Nanoscale microstructure and magnetic properties of melt-spun Sm(Co0.725Fe0.1Cu0.12Zr0.04B0.015)7.4 ribbons

We have investigated the nanocrystalline microstructure and the hard magnetic properties of Sm(Co0.725Fe0.1Cu0.12Zr0.04B0.015)7.4 melt-spun ribbons. The coercivity (Hc) of the as-spun ribbons increased with the wheel surface speed from 2.8 kOe for 10 m/s to 14.5 kOe for 40 m/s. The post-annealing of the melt-spun ribbons from 700 to 900 °C for 10 min did not lead to a substantial increase of Hc. However, after isothermal aging at 820 °C and subsequent slow cooling (0.5 °C/min) to 120 °C, Hc increased from 2.8 to 10.9 kOe for 10 m/s, while it decreased from 14.5 to 13.5 kOe for 40 m/s ribbons. The grain size of the melt-spun ribbon reduced with structural transformation from 2:17H (Th2Ni17-hexagonal type) to 1:7H (TbCu7-hexagonal type) as the wheel surface speed was increased. Three-dimensional atom probe analysis showed a boron enriched precipitate at the grain boundaries in the as-spun ribbons, which acts as the grain growth inhibitor causing the refinement of the microstructure.