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

The ordered L10-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 (Hc) higher than 200 kA/m in an as-quenched state. In particular, the melt-spun (Fe0.50Pt0.50)78Zr4B18 alloy exhibits high Hc of 684 kA/m. The melting temperature (Tm) remarkably decreases by the addition of Zr and B, e.g., from 1837 K for FePt to 1345 K for (Fe0.55Pt0.45)78Zr4B18. The L10 phase with Zr and B directly formed by the rapidly quenching shows high thermal stability and maintains up to Tm. The simultaneous addition of Zr and B facilitates the direct formation of the ordered L10 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 L10 phase by the solution of Zr and B into the phase. The substitution of Fe by Co monotonously decreases Tm from 1345 K of (Fe0.50Pt0.50)78Zr4B18 to 1083 K of (Co0.50Pt0.50)78Zr4B18. However, Hc drastically decreases from 684 kA/m of (Fe0.50Pt0.50)78Zr4B18 to 12 kA/m of (Co0.50Pt0.50)78Zr4B18, 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 L10 phase.