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Correlation Between Microstructure and Properties in Magnetic Multilayer Nanostructures.

机译：磁性多层纳米结构的微观结构与性能之间的相关性。

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摘要

The properties of layered magnetic nanostructures depend critically on their underlying microstructure. A magnetic tunnel junction (MTJ) is one such multilayer nanostructure that has found technological significance as the read-head sensor in hard disk drives. An MTJ exhibits a difference in the electrical resistance across the junction as a function of the relative orientation of the magnetization in two ferromagnetic electrodes that are separated by a thin dielectric layer [tunnel magnetoresistance (TMR)]. There is, however, a great deal that is not understood about the fundamental correlations between the microstructure and the magnetic and magnetotransport properties of these important nanostructures.;In this thesis, the correlations between the microstructure and the magnetic and magnetotransport behavior of MgO-based MTJs, which exhibit an exceptionally large TMR effect, are studied in detail. Three-dimensional atom-probe tomography and transmission electron microscopy are used to analyze the crystal structure and three-dimensional elemental distribution within CoFe/MgO and CoFeB/MgO MTJs as a function of annealing temperature, deposition conditions, multilayer stack design and layer composition. Annealing between 300--380ºC causes the diffusion of Co, Fe, B and other elements, which affects the symmetry of the tunnel barrier potential. Amorphous CoFeB layers partially crystallize upon annealing, resulting in the diffusion of B out of the crystallized grains of CoFeB. The distribution of B after annealing is found to play a critical role in both the magnetic and magnetotransport behavior of the MTJ. It is found that the B distribution can be controlled to some extent by optimization of the growth parameters and multilayer stack design.;Micromagnetic simulations of the magnetization dynamics in patterned magnetic multilayers, which are similar to those found in MTJs, in response to an applied magnetic field were also performed. The effects of circular exchange bias and interlayer exchange coupling between two ferromagnetic layers on the low-frequency gyrotropic and low-lying eigenmode magnetic responses are described in detail. Increasing the strength of the exchange bias increases the frequency of the dynamic response while the sign and strength of interlayer exchange coupling is found to affect both the static and dynamic behavior of the heterostructure.
机译：层状磁性纳米结构的性质关键取决于其下面的微观结构。磁性隧道结（MTJ）就是这样一种多层纳米结构，它已作为硬盘驱动器中的读头传感器而具有技术意义。 MTJ在通过薄介电层[隧道磁阻（TMR）]隔开的两个铁磁电极中，跨结的电阻随磁化强度相对方向的变化而变化。然而，关于这些重要的纳米结构的微观结构与磁和磁输运性质之间的基本相关性，还有很多尚未被理解。；本论文中，基于MgO的微观结构与磁和磁输运行为之间的相关性详细研究了表现出特别大的TMR效果的MTJ。三维原子探针层析成像和透射电子显微镜用于分析CoFe / MgO和CoFeB / MgO MTJ内的晶体结构和三维元素分布，其与退火温度，沉积条件，多层堆叠设计和层组成有关。在300--380ºC之间进行退火会导致Co，Fe，B和其他元素的扩散，从而影响隧道势垒势的对称性。非晶态的CoFeB层在退火时会部分结晶，导致B从CoFeB的结晶晶粒中扩散出来。发现退火后B的分布在MTJ的磁和磁传输行为中都起着关键作用。发现通过优化生长参数和多层堆叠设计可以在一定程度上控制B分布。响应于应用，图案化磁性多层中磁化动力学的微磁模拟与MTJ中的模拟相似。磁场也被执行。详细描述了两个铁磁层之间的圆形交换偏压和层间交换耦合对低频回旋和低本征模磁响应的影响。交换偏置强度的增加会增加动态响应的频率，而层间交换耦合的符号和强度会影响异质结构的静态和动态行为。

著录项

  • 作者

    Schreiber, Daniel K.;

  • 作者单位

    Northwestern University.;

  • 授予单位 Northwestern University.;
  • 学科 Physics Condensed Matter.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2011
  • 页码 336 p.
  • 总页数 336
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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