Synthesis, Structure and Properties of Magnetic Nanocrystalsand Nanocrystalline Arrays

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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. ***