The structure and the coercivity (Hc) of the rapidly quenched (Fe0.55Pt0.45)bal.Zr0-8B 0-24 alloys prepared by the melt-spinning technique have been investigated. 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 Hc greater than 200 kA/m in an as-quenched state. In particular, the melt-spun (Fe 0.55Pt0.45)78Zr2B20 and (Fe0.55Pt0.45)78Zr4B18 alloys exhibit high Hc of 341 kA/m and 649kA/m, respectively. The melting temperature (Tm) remarkably decreases by the addition of Zr and B, e.g., from 1833 K for Fe0.55Pt0.45 to 1360 K for (Fe0.55Pt0.45)78Zr4B18. The L10 phase, which is directly formed by the rapidly quenching method, is considered to include Zr and B, shows high thermal stability and maintains up to Tm. On the other hand, the (Fe0.55Pt 0.45)77-85Zr0-8B15-22 alloys, produced by the Cu-mold casting with a lower cooling rate than the melt-spinning technique are found to comprise of mixed structures of L10-FePt and some compound phases such as ZrB12, PtZr, Fe3B, and FeB, and the alloys have a Hc of 40-100 kA/m, which is lower than that of the melt-spun alloys. Apart from the L10 phase, the other phases such as ZrB12, PtZr, Fe3B, and FeB are suppressed and the L10 phase containing Zr and B elements is formed by rapidly quenching the alloy melt with low Tm. The simultaneous addition of Zr and B facilitates the direct formation of the ordered L10 phase with a grain size of 20-200nm 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.
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