THE EFFECT OF MICROSTRUCTURAL EVOLUTION ON THE COERCIVITY DEVELOPMENTOF PT-CO-B ALLOYS

The undercool-rapid-quench (URQ) processing of Pt42Co45B13 (at. %) (Pt -Co-B) alloys with subsequent annealing produced an intrinsic coercivi ty (H(ic)) as high as 15.7 kOe. The evolution of H(ic) during heat tre atment is related to the initial URQ-processed microstructure and its influence on the annealing phase transformations. Higher solidificatio n rates refine the dendrites, decrease the interdendritic volume fract ion, and enrich the interdendritic boron concentration. Annealing the materials processed with a higher quenching rate leads to more rapid i nterdendritic decomposition with more refined transformation products and a concomitant larger increase in H(ic). The high H(ic) in Pt-Co-B alloys originates mainly from difficult magnetic domain nucleation owi ng to limited nucleation sites in magnetic single-domain size Co3B pre cipitates and an ordered magnetic anisotropic matrix with few defects such as antiphase domain boundaries and twins.