Direct synthesis of Pt based L10 structured nanoparticles (invited) -: art. no. 10J307

Equiatomic FePt and CoPt nanoparticles with the ordered L1(0) structure are attractive as ultrahigh density magnetic recording media. In a recent work, chemically synthesized fcc-FePt nanoparticles with narrow size distribution and their self-assembled array with close-packed microstructure has been achieved successfully. However, the particles coalesced during the subsequent annealing step necessary to obtain L1(0) FePt nanoparticles. In the present study, we have successfully demonstrated the direct synthesis of L1(0) FePt nanoparticles at low temperature of 553 K using the "modified polyol method" without subsequent annealing, whose diameter is 5-10 nm and intrinsic magnetocrystalline anisotropy field (H-k) is 31 kOe. This indicates that precisely controlling the reaction kinetics, especially low reduction rate through optimizing the polyol/Pt mole ratio and type of polyol are very important for directly synthesizing the L1(0) FePt nanoparticles. Furthermore, we investigated the size, morphology and composition dependence of the magnetic properties of FePt nanoparticles in order to clarify the L1(0) ordering mechanism. As a result, clear evidence of the existence of the critical diameter for the thermodynamical L1(0) ordering is not observed in the size range above 2 nm. Furthermore, the recrystallization and sintering process can be a driving force for promoting the L1(0) ordering, and hence, Fe and Pt atom diffusion at the grain boundary plays an important role to the L1(0) ordering of FePt nanoparticles. (c) 2005 American Institute of Physics.