One-step Preparation Of Fct-structure FePt Nanoparticles By Doping Cu And Research On Its Phase Transition

At low temperature (<300℃), the synthesis of FePt nanoparticle is commonly face-centered cubic (FCC) structure, this structure does not have high magnetocrystalline anisotropy. High temperature annealing can cause FePt structural transformations from the fcc structure to the fct structure, but it also can make nanoparticles gather together and grow up. Doping FePt nanoparticle is a practical way, the introduction of other elements, without high temperature annealing treatment, to synthetise directly high magnetic FePt nanoparticles with fct structure at one-step.Partially ordered (FePt)1-x Cux nanoparticles (NPs) were directly prepared by doping copper additive to FePt NPs without post-thermal annealing. The experiment were conducted by the simultaneous decomposition of iron acetylacetonate and reduction of platinum acetylacetonate and copper acetylacetonate. The chemical, Hexadecylamine, was used as a high boiling point solvent,1,2-hexadecanediol was used as a stabilizer, oleic acid and oleylamine was used as a surfactant. A nonmagnetic mechanical stirrer was used in order to avoid agglomeration of the fctstructured FePt NPs during synthesis. Using X-ray diffractometer (XRD), vibrating sample magnetometer (VSM), transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray energy spectrum analysis (EDS) and other test methods to conduct morphology structure and performance characterization of the samples, and illustrating the mechanism that the doping elements promote FePt phase transformation from fcc into fct structure. Specific content is as follows:(1) Fixed iron and platinum reaction precursors ratio of1:1, the effects of copper additive on the morphology, structure and chemical ordering of as-prepared FePt NPs were investigated. X ray diffraction results showed that without Cu doping the as-prepared NPs possessed cc structure and gradually showed typical fct diffraction peaks after increasing the Cu doping concentration. Meanwhile the metallic Cu phase is observed. TEM images exhibited that as-prepared NPs had bigger particles size and wider particle size distribution after introducing Cu additive. Magnetic properties measurement showed that a coercivity of1300Oe was obtained when the molar ratio of Cu reached25.9%in the (FePt)1-xCux nanoparticles. This study indicated Cu doping has a certain in promoting the phase-transition of FePt nanoparticles, and Phase transition temperature is340℃.(2) the change of the content of Fe and Pt effecting on the properties of synthetic FePtCu nanoparticles is explored. The results show that when Fe:Pt=1:1in the reaction precursors, being the optimum mole ratio, the synthesis of FePt magnetic nanoparticle can be the best.(3) Using different solvents (tetraethylene glycol, dibenzyl ether), different surface modification agent polyvinylpyrrolidone (PVP) to research the effect on the properties of synthetic FePt nanoparticles by Cu doping. Results show that using PVP also can promote the synthesis of FePt nanoparticles with fct structure; When using tetraethylene glycol and dibenzyl ether as solvent, do not fail to effectively promote FePt phase transition.(4) Mn(acac)2is studied on synthesis of FePt nanoparticles whether it have positive influence. Results showed that doping Mn elements failed to effectively promote FePt nanoparticle phase transition.Comprehensive above, we can conclude that when iron platinum mole ratio of1:1in the precursors and the solvent for Hexadecylamine, adding Cu to FePt also could promote phase transformation from the fcc to the fct phase.