Formation and magnetic properties of Fe–Pt alloy clusters by plasma-gas condensation

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Abstract
Size-monodispersed FexPt1−x alloy clusters were synthesized using a plasma-gas-condensation technique which employs two separate elemental sputtering sources and a growth chamber. The composition of the alloy clusters was controlled by adjusting the ratio of the applied sputtering power. We found that high-temperature disordered fcc–FexPt1−x clusters whose mean diameters of 6–9 nm depend on the Ar gas flow ratio were formed for a wide average composition range (x≈0.3–0.7), and the lattice constant of as-doposited clusters increases almost linearly with decreasing x, being extrapolated to the value of pure Pt metal. For Fe49Pt51 cluster-assembled films, high coercivity (8.8 kOe) was obtained by annealing at 600 °C within 10 min due to improved chemical ordering, although as-deposited cluster-assembled films have lower blocking temperatures than room temperature, and show a small coercivity value (∼25 Oe) at room temperature due to intercluster magnetic interaction.