Basic research for the development of portable compact magnetic memory using high coercivity magnetic nanoparticle

本项目详细研究了利用“多元醇法”的化学方法合成磁性金属和合金纳米颗粒。利用多元醇种类、合成温度、金属离子浓度、反应促进剂、成核剂等反应参数有效控制反应动力学，获得具有粒径、晶体结构等物理性能要求的磁性纳米颗粒。这为合成具有不同磁性质的磁性纳米颗粒铺平了道路。以钴、镍等过渡金属纳米颗粒为例，实现了直径从几微米到几十纳米不等、晶体结构各异的纳米颗粒的合成。例如，已知大块钴在高达421.5℃时具有fcc相。然而，用改性多元醇工艺合成的钴金属颗粒具有微米级的fcc结构。当反应动力学增强时，颗粒尺寸减小到亚微米级甚至几十纳米级。随着晶粒尺寸的减小，晶体结构也从微米级的fcc、亚微米级fcc与hcp共存，转变为纳米级的s和hcp钴。另一方面，我们也成功地合成了直径几十纳米的非磁性hcp-Ni纳米颗粒。在磁记录用磁性合金纳米颗粒的合成方面，我们成功地展示了在553 K低温下，使用“改良多元醇法”直接合成L1_0 FePt纳米颗粒，无需后续退火，其直径为5-10 nm，本质磁晶各向异性场（H_k）为31 kOe。这表明，精确控制反应动力学，特别是通过优化多元醇/Pt盐摩尔比和多元醇类型来降低还原率，对于直接合成L1_0 FePt纳米粒子是非常重要的。采用改性多元醇工艺制备了具有高磁晶各向异性、粒径为7 nm的CoPt纳米颗粒。此外，我们还成功地利用APTS作为耦合层将FePt和CoPt纳米颗粒选择性地固定在硅衬底上，即使在更高的退火温度下也能阻止晶粒生长。虽然确定了高各向异性相的存在，但粒子的电位远低于预期值。虽然利用磁性颗粒成功制备便携式紧凑存储器的记录介质尚未实现，但收集了大量与纳米颗粒合成和纳米颗粒单层膜制备相关的信息和知识。因此，以这些信息为基础，我们将朝着高密度记录介质的发展而努力。少

In this project, the synthesis of magnetic metal and alloy nanoparticles by using the chemical method called "polyol process" was investigated in detail. The reaction parameters such as type of polyol, synthesis temperature, metal ion concentration, reaction promoting agents, and nucleating agents were effectively utilized to control the reaction kinetics to obtain magnetic nanoparticles with required physical properties such as size and crystal structure. This paved the way for the synthesis of magnetic nanoparticles with varying magnetic properties. For example in the cases of transition metal nanoparticles such as cobalt and nickel, the synthesis of particles with diameters ranging from few micron to few tens of nanometer and varying crystal structures was realized. For example, the bulk cobalt is known to have fcc phase at temperatures as high as 421.5℃. However, the cobalt metal particles synthesized using the modified polyol process were found to posses fcc structure at micron si … More ze levels. When the reaction kinetics was enhanced, the particle size was reduced to submicron and even to few tens of nanometer. Along with size reduction, the crystal structure also changed from fcc at micron size range, coexistence of fcc and hcp in the submicron size range and to s and hcp cobalt at nanometer size range. On the other hand, we also succeeded in the synthesis of non-magnetic hcp-Ni nanoparticle of few tens of nanometer in diameter.In the case of the synthesis of magnetic alloy nanoparticles for magnetic recording, we have successfully demonstrated the direct synthesis of L1_0 FePt nanoparticles at low temperature of 553 K using "modified polyol method" without subsequent annealing, whose diameter is 5-10 nm and the intrinsic magnetocrystalline anisotropy field (H_k) is 31 kOe. This indicates that precise control of the reaction kinetics, especially low reduction rate through optimizing the polyol/Pt salt mole ratio and type of polyol are very important for directly synthesizing the L1_0 FePt nanoparticles. CoPt nanoparticles with high magnetocrystalline anisotropy and also particle sizes of 7 nm in diameter were prepared by using the modified polyol process. Furthermore, we also succeeded in selectively fixing FePt and CoPt nanoparticles on a silicon substrate by using APTS as the coupling layer, which prevents the grain growth even at higher annealing temperatures. Though the presence of the highly anisotropic phases was identified the potential of the particles were well below the anticipated values. Although the successful fabrication of recording media using magnetic particles for portable compact memory was not realized, considerable information and knowledge related to both the synthesis of nanoparticles and the fabrication of nanoparticle monolayer film was gathered. Thus, using this information as the base, we will work towards the development of high-density recording medium. Less