Abstract
Abstract Control of ordering temperature and crystalline orientation in FePt films and nanostructures This dissertation focuses on the low-temperature ordering of (001)-oriented L10 FePt films and nanostructures. Three main topics are discussed. The first one is reducing the ordering temperature. FePt films with a coercivity of as high as 7700 Oe were obtained by forming-gas (Ar 95% + H2 5%) annealing at 275 ℃. Hydrogen atoms may occupy the interstitial sites of FePt, inducing a local strain or an agitation which accelerates the ordering of FePt. The coercivity increased with the number of hydrogen atoms dissolved in the FePt lattices. The second topic is the fabrication of (001)-orientated FePt films at low temperature, by subsequently annealing FePt films deposited on Cr65Mo15Mn20 underlayers in forming-gas atmosphere. Fe and Pt intermediate layers were used to adjust the strain energy and the orientation of FePt. Samples annealed at 275 ℃ with thin Pt layers (< 5 nm) have relatively small coercivity because of the stabilizing effect of the underlayers. The other means of attaining a (001)-orientated FePt films at low temperature is the annealing of an atomic-scale Fe/Pt multilayers (MLs). A highly ordered L10 FePt phase can be obtained by annealing at 400 ℃ for 2 s. The very short annealing time and relatively low annealing temperature demonstrate the alternate depositions of atomic-scale Fe and Pt MLs can reduce the diffusion length of FePt into the L10 lattice of FePt. In the γ2-FePt phase, the atomic arrangement of Fe and Pt in the [001] direction is like that of atomic-scale Fe/Pt MLs. Therefore, (001)-orientated FePt films can be acquired by annealing atomic-scale Fe/Pt MLs The last topic in this dissertation is control of the nanostructure of the ordered L10 FePt phase. L10 granular FePt-SiO2 films with a (001) preferred orientation and well-separated grains of 5.14 ± 0.75 nm were also obtained by depositing atomic-scale Fe/Pt/SiO2 MLs on glass substrates and subsequently annealing MLs at a temperature of 350 ℃. Further increasing the annealing temperature resulted in the formation of nano-particles. Two kinetic processes were taking place during the post-annealing of a disordered FePt film. One is the ordering of the L10 FePt phase; the other is agglomeration. Inserting ultra-thin SiO2 layers into atomic-scale [Fe/Pt]n MLs cannot effectively accelerate the ordering process but improve agglomeration.