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首页> 外文学位 >Structural, microstructural, and magnetic properties of terbium, gadolinium, and samarium cobalt nanoparticles.
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Structural, microstructural, and magnetic properties of terbium, gadolinium, and samarium cobalt nanoparticles.

机译：,、 g和sa钴纳米粒子的结构，微观结构和磁性。

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摘要

Hard magnetic nanoparticles have many applications, such as high density recording media, and magnetic nano-devices. Finite size effects dominate many properties of magnetic nanoparticles. In this work, Tb, Gd, and SmCo 5 nanoparticles with different sizes ( 10 nm) embedded in Cr and W matrices were fabricated via annealing multilayer precursors made by magnetron sputtering. Their structural and magnetic properties were studied with an emphasis on the dependence on particle size and the matrix used.;In Tb and Gd nanoparticles, their thermomagnetic properties (M vs. T) and low-temperature hysteresis behavior were investigated. The Tb nanoparticles showed only one magnetic transition on their M vs. T curves, comparing with bulk samples which have two transitions. This magnetic transition was found to be a true magnetic ordering transition instead of due to superparamagnetic behavior. It was found that both the Curie temperature and the coercivity at T = 5 K increased with the average particle size. As for matrix effect, it was proposed that Tb particles grew much more slowly but uniformly in W matrix than in Cr matrix. The properties of Tb and Gd nanoparticles were compared, and most of the differences could be attributed to the huge differences in their magnetocrystalline anisotropy constants.;As for the SmCo5 nanoparticles, their magnetocrystalline anisotropy and hysteresis behavior at different temperatures were studied with a focus on the room-temperature behavior. The magnetocrystalline anisotropy constants were found to be much lower than bulk values. Giant coercivities were observed. The shapes of their hysteresis loops were related to the magnetic interactions among the SmCo5 grains. The mechanism for magnetization reversal was investigated via initial magnetization curves, Hc vs. Happ plot, and magnetic viscosity measurements. The reversal was found to be by magnetization rotation.
机译：硬磁性纳米粒子具有许多应用，例如高密度记录介质和磁性纳米设备。有限尺寸效应支配了磁性纳米粒子的许多特性。在这项工作中，通过对磁控溅射制备的多层前驱物进行退火，制备了嵌入到Cr和W矩阵中的具有不同尺寸（<10 nm）的Tb，Gd和SmCo 5纳米颗粒。研究了它们的结构和磁性，并着重于对粒径和所用基质的依赖性。在Tb和Gd纳米颗粒中，研究了它们的热磁性质（M对T）和低温磁滞行为。与具有两个跃迁的本体样品相比，Tb纳米颗粒在其M与T曲线上仅显示出一个磁跃迁。发现该磁转变是真正的磁有序转变，而不是由于超顺磁行为。已经发现，在T ＝ 5K时，居里温度和矫顽力均随平均粒径而增加。至于基体效应，有人提出，钨基体中的铬粒子生长比铬基体慢得多，但均匀。比较了Tb和Gd纳米粒子的性能，大部分差异可归因于它们的磁晶各向异性常数的巨大差异。;关于SmCo5纳米粒子，研究了它们在不同温度下的磁晶各向异性和磁滞行为，重点是室温行为。发现磁晶各向异性常数远低于体积值。观察到巨大的矫顽力。其磁滞回线的形状与SmCo5晶粒之间的磁相互作用有关。通过初始磁化曲线，Hc对Happ图以及磁粘度测量研究了磁化反转的机理。发现反转是通过磁化旋转。

著录项

  • 作者

    Yan, Zhicheng.;

  • 作者单位

    University of Delaware.;

  • 授予单位 University of Delaware.;
  • 学科 Physics Condensed Matter.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 215 p.
  • 总页数 215
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;
  • 关键词

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