Structure of Ordered and Disordered Systems

有序和无序系统的结构

• 批准号: 5343-2007
• 负责人: Crozier, Daryl
• 金额: $ 1.78万
• 依托单位: Simon Fraser University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2007
• 资助国家: 加拿大
• 起止时间: 2007-01-01 至 2008-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=363371
• 关键词: Structure; Ordered; Disordered; Systems

My principal interest is the structure of magnetic nanostructures engineered from ferromagnetic/ non-ferro- magnetic layers epitaxially grown on semiconductors.  The correct interpretation of the magnetic behaviour in such systems- the magnetic anisotropy and interlayer coupling- is strongly dependent on the nature of the interface between layers, the strain in the layers and the extent of any interdiffusion or reaction between layers and substrate. The same factors are important to improving spintronic devices which depend upon the efficiency with which an electron carries its spin through a metal-semiconductor interface.   We examine these factors with synchrotron radiation structural techniques applied in situ in two molecular beam epitaxy (MBE) facilities which we constructed at the PNC/XOR (Pacific Northwest Consortium/ X-ray Optics and Research) beamlines, Advanced Photon Source, IL. We study metallic films as they are grown epitaxially, layer by layer. Our structural techniques include XAFS (x-ray absorption fine structure), specular and diffuse x-ray reflectivity, x-ray standing waves and surface x-ray diffraction. We have examined extensively Fe/GaAs, Pd/Fe/GaAs and Fe/Pd/Fe/GaAs and will continue with related systems.    A persistent problem is the origin of the uniaxial  in-plane magnetic crystalline anisotropy at the  Fe-GaAs interface. We have found an in-plane structural anisotropy for 2 ML Fe but not for 4 ML and thicker films. We will determine if the in-plane structural anisotropy is a universal feature, independent of the surface reconstruction of GaAs. At the submonolayer level we will attempt to determine if a Fe-GaAs complex forms at the interface and what is its "crystal" structure. We will also look for Fe complexes at the Fe/AlGaAs interface in Fe/AlGaAs/GaAs which has a high electron spin-injection efficiency.    We are examining spin dynamics in ferrimagnetic amorphous GdCo alloys. In a sub-nanosecond  time- resolved experiment we pulse the sample temperature with the PNC/XOR 200 femtosecond laser and use x-ray magnetic circular dischroism to follow the magnetization as the Gd and Co sub-lattices re-orient.

我的主要兴趣是在半导体上外延生长的铁磁/非铁磁层所设计的磁性纳米结构。对这种体系中磁性行为的正确解释——磁性各向异性和层间耦合——在很大程度上取决于层间界面的性质、层内的应变以及层与基体之间任何相互扩散或反应的程度。同样的因素对于改进自旋电子器件也很重要，这些器件依赖于电子通过金属-半导体界面携带自旋的效率。我们在PNC/XOR（太平洋西北联盟/ x射线光学和研究）先进光子源的光束线上建造了两个分子束外延（MBE）设施，利用同步辐射结构技术对这些因素进行了原位研究。我们研究了金属薄膜的外延生长，一层一层。我们的结构技术包括XAFS （x射线吸收精细结构），镜面和漫射x射线反射率，x射线驻波和表面x射线衍射。我们已经广泛地研究了Fe/GaAs， Pd/Fe/GaAs和Fe/Pd/Fe/GaAs，并将继续研究相关系统。一个长期存在的问题是在Fe-GaAs界面的单轴面内磁晶各向异性的来源。我们发现在2ml Fe薄膜中存在平面内结构各向异性，而在4ml和更厚的薄膜中则没有。我们将确定面内结构各向异性是否是一个普遍的特征，独立于GaAs的表面重建。在亚单层水平上，我们将尝试确定Fe-GaAs复合物是否在界面上形成，以及它的“晶体”结构是什么。我们还将在Fe/AlGaAs/GaAs中寻找具有高电子自旋注入效率的Fe/AlGaAs界面的Fe配合物。我们正在研究铁磁性非晶GdCo合金的自旋动力学。在亚纳秒时间分辨实验中，我们使用PNC/XOR 200飞秒激光脉冲测量样品温度，并使用x射线磁圆不同色性跟踪Gd和Co亚晶格重新定向时的磁化情况。