X-ray absorption and diffraction studies of thin polymer/FePt nanoparticle assemblies

We have produced assemblies of monodisperse 4 nm FePt nanoparticles using polymer-mediated layer-by-layer deposition at room temperature. The process leads to good control of particle assembly thickness and offers great potential for future fabrication of ultra-high density magnetic storage media. Vibrating sample magnetometry with fields up to 9 T was applied to study the magnetic properties of the particle assemblies as a function of annealing condition while near edge x-ray absorption fine structure (NEXAFS) spectroscopy and x-ray diffraction (XRD) were used to investigate the chemical nature and structural properties within particles. It was found that the coercivity can be as high as 22.7 kOe for samples annealed at 800 degreesC, the moment density (normalized to the particle volume) for the sample annealed at 650 degreesC is estimated close to the value for bulk FePt, at 1140 emu/cm3. NEXAFS spectroscopy shows that the Fe in the as-deposited assemblies is partly oxidized, and the oxidation is greatly reduced by annealing. XRD studies on the assemblies annealed at high temperature revealed the increased atomic order and the formation of the high-anisotropy L1(0) phase within the particles. However, the high-temperature annealing also resulted in nanoparticle agglomeration. (C) 2003 American Institute of Physics.