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

Abstract

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 γ-FePt phases was formed in the melt-spun ribbons. The average sizes of the amorphous and fcc γ-FePt phases are about 5nm, 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 γ1-FePt, fcc γ-FePt, and Fe2B phases was obtained in the melt-spun ribbons annealed at 798K for 900s, and their average grain sizes are about 20nm. The remanence (Br), reduced remanence (Mr∕Ms), coercivity (Hci), and maximum energy product (BH)max of the nanocomposite alloys are in the range of 0.93–1.05T, 0.79–0.82, 375–487kA∕m, and 118–127kJ∕m3, respectively. The good hard magnetic properties are interpreted as resulting from exchange magnetic coupling between nanoscale hard fct γ1-FePt and soft magnetic fcc γ-FePt or Fe2B phases.