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First-principles calculation of the spin-polarized current from transition-metal electrodes

过渡金属电极自旋极化电流的第一性原理计算

基本信息

批准号：
13640337
负责人：
ISHIDA Hiroshi
金额：
$ 1.92万
依托单位：
Nihon University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2003
项目状态：
已结题

项目摘要

The purpose of the present study was to develop a method for calculating the spin-polarized current through transition-metal tunnel junctions and the field-emission current from metal electrodes by a first-principles approach within density-functional theory. In our method, the Green function in the interface region is calculated self-consistently Using the embedding technique of Inglesfield and the linearized augmented plane wave (LAPW) basis set. The details are as follows:1. The electronic structure of the 3-dimensional crystal in the interior of a semi-infinite electrode is determined by the full-potential LAPW method.2. The complex band structure of a crytal corresponding to the Miller index of the electrode surface is calculated from the transfer matrix for 1-electron wave functions.3. The embedding potential of a semi-infinite electrode is constructed from the evanescent and Bloch waves calculated in the step 2.4. The electronic structure of the interface region between two semi-infinite electrodes is computed self-consistently within density functional theory.5. The ballistic current flowing through the 'interface is calculated using the Landauer formula. We reformulated the formula in terms of the Green function and the imaginary part of the embedding potential. In addition, -we have derived a new formula that can treat also the tunnel current from localized surface states.We applied the present formalism to the following systems:1. We investigated field-emission currents from noble metal surfaces and clarified its dependence on the crystal orientation. It has turned out that the tunnel current from localized surface states can make a dominant contribution.2. We investigated the spin-polarized tunnel current through tunnel junctions such as Cu/Co/Cu and also that through Fe/MgO/Fe, which is known as a best candidate for magnetic, random access memory (MRAM).

本研究的目的是利用密度泛函理论中的第一性原理方法，建立一种计算过渡金属隧道结的自旋极化电流和金属电极场发射电流的方法。该方法利用Inglesfield嵌入技术和线性化增广平面波（LAPW）基集自洽地计算界面区域的Green函数。具体操作如下。用全电位LAPW法测定了半无限电极内部三维晶体的电子结构。根据单电子波函数的传递矩阵，计算出晶体与电极表面米勒指数相对应的复杂能带结构。半无限电极的嵌入电位由步骤2.4中计算的倏逝波和布洛赫波构成。在密度泛函理论中，两个半无限电极之间的界面区域的电子结构是自洽的。用兰道尔公式计算通过界面的弹道电流。我们用格林函数和嵌入势的虚部重新表述了公式。此外，我们还推导了一个新的公式，可以从局部表面状态处理隧道电流。我们把现在的形式主义应用到以下系统中：我们研究了贵金属表面的场发射电流，并阐明了其与晶体取向的关系。结果表明，来自局域表面态的隧道电流起主要作用。我们研究了通过Cu/Co/Cu和Fe/MgO/Fe等隧道结的自旋极化隧道电流，这些隧道结被认为是磁性随机存取存储器（MRAM）的最佳候选。