High coercivity in boron substituted Sm-Co melt-spun magnets

The structural and magnetic properties of nanocomposite melt-spun Sm(Co/sub 0.74-x/Fe/sub 0.1/Cu/sub 0.12/Zr/sub 0.04/B/sub x/)/sub 7.5/ magnets have been investigated as a function of boron content (x = 0.005 0.05), wheel speed and annealing conditions. The as-spun ribbons are nanocrystalline with fine microstructure and average grain size of 60-100 nm. X-ray diffraction indicates that the as-spun samples have the metastable hexagonal TbCu/sub 7/-type structure phase and fcc-Co as a secondary soft phase. Magnetization at nonsaturating 5 T field is 45-72 emu/g and the reduced remanence (Mr/Ms) is above 0.8. The loop shape exhibits a characteristic step due to the soft magnetic phase. At room temperature, Hc values of 20-28 kOe are obtained for as spun samples, with a record value of 38.5 kOe for x = 0.04. At 380/spl deg/C Hc values higher than 5 kOe are observed. Coercivity and loop shape are strongly dependent on annealing conditions.