Effects of Crystallization Conditions on Magnetic Properties of Crystallized Nd-Fe-B Ribbons

The effects of crystallization conditions on the magnetic properties of originally amorphous Nd-Fe-B ribbons were investigated. Amorphous Nd15 Fe75 B10 ribbons were obtained by the single-roller quenching technique; these ribbons, with improved ductility and tensile strength, are magnetically soft in the as-prepared state and can be hardened by crystallization. It was found that crystallization by annealing for a short time at high temperatures is desirable to obtain good hard magnetic properties. X-ray diffraction analyses and SEM observations revealed that flash crystallization results in precipitation of sub-micron Nd2 Fe14 B microcrystals, whose sizes are nearly that of a single-domain particle, and which exhibit extremely high coercive forces. Extended annealing at high temperatures causes growth of crystallites and lowering of the coercive force. Ribbons crystallized under optimum conditions are magnetically isotropic with a Br of 7 kG and a (BH)max of 10.2 MGOe when magnetzed by a pulse field of about 30 kOe.