X-ray scattering and absorption spectroscopy study of FePt nanoparticles

• Main Authors: Tzu-Wen Huang, 黃子文
• Other Authors: Chih-Hao Lee
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/05899622302192664672

博士 === 國立清華大學 === 工程與系統科學系 === 95 === In this thesis the phase and magnetic transition of 3-5 nm FePt nanoparticles surface and monolayer system were studied using X-ray scattering and absorption techniques. A self-assembled structure was verified as a face center cubic packing structure by grazing incident X-ray diffraction. However, this self-assembled structure was easily destroyed when the surfactant on the particles surface were decomposed at the annealing temperatures more than 400 oC. Besides, the grain sizes also didn’t change enormously, even at the temperature up to 640 oC. The remaining carbons which burned out from the surfactant were investigated by X-ray absorption spectroscopy. The evidence shows that those remaining heterogeneous materials, such as carbon or silicon, on the particles surface might be useful to preventing aggregation during the post-annealing. In order to keep those particles intact during the annealing, we also use a layer of non-magnetic material, gold, as an overlayer material coating on FePt monolayer particles. Unfortunately, due to the high electron density of Au on the surface, it is difficult to define the particles sizes and distribution by the traditional X-ray scattering during the annealing process. Thus, the anomalous grazing incident small angle x-ray scattering (anomalous GISAXS) has been developed successfully to measure the morphology of FePt monolayer with Au overlayer system. Based on the anomalous GISAXS results, we proved that the Au is an effectively cover layer to prevent those FePt nanoparticles from collapsing together even at the annealing temperatures up to 800 oC for 1 h. In addition, by measuring the diffraction anomalous fine structure spectrum in the near edge region, the ordering FePt L10 phase was observed. According to this approach, the particle size of monolayer FePt nanoparticles can remain small to fit the ultrahigh density demand for the next generation magnetic disk.