A series of alloys was prepared to investigate the crystallization of Co-rich HiTPerm-type alloys ͓͑Co 1−x Fe x ͒ 88 Zr 7 B 4 Cu 1 ͔ with Fe:Co ratios within or near the two-phase ͑bcc+ fcc͒ region of the binary phase diagram. The goal of this work is to better understand the phase evolution and crystallization of alloys in which the Fe-Co binary phase diagram predicts more than one transition metal rich primary crystalline phase to be present in equilibrium at the primary crystallization temperature. X-ray diffraction, transmission electron microscopy, and high-temperature vibrating-sample magnetometry have been performed to identify the first phase to crystallize and to follow the evolution of phases during crystallization. The bcc phase appears to be the primary crystalline phase that forms first after annealing at 450°C for 1 h, in agreement with previous work on Co-rich nanocomposite alloys. We observe that as the Co concentration is increased, the fcc crystalline phase forms at lower annealing temperatures and its volume fraction increases for a given annealing temperature.

Crystallization and field-induced magnetic anisotropy were investigated for a Co 89 Zr 7 B 4 alloy. A mixture of nanocrystalline fcc and hcp phases surrounded by an amorphous matrix is present after primary crystallization. For annealing in a 2 T transverse field, the observed anisotropy fields and field-induced anisotropies are H K ϳ 12-15 Oe and K U ϳ 550-680 J / m 3 for field annealed amorphous ribbons as compared to H K ϳ 18-19 Oe and K U ϳ 800-850 J / m 3 for field crystallized ribbons. In comparison with the corresponding Fe-based alloy, the relatively high Curie temperature and large field-induced anisotropy of the field annealed amorphous ribbons indicate that the intergranular amorphous phase may provide a relatively more significant contribution to the field-induced anisotropy of Co-based nanocomposite ribbons such as Co 89 Zr 7 B 4 .