Direct synthesis of L10-(Fe, Co)Pt nanocrystallites from (Fe, Co)-Pt-Zr-B liquid phase by melt-spinning

The ordered Ll(0)-FePt phase with a size of 20 200 nm was directly formed by rapidly quenching the melt in the compositional range of 2-5 at.% Zr and 17-20 at.% B, and the alloys exhibit coercivity (H-c higher than 200 kA/m in an as-quenched state. In particular, the melt-spun (Fe0.50Pt0.50)(78)Zr4B18 alloy exhibits high H, of 684 kA/m. The melting temperature (T) remarkably decreases by the addition of Zr and B, e.g., from 1837 K for FePt to 1345 K for (Fe0.55Pt0.45)(78)Zr4B18. The Ll(0) phase with Zr and B directly formed by the rapidly quenching shows high thermal stability and maintains up to T,,. The simultaneous addition of Zr and B facilitates the direct formation of the ordered Ll(0) phase with a grain size of 20-200 nm by rapidly quenching the melt through the effect of the decreasing Tm and the increasing the stability of the Ll(0) phase by the solution of Zr and B into the phase. The substitution of Fe by Co monotonously decreases T,, from 1345 K of (Fe0.5Pt0.50)(78)Zr4B18 to 1083 K Of (Co0.5Pt0.50)(78)Zr4B18. However, H, drastically decreases from 684 kA/m of (Fe0.50Pt0.50)(78)Zr4B18 to 12 kA/m Of (COO. Pt-50(0.50))(78)Zr4B18, which has a single fcc structure in an as-quenched state. The decrease in Hc with increasing Co content up to Fe:Co = 1:3 is caused by the decreasing of the magnetocrystalline anisotropy, which originates from the decreasing the long-range order parameter of the Ll(0) phase. (c) 2007 Elsevier B.V. All rights reserved.