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

摘要

Microstructure and magnetic properties of melt-spun Fe_(80-x)Pt_(x)B_(20) (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 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 γ_(1)-FePt, fcc γ-FePt, and Fe_(2)B 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 (_(i)H_(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 γ_(1)-FePt and soft magnetic fcc γ-FePt or Fe_(2)B phases.