Structural and magnetic properties of Sm(Co0.7Fe0.1Ni0.12Zr0.04B0.04)(7.5) melt spun isotropic and anisotropic ribbons

We investigated the structural and magnetic properties of Sm(Co0.7Fe0.1Ni0.12Zr0.04B0.04)(7.5) melt spun ribbons. Samples were arc melted then melt spun at 37 m/s up to 55 m/s to obtain ribbon for powdering. Annealing was performed in argon atmosphere for 30-75 min at 600-870 degrees C. In as-spun ribbons the hexagonal SmCo7 (TbCu7-type of structure) of crystal structure was determined from x-ray diffraction patterns, while fcc-Co has been identified as a secondary phase. After annealing, the 1:7 phase of the as-spun ribbons transformed into 2:17 and 1:5 phases. X-ray patterns for as-milled powders exhibited very broad peaks making it difficult to identify a precise structure but represented the 1:7 structure after annealing at low temperature (650 degrees C). TEM analysis showed a homogeneous nanocrystalline microstructure with average grain size of 30-80 nm. Coercivity values of 15-27 kOe were obtained from hysteresis loops traced up to a field of 5 T. The coercivity decreased as temperature increases, but it maintained values higher than 5 kOe at 380 degrees C. The maximum energy product at room temperature increased, as high as 7.2 MGOe, for melt-spun isotropic ribbons produced at higher wheel speeds. Anisotropic ribbons had a maximum energy product close to 12 MGOe.