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 550 °C transformed the particles from the fcc to the L10 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 (Hc>5000 Oe) and a soft component (Hc<2000 Oe). 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 L10 phase.