Synthesis, Structure and Properties of Magnetic Nanocrystalsand Nanocrystalline Arrays

本研究通过磁性纳米晶体的合成和表征来探索其独特的性能。该研究延续了之前的研究成果，通过改变合金化学、纳米晶体形态和界面结构来影响磁性纳米晶体和纳米晶体阵列的磁性各向异性。纳米晶体和纳米晶体阵列的磁各向异性取决于磁晶体的各向异性、形状各向异性、界面各向异性和/或磁弹性耦合提供的各向异性。这些问题在(1)c包覆纳米颗粒中得到解决；(2)碳化物纳米棒填充碳纳米管；(3)在具有铁磁性或亚铁磁性的介孔硅酸盐中渗透、周期性排列的孔隙。等离子体合成产生的纳米颗粒通常是球形的，并且不受益于形状各向异性作为热激活磁化开关的障碍。本研究详细探讨了形状各向异性对新型纳米颗粒和纳米颗粒阵列的影响，其中磁性颗粒的大长宽比可以利用形状各向异性。通过比较具有碳和氧化物涂层的纳米颗粒的磁性能，解决了界面各向异性的问题。本研究旨在了解纳米颗粒中的磁反转机制，以确定各种磁性应用的基本限制。纳米团簇已经证明了不同于块状晶体固体的特性。纳米晶体形式的例子包括巴基球和巴基管，c涂层纳米粒子和纳米棒，以及其他自组装结构。了解这些材料的特性可以开发出具有多种应用的新材料。＊＊＊

9803700 McHenry This research explores through synthesis and characterization the unique properties of magnetic nanocrystals. It continues a previous effort on varying alloy chemistry, nanocrystal morphology, and interfacial structure to influence the magnetic anisotropy in magnetic nanocrystals and nanocrystalline arrays. Magnetic anisotropy in nanocrystals and nanocrystalline arrays depends on magnetic crystalline anisotropy, shape anisotropy, interfacial anisotropy, and/or the anisotropy provided by magnetoelastic coupling. These issues are addressed in (1) C-coated nanoparticles; (2) filled C- nanotubes with carbide nanorods; and (3) infiltrated, periodically arranged pores in mesoporous silicates with ferromagnetic or ferrimagnetic species. Nanoparticles produced by plasma synthesis are usually spherical and do not benefit from shape anisotropy as a barrier to the thermally activated switching of the magnetization. The research examines the effects of shape anisotropy in detail in novel nanoparticles and nanoparticle arrays in which large aspect ratios in the magnetic particles can be used to exploit shape anisotropy. Issues of interfacial anisotropy are addressed by comparing the magnetic properties of nanoparticles having carbon and oxide coatings. %%% This research is aimed at understanding the magnetic reversal mechanisms in nanoparticles in order to determine fundamental limitations for a variety of magnetic applications. Nanosized clusters have demonstrated properties that differ from those of bulk crystalline solids. Examples of nanocrystalline forms include Buckyballs and Buckytubes, C-coated nanoparticles and nanorods, and other self-assembled structures. Understanding properties of these materials enables the development of novel materials with a host of applications. ***