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

本研究的目的是发展一种方法来计算自旋极化电流通过过渡金属隧道结和场发射电流从金属电极的密度泛函理论的第一性原理方法。在我们的方法中，利用Inglesfield的嵌入技术和线性增广平面波（LAPW）基组自洽地计算了界面区的绿色函数。具体如下：1.用全电势LAPW方法确定了半无限电极内部三维晶体的电子结构.由单电子波函数的转移矩阵计算了电极表面米勒指数对应的晶体的复能带结构.半无限电极的嵌入电势由步骤2.4中计算的倏逝波和布洛赫波构造。利用密度泛函理论自洽地计算了两个半无限电极之间界面区的电子结构.使用Landauer公式计算了流过界面的弹道电流。我们用绿色函数和嵌入势的虚部重新表述了公式。此外，我们还导出了一个新的公式，该公式也可以处理局域表面态的隧道电流。我们研究了贵金属表面的场发射电流，并阐明了它对晶体取向的依赖性。结果表明，来自局域表面态的隧道电流可以起主导作用.我们研究了自旋极化隧道电流通过隧道结，如Cu/Co/Cu，也通过Fe/MgO/Fe，这是已知的磁性，随机存取存储器（MRAM）的最佳候选人。

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).