Fe-B/FePt-type nanocomposite ribbons with high permanent magnetic properties

The Fe-B/FePt-type nanocomposite ribbons with strong exchange-coupling and high permanent magnetic properties have been developed by the melt-spinning method. For binary Fe50+xPt50−x (x=0-20) ribbons spun at 45 m/s, followed by a 500 °C isothermal annealing, an ordered magnetically hard γ1(FePt) phase can be fully formed at x⩽10, but the coercivity is merely of less than 2.0 kOe. Nevertheless, for ternary (Fe0.5+yPt0.5−y)zB100−z (y=0-0.2; z=82 and 84), multiple phases, namely γ1, Fe2B and Fe3B, with nanoscaled grain sizes (25-35 nm) can readily form in ribbons after an isothermal annealing at 500 oC. Strong exchange-coupling between grains was found in these ribbons, giving rise to an enhancement of not only the remanence but also the maximum energy product. AiHc of more than 12 kOe has been obtained in (Fe0.6Pt0.4)82B18 (Br=6.6 kG, (BH)max=8.9 MGOe), while a new record with a Br of 9.4 kG, iHc of 7.5 kOe and (BH)max of 14.0 MGOe can be achieved in (Fe0.675Pt0.325)84B16.