Structures And Properties Investigation Of L1₀-FePt

Because of its ultra-high magnetocrystalline anisotropy Ku, L1₀-FePt has great application potential for future ultra-high density perpendicular magnetic recording media. In this thesis we have combined the thin film technique with high resolution electron microscopy, investigating the structure control of the L1₀-FePt thin film, the relationship between growth conditions and the magnetic properties and the ordering state of small FePt nanoparticle. We have also tried to develop electron energy-loss spectroscopy based method to investigate the magnetic linear dichroism of L1₀-FePt.In pursuance of high density perpendicular recording, we have investigated the influence of the fabricating conditions on the degree of [001] perpendicular orientation of Pt/Fe multilayer grown on amorphous substrate. It was found that the annealing temperature and the annealing time did not have much effect on the degree of [001] perpendicular orientation, while this [001] perpendicular orientation degree can be promoted partly when decrease the growth rate of the Fe layer at elevated temperature. Perfect [001] perpendicular oriented L1₀-FePt thin film was fabricated epitaxially on MgO substrate and the magnetic properties were investigated as a function of the growth conditions. In order to solve the high coercivity problem associated with its high magnetocrystalline anisotropy in L1₀-FePt, Pt/Fe multilayer was rapid thermally annealed while oxidation was introduced to fabricate exchange-coupled Fe₃O₄/L1₀-FePt bilayer. Micromagnetic simulation results indicate that the thickness of the Fe₃O₄ layer should smaller than a critical value which is about 10 nm. The introduction of the Fe₃O₄ layer can reduce the coercivity of L1₀-FePt by about 28.6%.The magnetic properties of L1₀-FePt depend strongly on the degree of chemical ordering. The ordering state of a single FePt decahedron nanoparticle was studied using aberration-corrected high resolution transmission electron microscopy (HRTEM). The HRTEM image of this particle indicate that the integrated intensity of the {002} layer atoms oscillated periodically from one shell to another for the inner five {002} shells while the outer three {002} shells did not show this kind of oscillation. Multislice image simulation results indicate that this intensity oscillation cannot be found in the images of disordered FePt decahedrons. The experimental decahedron may be ordered for the inner five {002} shells and the ordering state for the outer three shells remains unknown. Our results show that FePt particle, as small as 3.4 nm, can still be ordered. Even though, multiple twinning causes an effective reduction of the magnetic anisotropy.We have employed electron energy-loss spectroscopy to study the FePt related materials. Using energy-loss spectroscopic profiling (ELSP) technique, we obtained the chemical shift information for Fe-L edge. Combined with oxygen elemental mapping results, it was proposed that oxygen diffused into the L1₀-FePt layer to form oxidation precursor along the grain boundary. We have also combined the ELSP method with multivariate statistical analysis (MSA) method to develop a method of experimentally measuring the dichroic signals in an anisotropic material. It was tested on the C-K ELSP images from a single multi-wall carbon nanotube and the intrinsic averaged spectrum and the dichroic spectrum were successfully recovered from MSA processing. We used this ELSP-MSA technique to investigate the magnetic anisotropy of a single L1₀-FePt particle Fe-L edge image. The dichroic like signal was recovered which was due to its magnetic anisotropy. This kind of magnetic linear dichroism can be used to study the magnetic moment of magnetic materials.