Direct synthesis of Pt based L1 structured nanoparticles (invited)

Abstract

Equiatomic FePt and CoPt nanoparticles with the ordered L10 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 L10 FePt nanoparticles. In the present study, we have successfully demonstrated the direct synthesis of L10 FePt nanoparticles at low temperature of 553K using the “modified polyol method” without subsequent annealing, whose diameter is 5–10nm and intrinsic magnetocrystalline anisotropy field (Hk) is 31kOe. 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 L10 FePt nanoparticles. Furthermore, we investigated the size, morphology and composition dependence of the magnetic properties of FePt nanoparticles in order to clarify the L10 ordering mechanism. As a result, clear evidence of the existence of the critical diameter for the thermodynamical L10 ordering is not observed in the size range above 2nm. Furthermore, the recrystallization and sintering process can be a driving force for promoting the L10 ordering, and hence, Fe and Pt atom diffusion at the grain boundary plays an important role to the L10 ordering of FePt nanoparticles.