X-ray absorption and diffraction studies

We have produced assemblies of FePt nanoparticles using high temperature solution phase synthesis and polymer-mediated layer-by-layer deposition allowing precise control of the particle self-assembly. The as-deposited particles have a narrow size distribution offering the potential for use as ultra-high density magnetic storage media and ultimately storage of one bit per individual nanoparticle. Vibrating sample magnetometry was applied to measure the magnetic properties of the particle assemblies as a function of anneal 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. It was found that the coercivity can be as high as 22.7 kOe for samples annealed at 800°C, the moment density (normalized to the particle volume) has a maximum of 1140 emu/cm for annealing at 650°C equal to the value for bulk FePt. NEXAFS spectroscopy shows that the Fe in the as-deposited assemblies is partly oxidized, and the oxidation is greatly reduced by annealing. XRD indicates an increased formation of the chemically ordered, high anisotropy L10 phase and the onset of nanoparticle agglomeration for annealing at higher temperatures. SLAC-PUB-9989 June 2003