Synthesis of L1₀-(Fe_yPt_100-y) _100-xCu_x nanoparticles with high coercivity by annealing at 400 °C

(Fe_yPt_100-y)_100-xCu_x nanoparticles with various compositions were synthesized by the simultaneous polyol reduction of Pt(acac)₂ and Cu(acac)₂ and the thermal decomposition of Fe(CO)₅. The as-made particles had a disordered fee structure and an average diameter of ∼4.8 nm. The result of x-ray diffraction indicated a transformation from fee structure to fct structure in some samples after annealing at 400 °C for 1 h, and the c/a ratio of lattice constant decreased with increasing Cu content. The doping of Cu clearly plays a significant role on the reduction of the ordering temperature in the ternary (Fe_yPt_100-y)_100-xCU_x alloy. In addition, the ordering of (Fe_yPt_100-y) _100-xCu_x nanoparticles is significantly dependent on the composition of Fe and Pt. As a result, (Fe₄₇Pt₅₃) ₇₄Cu₂₆ nanoparticles have the coercive fields of ∼10 and ∼2 kOe at 10 K and room temperature, respectively.