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

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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).