Synthesis of self-assembled monodisperse 3 nm FePd nanoparticles: Phase transition, magnetic study, and surface effect

Self-assembled monodisperse 3 nm face centered cubic (fcc) FePd particles are synthesized by modified polyol method using polyethylene glycol-600 as a reducing agent and oleic acid and oleyl amine as surfactants. As-synthesized FePd nanoparticles are superparamagnetic at room temperature and ferromagnetic below blocking temperature (T-B=21 K). The significant enhancement in saturation magnetization is observed at 5 K. This is attributed to surface effect for 3 nm size particles. The nanoparticles are spherical with uniform dispersion as depicted in transmission electron microscopy study. The noninteracting behavior of as-synthesized FePd nanoparticles is verified through Langevin fit. The saturation magnetization (sigma(s)) and mean moment of (mu(m)) particles are computed to be sigma(s)=22.73 emu/g and mu(m)=4466 mu(B), respectively. The ordered face centered tetragonal (fct) phase of composition Fe43Pd57 was obtained from disordered fcc FePd phase by annealing at 550 degrees C for 1 h under reducing atmosphere of (N-2+H-2) gas. The hard magnetic fct Fe43Pd57 phase exhibits high coercivity H-c=1180 Oe, saturation magnetization sigma(s)=65.2 emu/g, and hysteresis loop area of 1.5x10(6) erg/cm(3) at 300 K.