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首页> 外文会议>NATO Advanced Study Institute on Magnetic Storage Systems Beyond 2000, Jun 25-Jul 7, 2000, Rhodes, Greece >SYNTHESIS OF PASSIVATED COBALT NANOCRYSTAL ARRAYS WITH CONTROLLED SIZE AND SHAPE
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SYNTHESIS OF PASSIVATED COBALT NANOCRYSTAL ARRAYS WITH CONTROLLED SIZE AND SHAPE

机译：尺寸和形状受控的钝化钴纳米晶的合成

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Rapid pyrolysis of cobalt carbonyl in an inert atmosphere was employed to produce magnetic colloids (ferrofluids) of monodispersed, stabilized, cobalt nanocrystals. The size distribution and the shape of the nanocrystals were controlled by varying the surfactant (oleic acid, phosphonic oxides and acids...), its concentration and the reaction temperature. Thus, we systematically synthetised passivated nanocrystals with nearly monodisperse (std. Dev.< 5%) size ranging from 3 to 17 nm. The surface tension of the Co crystals were modified during the reaction and cubic and prism-like crystals of size ～20-30 nm were also synthesized. Particles are single crystals with a complex cubic structure related to the beta phase of manganese (ε-Co). Thus by controlling the size, the shape and the crystal structure the superparamagnetic transition can be customized. These particles have been observed to produce 2D self-assemblies when evaporated at low rates in a controlled atmosphere. A combination of x-ray powder diffraction, transmission electron microscopy and vibrating sample magnetometer has been used to characterize both the dispersed nanocrystals and the assembled superlattices. Nanoscale and nanoparticle materials are a new generation of advanced materials that are expected to exhibit unusual chemical and physical properties different from those of either the bulk materials or single atoms. Decisive structural differences between bulk and nanosized particles have been observed, the most fundamental relationship being between particle size and electronic behavior~1. Magnetic storage technology is rapidly advancing toward its scaling limits. Thin granular films of sputtered ferromagnetic nanocrystals are the basis of conventional magnetic storage (hard drives). Progress in magnetic recording density is due, in part, to the development of media with increasingly finer grain sizes. However, to have a meaningful signal to noise ratio in the recorded signal, the number of grains needed to store a bit is about thousand grains~2. The study of magnetic nanoparticles is of both fundamental interest and pressing technical interest as the grain size of the advanced recording media is rapidly shrinking toward superparamagnetic sizes (about 10 nm for Co hcp), where the 100 Gb/in~2-l Tb/in~2 density would be approached at the one-bit-per-particle limit.
机译：在惰性气氛中快速热解羰基钴，以产生单分散的，稳定的钴纳米晶体的磁性胶体（铁磁流体）。通过改变表面活性剂（油酸，氧化膦和酸等），其浓度和反应温度来控制纳米晶体的尺寸分布和形状。因此，我们系统地合成了钝化的纳米晶体，其纳米粒子的单分散（标准偏差<5％）范围为3至17 nm。反应过程中改变了Co晶体的表面张力，并合成了大小约20-30 nm的立方和棱柱状晶体。颗粒是具有与锰的β相（ε-Co）相关的复杂立方结构的单晶。因此，通过控制尺寸，形状和晶体结构，可以定制超顺磁转变。已经观察到，这些颗粒在受控气氛中以低速蒸发时会产生2D自组装。 X射线粉末衍射，透射电子显微镜和振动样品磁力计的组合已用于表征分散的纳米晶体和组装的超晶格。纳米级和纳米粒子材料是新一代的先进材料，它们有望表现出与本体材料或单个原子不同的化学和物理特性。已经观察到块状和纳米级颗粒之间的决定性结构差异，最基本的关系是粒度与电子行为〜1之间。磁存储技术正在迅速朝着其扩展极限发展。溅射的铁磁纳米晶体的薄颗粒膜是常规磁存储（硬盘驱动器）的基础。磁记录密度的提高部分归因于晶粒尺寸越来越细的介质的发展。然而，为了在记录的信号中具有有意义的信噪比，存储一点所需的颗粒数约为数千个颗粒〜2。磁性纳米颗粒的研究既具有基本意义，也​​具有紧迫的技术意义，因为高级记录介质的晶粒尺寸正朝着超顺磁性尺寸（Co hcp约为10 nm）迅速缩小，其中100 Gb / in〜2-l Tb / in〜2密度将接近每粒子一位限制。

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