Crystallographic ordering studies of FePt nanoparticles by HREM

FePt nanoparticles with a size of 4 nm were prepared by the polyol process according to the reaction route described by Sun et al. The particles were annealed at 550 C and 580 C for 30min in N2 atmosphere, developing coercivities of up to 8.8 kOe. From conventional transmission electron microscopy the coherence lengths of the self-assembly were found to be as large as 10mm in the as-prepared state and about 1 mm in the annealed state. The degree of sintering is zero for the 550 C annealed samples and only a small amount for the 580 C annealed samples. Ordering of the asprepared fcc structure of the FePt nanoparticles into the L10 structure as a result of annealing is studied by highresolution electron microscopy. In this investigation monodispersed nanoparticles are frequently found to undergo partial chemical ordering to the hard magnetic L10 phase without a change in size. Qualitative HREM observations about the amount of ordering of monodispersed nanoparticles, the low degree of sintering of the samples and large coherence length of the self-assembly together with the high coercivity developed upon annealing suggest the potential production of self-assembled ferromagnetic FePt arrays in future high-density magnetic data storage. r 2003 Elsevier B.V. All rights reserved.