Effect of ${\rm H}_{2}$ on the Formation Mechanism and Magnetic Properties of FePt Nanocrystals

A variety of differently shaped FePt nanocrystals, including flower-like FePt-Fe₃O₄ nanodendrites, flower-like FePt nanodentrites, mixtures of worm-like nanowires and nanoparticles and spherical nanoparticles were synthesized by properly choosing shielding atmosphere including pure Ar, mixture of different ratio of Ar and H₂, and pure H₂. The growth of FePt nanocrystals in the presence of H₂ is mainly owing to H₂ absorbed on the surface of seeds, which hindered the seeds of the particles´ aggregation and promoted the growth on the surface of the seeds. The as-synthesized nanocrystals were found to be superparamagnetic at room temperature and their ferromagnetic-superparamagnetic transition temperature was 100 K, 55 K, 25 K and 20 K respectively, which was correlated to their composition and morphology.