Direct synthesis of Pt based L1 structured nanoparticles (invited)

Abstract

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.

A Micellar Approach to Magnetic Ultrahigh‐Density Data‐Storage Media: Extending the Limits of Current Colloidal Methods

“…[10,14] However, even in these cases, the particles still need to be encapsulated with an organic-ligand shell, either after deposition from a cluster beam [12] or during synthesis, to guarantee their ordered organization. Typical interparticle spacings are thus the same as described before, resulting in dipolar coupling and, additionally, the particle-ligand interactions can deteriorate the magnetic properties.…”

Thermal treatment effects in the self-assembly of FePt nanoparticle arrays

“…The d-spacing values of (111) planes at 0.221 nm and (11 0) planes at 0.272 nm verify that despite the non-equiatomic average Fe-Pt ratio, a partial disordered-to-ordered structure transition actually occurred using dioctylether as a solvent [19]. The formation of fct-FePt nanoparticles may be associated not only with the chemical composition fluctuations, as described, but also with the particle size dependence of the fcc-fct phase transition [20,21]. An additional confirmation is the existence of the characteristic, for ordered FePt alloys, (0 0 1) planes at 0.373 nm (Fig.…”

Microstructure and magnetic properties of L1-FePt thin films prepared under high pressures

“…This ordering transition is dominantly governed by the growth of L1 0 ordered domains [6][7][8] and thus inevitably leads to large grain sizes ͑e.g., d = 30-50 nm͒ and a relatively wide size distribution. [9][10][11] Although various approaches, e.g., element doping, applying underlayer and toplayer have been successfully employed to reduce the grain size of L1 0 -FePt thin films, 5,12-14 these techniques are incapable of improving the size uniformity and even result in a significant decrease in the ordering degree. Obviously, to produce a microstructure with an ultrafine grain size and a narrow size distribution for the L1 0 -FePt thin films, the nucleation rate of the L1 0 ordered domains should be enhanced, while the growth rate of the FePt grains should be inhibited during the ordering phase transition.…”