Compositional Evolution of FePt Nanoparticles Prepared by Different Organometallic Synthesis Routes
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1032-I10-13
Compositional Evolution of FePt Nanoparticles Prepared by Different Organometallic Synthesis Routes Chandan Srivastava, and Gregory B Thompson Department of Metallurgical and Materials Engineering, The University of Alabama, Tuscaloosa, AL, 35487 ABSTRACT Self-assembled FePt nanoparticle arrays are candidate structures for ultrahigh density magnetic storage media. One of the factors limiting their application to this technology is particle-to-particle compositional variation. In the present study, an analysis is provided for the formation mechanism of FePt nanoparticles synthesized from the thermal decomposition of Fe(CO)5 and the reduction of FeCl2 by superhydride. In both processes, Pt rich seeds initially form from the reduction of Pt acetylacetonate. The particle formation mechanism has been studied by extracting particles at different stages of the synthesis and individually determining particle-to-particle composition by STEM-XEDS. In the case Fe(CO)5, the Fe is gradually incorporated into the Pt seeds and produces a wide variation in compositional distribution about the mean value. In contrast, the FeCl2 has a nearly instantaneous shift in composition to the average value with the introduction of the superhydride reducing agent. The discrepancies in compositional uniformity between the two processes will be discussed in terms of the intrinsic differences between the different precursors. INTRODUCTION Self-assembled FePt arrays are considered as candidate material structures for next generation magnetic recording technology1. One major challenge towards the application of these nanoparticles is controlling the particle-to-particle composition and size uniformity. Yu et. al.2 have reported that FePt nanoparticles produced by the simultaneous decomposition of Fe(CO)5 and the reduction of Pt(acac)2 in phenyl ether solvent produces nanoparticle dispersions with wide particle-to-particle compositional distributions. This distribution indicates that only a fraction of nanoparticles have the favored equi-atomic stoichiometry. This variation in the quantitative ratio of elemental constituents can produce a variation in the structural and magnetic properties from particle-to-particle. Saita et al.3 have suggested that this large variation in composition, as seen by Yu et al.2, is because of the inhomogenity in the slow decomposition of Fe(CO)5 during the synthesis reaction. This suggests that that the wide compositional distribution is dependent on the type of precursors used during the synthesis. This proceeding paper reports the particle-to-particle composition distributions prepared by two different synthetic routes involving different Fe precursors. The compositional evolution of the particles was analyzed during the process by extracting the particle dispersions at different stages of the synthesis. EXPERIMENTAL PROCEDURE To investigate and compare the composition distribution in FePt nanoparticles as a function of the synthesis procedure, particles were synthesized by two widely used processes: the i
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