnetic interaction of these fine particles, and it was found that these fine particles were achieved by Nd-Fe-Co-B compound in addition with Nb and Cu at the same time. The amorphous Nd₁₁Fe₇₂Co₈B_7.5Cu_0.5Nb_1.0 ribbons prepared at a wheel velocity of 20.7 m/s were crystallized by heat treatment, and the optimum annealing condition was found to be at 650°C for 15 min. Its corresponding value of (BH)_max is 144.5 kJ/m³. A maximum energy product of 88.1 kJ/m³ was achieved with Nd₁₁Fe₇₂Co₈B_7.5Cu_0.5Nb_1.0 bonded magnets made from the optimally prepared ribbons.