Preparation And Characterization Of FePt Nanostructures And FePt-Inorganic Matrix Composite Systems

With the rapid development of information technology, the storage of information is more and more important. As one of the main methods of memories, the magnetic recording technique keeps improving continuously. The traditional magnetic recording media such as CoPtCr cannot meet the requirements of ultra-high density magnetic storage due to the limitation of superparamagnetic effect. The new materials such as FePt/CoPt alloy with L1O phase have attracted great attention because of its ultra-high magnetic anisotropy energy, good chemical and thermal stability.In this paper, iron pentacarbonyl and platinum acetylacetonate were used to synthesize different FePt nanostructures by a solution method. At the same time, in order to circumvent the problem of FePt particle coalescence during high temperature annealing for the L1O ordering, several FePt nanoparticle/inorganic matrix composite systems have been fabricated to protect the FePt nanoparticle. The structure, morphology and magnetic performance were also characterized deeply.The main achievements are summarized as follows:1. FePt nanoparticles were synthesized by a solution method. The optimal processing conditions were obtained by changing the reaction temperature and initial Fe: Pt molar ratio. When the initial proportion of Fe-Pt is 2:1 and the reaction temperature is 220℃, the FePt nanoparticles show better dispersion with size of about 4nm. After annealed at 700℃, the FePt particles exhibit better magnetic performance with degree of order S of 0.96 and coercive of above 7000Oe, but the FePt particles also display serious aggregation phenomenon.2. The FePt nanowires were synthesized at 180℃using solvents of Oleylamine and hexadecane successfully. The length of FePt nanowires can be varied from 40nm to 100nm by controlling the molar proportion of Oleylamine and hexadecane. The structure and composition of FePt nanowires were characterized by HRTEM and EDS. The Fe-Pt proportion is 0.54:0.46. Due to the incomplete L1O phase transition, FePt nanowires contain considerable fcc-soft magnetic phase, the coercive of FePt nanowires is very small.3. In order to prevent from FePt nanoparticles' coalescence, FePt-MgO, FePt-TiO2 and FePt-SiO2 composite systems have been fabricated by means of sol-gel method. After annealed at 700℃for 1 hour, the inorganic martrix can protect FePt nanoparticle effectively. The composite systems show evidently improved dispersion and magnetic performance, however the degree of order S decreases from 0.96 to 0.6~0.8. It is found that the FePt concentration and pH value has great effect on magnetic properties.For FePt-MgO system, when the pH=7 and Fe:Pt ratio composite is 1:2, a relatively saturation hysteresis loop was obtained with squareness of 64.4% and the coercive force is 4664 Oe. For FePt-TiO2 system, when the pH of TiO2 is 5.5 and the composite ratio is 1:2, we can get a system similar to FePt-MgO system in dispersion and magnetic performance (Hc=4436 Oe). For FePtSiO2 system,3300 Oe is confirmed and a further study is needed.