Hydrothermal Synthesis of Magnetic Single Crystals in Thermally and Chemically Stable Reaction Fields of One-Dimensional Nano Space

通过化学气相沉积丙烯在阳极氧化铝（AAO）薄膜上，使AAO纳米通道的外表面和内表面都被碳完全覆盖。碳包覆纳米通道可以作为模板用于需要强碱性条件的水热处理。在第一年，我们报告了我们在碳包覆纳米通道的空腔中通过水热反应镍化合物合成单晶纳米棒的尝试，并证明了水热合成方法可以应用于基于模板的纳米材料的制备。然而，我们使用这种水热方法在纳米通道中插入铁磁性金属时遇到了一些困难。然后我们发现铁磁性金属（Permalloy）在电镀液中电化学沉积在AAO层的碳包覆纳米通道上。此外，不仅可以沉积像坡莫合金这样的软磁合金，还可以沉积像镍金属这样的硬磁材料。在上述电镀方法中，当我们使用碳包覆的AAO薄膜作为阴极电镀Permalloy时，在纳米管内部没有观察到Permalloy的沉积，而只是在表面上观察到Permalloy的沉积。然后，我们只去除沉积在AAO膜外表面的碳，将碳留在通道内，并在纳米管的腔中发现金属沉积。这是因为电镀进入纳米空间周围的导电材料（碳）是非常困难的。但是，对于高密度磁记录介质的应用，应保留外表面的这种碳层，因为碳可以起到保护和润滑层的作用。因此，我们努力在AAO的碳包覆纳米通道中电化学沉积坡莫合金，并最终通过精确控制电镀条件成功地沉积了坡莫合金。

By chemical vapor deposition of propylene over an anodic aluminum oxide (AAO) film, not only the outer surface but also the inner surface of AAO nanochannels can be fully covered with carbon. The carbon-coated nanochannels can be used as a template in hydrothermal treatment that requires sever alkaline conditions. In the first year we reported our attempt at the synthesis of single crystal nanorods by hydrothermal reaction of nickel compounds in the cavity of the carbon-coated nanochannels and demonstrated that hydrothermal synthesis method can be applied to template-based preparation of nano-sized materials. However, we had some difficulty to insert ferromagnetic metal into the nanochannels using this hydrothermal method. Then we found that ferromagnetic metal (Permalloy) was electrochemically deposited on the carbon-coated nanochannels in the AAO layer in an electroplating bath. Moreover, not only soft magnetic alloy such as Permalloy but also hard magnetic materials such as nickel metal were able to be deposited.In the above electroplating method, Permalloy deposition had never been observed inside the nanotubes, but only on the external surface, when we used the carbon-coated AAO film as a cathode for the electroplating of Permalloy. We then removed only the carbon deposited on the external surface of the AAO film with leaving carbon inside the channels and found metal deposition in the cavity of the nanotubes. This is because electroplating into nano space surrounded by electro-conductive material (carbon) is very difficult. However, for the application of high-density magnetic recoding media, such carbon layer on the external surface should be kept, because the carbon can play a role of a protective and lubricated layer. We thus make every effort to electro-chemically deposit Permalloy in the carbon-coated nanochannels in the AAO and finally have succeeded in such deposition by precisely controlling the electroplating conditions.