  We have 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
has been performed in argon atmosphere for (30 to 75) min at (600 to 870) oC.
In as-spun ribbons the hexagonal SmCo7 (TbCu7-type of structure) of crystal
structure has been 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 transforms into 2:17 and 1:5 phases. X-ray patterns for
as-milled powders exhibit very broad peaks making it difficult to identify a
precise structure but represent the 1:7 structure after annealing at low
temperature (650 oC). TEM analysis shows a homogeneous nanocrystalline
microstructure with average grain size of (30 to 80) nm. Coercivity values of
(15 to 27) kOe are obtained from hysteresis loops traced up to a field of 5 T.
The coercivity decreases as temperature increases, but it maintains values
higher than 5 kOe at 380 oC. The maximum energy product at room temperature
increases, as high as 7.2 MGOe, for melt-spun isotropic ribbons produced at
higher wheel speeds. Anisotropic ribbons have a maximum energy product close to
12 MGOe.
