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首页> 外文学位 >Influence of surface structure on the magnetic properties of RF plasma synthesized nickel-zinc ferrite nanoparticles.
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Influence of surface structure on the magnetic properties of RF plasma synthesized nickel-zinc ferrite nanoparticles.

机译：表面结构对射频等离子体合成的镍锌铁氧体纳米粒子磁性能的影响。

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摘要

The development of magnetic materials for use in passive components for high-frequency applications will have far-reaching implications on the improved performance of power and high temperature electronic circuits. Ferrites are the most important materials for these applications because of their large resistivities, low conductive losses and reasonably high permeabilities. NiZn ferrites are the only materials that can be used in microwave applications (GHz range) such as power supply cores, because they have the highest resistivity among the ferrites. Many fundamental magnetic length scales like the single domain size, exchange length and high frequency penetration depths are on the order of 10–100 nm. Therefore the ability to tailor the microstructures of magnetic materials on the nano-scale will have far reaching implications for optimizing the performance of devices. In nanocrystalline ferrites, the symmetry and coordination of cations at the surface coordination polyhedral units may contribute differently to properties like magnetocrystalline anisotropy than in the bulk.;In this thesis, the influence of the polyhedral surface structure on the magnetic properties of NiZn ferrite nanoparticles synthesized using a TEKNA PL 50 RF induction plasma torch have been studied. The surface structure has been explored by TEM and complementary spectroscopic techniques-Mössbauer and EXAFS. The smallest nanoparticles exhibited perfectly octahedral shapes (only (111) surfaces), while the larger particles are truncated octahedral in shape (with more (111) type surfaces than (100) surfaces). The surface structure has been modeled with the various tilings of the tetrahedral and octahedral polyhedral units of the spinel structure on different surfaces. The contribution of the observed faceting behavior to the surface magnetic anisotropy of the (100) and the (111) surfaces will be discussed to interpret the dynamic transverse susceptibility and low temperature static magnetic measurements on these systems. A surface structure model has been proposed to explain surface spin canting and magnetic anisotropy for the observed (111) and (100) nanoparticle surfaces in the polydisperse as well as the chemically size-selected monodisperse nanoparticles. A decomposition model has also been proposed to explain the variations in chemistry within a single nanoparticle and this model has been used to interpret the sintering behavior of the as-synthesized nanoparticles.
机译：用于高频应用的无源元件中的磁性材料的开发将对电源和高温电子电路性能的提高产生深远的影响。铁氧体由于其大的电阻率，低的导电损耗和相当高的磁导率而成为最重要的材料。 NiZn铁氧体是唯一可用于微波应用（GHz范围）（例如电源核心）的材料，因为它们在铁氧体中具有最高的电阻率。许多基本的磁性长度尺度（如单畴尺寸，交换长度和高频穿透深度）约为10–100 nm。因此，在纳米尺度上定制磁性材料的微观结构的能力将对优化器件性能产生深远的影响。在纳米晶铁氧体中，表面配位多面体单元上阳离子的对称性和配位对磁晶各向异性等性质的贡献可能与在体相中的贡献不同；本文研究了多面体表面结构对合成的NiZn铁氧体纳米颗粒的磁性的影响已经研究了使用TEKNA PL 50 RF感应等离子炬。表面结构已通过TEM和互补光谱技术-Mössbauer和EXAFS进行了探索。最小的纳米粒子表现出完美的八面体形状（只有（111）个表面），而较大的粒子呈截头八面体形状（（111个）类型的表面多于（100个）表面。用尖晶石结构在不同表面上的四面体和八面体多面体单元的各种平铺模型化了表面结构。将讨论观察到的刻面行为对（100）和（111）表面的表面磁各向异性的贡献，以解释这些系统上的动态横向磁化率和低温静态磁测量。已经提出了一种表面结构模型来解释多分散体以及化学尺寸选择的单分散纳米颗粒中观察到的（111）和（100）纳米颗粒表面的表面自旋倾斜和磁各向异性。还提出了分解模型来解释单个纳米颗粒内化学性质的变化，并且该模型已用于解释合成后的纳米颗粒的烧结行为。

著录项

  • 作者

    Swaminathan, Rajasekaran.;

  • 作者单位

    Carnegie Mellon University.;

  • 授予单位 Carnegie Mellon University.;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2005
  • 页码 138 p.
  • 总页数 138
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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