Synthesis and magnetic properties of Fe-Pt-B nanocomposite permanent magnets with low Pt concentrations

Microstructure and magnetic properties of melt-spun Fe80-xPtxB20 (x=20,22,24) alloy ribbons have been investigated. A homogeneous nanoscale mixed structure with amorphous and fcc gamma-FePt phases was formed in the melt-spun ribbons. The average sizes of the amorphous and fcc gamma-FePt phases are about 5 nm, and the enrichment phenomenon of B is recognized in the coexistent amorphous phase. The melt-spun ribbons exhibit soft magnetic properties. The nanocomposite structure consisting of fct gamma(1)-FePt, fcc gamma-FePt, and Fe2B phases was obtained in the melt-spun ribbons annealed at 798 K for 900 s, and their average grain sizes are about 20 nm. The remanence (B-r), reduced remanence (M-r/M-s), coercivity (H-i(c)), and maximum energy product (BH)(max) of the nanocomposite alloys are in the range of 0.93-1.05 T, 0.79-0.82, 375-487 kA/m, and 118-127 kJ/m(3), respectively. The good hard magnetic properties are interpreted as resulting from exchange magnetic coupling between nanoscale hard fct gamma(1)-FePt and soft magnetic fcc gamma-FePt or Fe2B phases. (C) 2004 American Institute of Physics.