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Abstract:
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Fabrication of chemically disordered FePt particles ranging from 2 - 9 nm with a precision of 1 nm has been achieved through modification of key process variables including surfactant concentration , heating rates and the type of iron precursor . In addition , the shape evolution of the FePt nanoparticles during particle growth can be manipulated to give cubic or rod geometries through changes to the surfactant injection sequence and solvent system . The primary method for synthesis of the disordered FePt nanoparticles is the polyol reduction reported by Fievet et al . , which has been modified and used extensively for synthesis of diff ering nanoparticle systems . Our procedures use platinum acetylacetonate , iron pentacarbonyl or ferric acetylacetonate as precursors for the FePt alloy , oleic acid and oleyl amine for the surfactants , 1 ,2 -hexadecanediol to assist with the reduction of the precursors and either dioctyl ether or phenyl ether for the solvent system . For iron pentacarbonyl based reactions , adjustment of heating rates to reflux temperatures from 1 - 15 oC per minute allows control of FePt particle diameters from 3 - 8 nm . Substitution of iron pentacarbonyl with ferric acetylacetonate as the iron source results in 2 nm particles . A high platinum to surfactant ratio of 10 to 1 will yield 9 nm FePt particles when iron pentacarbonyl is used as the precursor . For use of these particles in advanced applications , the synthesized particles must be transformed to the L1o phase through annealing at temperatures above 500oC . Inhibition of particle sintering can be avoided through dispersion in a NaCl matrix at a weight ratio of 400 to 1 salt to fcc FePt particles . Production of L1o FePt nanoparticles with high magnetic anisotropy with this process has been successful , allowing the original size and size distribution of the particles . |