降低自组装FePt薄膜有序化温度的研究

【作者】 彭印；

【导师】 贺淑莉；

【作者基本信息】 首都师范大学 ， 材料物理与化学， 2008， 硕士

【摘要】 本文利用高温液相法直接合成出了尺寸为7nm具有立方形状的FePt纳米颗粒和具有core/shell结构的Fe₃₀Pt₇₀/Fe₃O₄纳米颗粒,并用分子中介自组装的方法制备了自组装薄膜。利用透射电子显微镜（TEM）、X射线衍射仪（XRD）和振动样品磁强计（VSM）分别对粒子的形貌、微结构、物相组成和磁性进行了研究。7nm立方形状的FePt纳米颗粒自组装的薄膜在500 oC～650 oC温度下退火后,XRD结果表明FePt在500oC开始由无序的fcc结构转变为有序的fct结构转变,且样品的有序度S随着退火温度的上升而增加;当退火温度为570oC时,样品的有序度达到了0.88,表明7nmFePt颗粒的有序化温度明显低于文献中报道的3-4nmFePt颗粒的有序化温度。这表明通过制备较大尺寸的FePt颗粒可以有效地降低有序化转变温度。Fe₃₀Pt₇₀/Fe₃O₄ core/shell纳米颗粒自组装的薄膜在70%Ar +30%H2的混合气氛下进行退火,退火温度是350 oC～650 oC。微结构分析表明样品350oC退火后,shell中的Fe3O4被还原成Fe;400 oC以上温度退火时shell中的Fe与core中的Fe30Pt70扩散成一体,并形成L10有序结构的FePt颗粒。在Fe₃₀Pt₇₀/Fe₃O₄ core/shell纳米颗粒退火过程中,Fe原子向FePt的扩散促进了Fe原子和Pt原子的重新排列,有利于L10相的形成。构建core/shell结构是显著降低FePt纳米颗粒有序化温度的一条新的有效途径。更多还原

【Abstract】 7nm FePt nanoparticles with cubic shape and Fe₃₀Pt₇₀/Fe₃O₄ core/shell nanoparticles were synthesized by high temperature solution phase method. The transmission electron microscopy （TEM）, X-ray diffraction system （XRD） and vibrating sample magnetometer （VSM） were used to characterize the particle size,microcrystal structure and magnetic property.The post annealing of 7nm FePt nanoparticles with cubic shape have been performed at the temperatures from 500 to 650°C for 60min. X-ray diffraction results showed that the chemical ordered （fct） FePt phase was formed in the sample annealed at 500oC for 1 hour. The ordering parameter increased with increasing annealing temperature. S of the assembly annealed at 570°C almost reaches 0.88. It is much higher than that of 3-4nm FePt nanoparticles. It can be summarized that the ordering temperature can be reduced by the synthesis of large size FePt nanoparticles.The post annealing of Fe₃₀Pt₇₀/Fe₃O₄ core/shell nanoparticles have been performed at the temperatures from 350 to 650°C for 60min.After annealing under a flow of forming gas （70%Ar2+30%H2） for 1h at 350°C, the iron oxide shell was reduce to Fe. When the annealing temperature above 400°C, the Fe atom in the shell diffuse to Pt-rich core, which leaded to the formation of L10 FePt. It is benefit for the forming of L10 phase that annealing Fe₃₀Pt₇₀/Fe₃O₄ core/shell nanoparticles under reductive atmosphere and diffusion of iron atoms in shell to Pt-rich core. The core/shell structure was suggested to be an effective way to reduce the ordering temperature obviously.更多还原