Magnetization Processes in melt-spun Sm-Co-based alloys with the TbCu7-type structure

The initial magnetization processes in melt-spun Sm-Co alloys with remanent ratios above 0.7 have been studied. Alloys of (Sm₁(6+x)/Co_(5+x)(6+x)/)₉₄Nb₃C₃ (x=0.67, 1.7, 2.3 and 3) alloys modified with Nb and C were melt spun at wheel speeds of 20 and 40 m/s, and the compositions span the range between the Sm₂Co₁₇ and SmCo₅ stoichiometries. Structurally, all alloys formed in the TbCu₇-type structure, although a small amount of Sm₂Co₇ was observed in Sm-rich samples, and a small amount of fcc Co formed in Co-rich samples. From transmission electron microscopy analysis, grain sizes typically ranged from 100 to 500 nm, and the grains were randomly oriented. The as-spun ribbons had remanence ratios of 0.7 and coercivity values ranging from 3 to 18 kOe. The initial magnetization curves showed a steep linear response to the applied field for all samples, suggesting that nucleation-controlled processes dominate the magnetization process. In addition, the initial susceptibility decreased with increasing Sm content, reflecting the anisotropy differences between SmCo₅ and Sm₂Co₁₇ compounds. The initial susceptibility also increased with increasing wheel speed, suggesting that the microstructure has important ramifications on the magnetization process as well.