Effects of Ti/Zr Substitution and Thermal Annealing on Magnetic Properties of ThMn ₁₂ ‐Type Y/Ce‐Co Melt‐Spun Ribbons

The effects of Ti/Zr substitution, annealing temperature, annealing time, and wheel speed on the phase evolution and magnetic properties of YCo 12‐x Ti x ( x = 0.9, 1.2, 1.5, 1.8, 2.1, and 2.4) and CeCo 12‐z Ti z ( z = 1.3, 1.4, 1.5, 1.6, and 1.7) melt‐spun ribbons were systematically investigated using scanning electron microscopy, X‐ray diffraction, and vibrating sample magnetometer. The results demonstrate the following: (1) For YCo 12‐x Ti x alloys, increasing Ti content stabilizes a single‐phase ThMn 12 ‐type structure at x = 1.8, with melt‐spun ribbons (35 m/s) exhibiting optimal magnetic properties (H cj = 0.37 kOe, B r = 3.03 kGs, μ 0 M s = 6.43 kGs). Excess Ti ( x > 1.8) triggers secondary phases Co 2 Ti(h) and YCo 3 , degrading their magnetic performance. Zr substitution (Y 0.75 Zr 0.25 Co 10.2 Ti 1.8 ) stabilizes the ThMn 12 structure, but enhances the formation of Co 2 Ti(h). (2) Annealing Y 0.75 Zr 0.25 Co 10.2 Ti 1.8 ribbon at 400°C for 30 min optimizes magnetic performance (H cj = 0.69 kOe, B r = 2.71 kGs, μ 0 M s = 5.47 kGs) by balancing crystallinity and grain boundary density. Prolonged annealing (>1 h) or higher temperatures (600–800°C) reduces H cj due to grain coarsening and excessive precipitation of Co 2 Ti(h). (3) For CeCo 10.7 Ti 1.3 ( z = 1.3) and CeCo 10.6 Ti 1.4 ( z = 1.4) ribbons, a wheel speed of 30 m/s maximizes the 1:12 phase fraction in a nanocrystalline/amorphous composite, achieving peak performance (H cj = 0.30/0.22 kOe, μ 0 M s = 8.20/7.69 kGs). Low speeds (20–25 m/s) yield coarse grains and low H cj , while high speeds (35–40 m/s) increase amorphous content, disrupting magnetic order. Optimal magnetic properties of YCo 12‐ x Ti x ribbons with x = 1.8 annealed at 400°C/30 min as well as CeCo 12‐z Ti z ribbons with z = 1.3 (30 m/s wheel speed) were realized, providing insights for designing rare‐earth cobalt‐titanium magnetic materials.