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 (Fe 0.50 Pt 0.50 ) 78 Zr 4 B 18 alloy exhibits high H c of 684 kA/m. The melting temperature (T m ) remarkably decreases by the addition of Zr and B, e.g., from 1837 K for FePt to 1345 K for (Feo.55Pto.45) 78 Zr 4 B 18 . The Ll 0 phase with Zr and B directly formed by the rapidly quenching shows high thermal stability and maintains up to T m . 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 T m 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 m from 1345 K of (Fe 0.50 Pt 0.50 ) 78 Zr 4 B 18 to 1083 K of (Co 0.50 Pt 0.50 ) 78 Zr 4 B 18 . However, H c drastically decreases from 684 kA/m of (Fe 0.50 Pt 0.50 ) 78 Zr 4 B 18 to 12 kA/m of (Co 0.50 Pt 0.50 ) 78 Zr 4 B 18 , which has a single fcc structure in an as-quenched state. The decrease in H c 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 Llo phase.