Synthesis, chemical ordering, and magnetic properties of FePtCu nanoparticle films

FePtCu nanoparticles with varying composition were prepared by the simultaneous polyol reduction of platinum acetylacetonate and copper bis(2,2,6,6-tetramethyl-3,5-heptanedionate) and the thermal decomposition of iron pentacarbonyl. As prepared the particles had a fcc structure with an average diameter of 3.5 nm and were superparamagnetic. Heat treatment of the self-assembled films at temperatures above $\text{550\hspace{0.05em}°}\mathrm{C}$ transformed the particles from the fcc to the ${\text{L1}}_0$ phase, give in-plane coercivities as high as 9000 Oe. X-ray diffraction revealed that the Cu remained in the films and the presence of an extra peak, indicating a second phase was present. Consistent with two or more phases, the magnetic hysteresis curves could be decomposed into a hard component ${\mathrm{(H}}_c\text{>5000\hspace{0.17em}}\mathrm{Oe})$ and a soft component ${\mathrm{(H}}_c\text{<2000\hspace{0.17em}}\mathrm{Oe}\mathrm{).}$ Unlike our earlier results for Ag in FePt, adding Cu to FePt did not lower the temperature required for phase transformation from the fcc to the ${\text{L1}}_0$ phase.