Abstract
Effects of crystallization conditions on magnetic properties have been investigated in amorphous Nd-Fe-B ribbons. Amorphous Nd15Fe75B10 ribbons were obtained by the single roller quenching technique. These ribbons, which have improved ductility and tensile strength, are soft magnetically in the as-prepared state and can be hardened by crystallization. It is found that short time annealing at high temperature is desirable for crystallization to obtain good hard magnetic properties. X-ray diffraction analyses and SEM observations have revealed that flash crystallization results in precipitation of sub-micron Nd2Fe14B micro-crystals whose sizes are nearly that of a single domain particle, and in extremely high coercive force. Excessive annealing at high temperature causes growth of crystallites and reduction of coercive force. The ribbons crystallized in the best condition are magnetically isotropic and have Br of 7kG and (BH)max of 10.2 MGOe when magnetized by a pulse field of about 30 kOe.
