Low-temperature ordering of FePt nanoparticles by alternate reduction of metal salts in aqueous medium

• FePt nanoparticles were synthesized by the alternate reduction of chloroplatinic acid and ferric chloride.
• The synthesized temperature is 70 °C.
• XRD and selected area electron diffraction show the initiation of phase transition from chemically disordered face center cubic to ordered face center tetragonal at 400 °C.
• The magnetic measurements at room temperature show a double phase hysteresis loop at 400 °C, with the coercivity of about 3.4 kOe.

FePt nanoparticles have been successfully synthesized by the alternate reduction of chloroplatinic acid and ferric chloride, in the presence of acetyl trimethyl ammonium bromide as a surfactant in aqueous medium. Detailed investigations on the structural and magnetic properties of these nanoparticles were presented as a function of annealing temperature. Selected area electron diffraction shows the initiation of phase transition from the as-synthsized phase to ordered face center tetragonal (FCT) at 400 °C. The x-ray diffraction and magnetic measurements confirm the transformation to FCT phase at 400 °C. The magnetic measurements at room temperature show a double phase hysteresis loop at 400 °C and a nearly single phase hysteresis loop at 600 °C, with the coercivity of about 3.4 kOe and 16.2 kOe, respectively. We report for the first time this alternate reduction method in synthesizing FePt nanoparticles, obtained a decrease of about 100 °C in the ordering temperature.