An efficient full-potential linearized augmented plane wave electronic structure method for charge and spin transport through realistic nanoferronic junctions

摘要

Two extensions of the FLAPW electronic structure method are presented, which allow the efficient computation of charge and spin transport properties in realistic nanoferronic materials and nanostructures. First, an order-N implementation of the FLAPW method is presented, which allows the efficient calculation of electronic transport in magnetic tunnel junctions (MTJs) and metallic spin-valves. The method described scales linearly with system size in contrast to the cubic scaling of the computational burden of the standard FLAPW method. The implementation is based on the embedding method, which allows to divide the system into atomic layers, which are then coupled by the embedding potential. Thus, this method is optimally suited for the description of open systems, such as surfaces and tunnel junctions. The order-N implementation allows to exploit the high precision of the FLAPW method at minimal computational cost. The implementation was validated for structural and magnetic properties and charge and spin transport. The method is applied to investigate charge and spin transport and the spin transfer torque in Co/Cu/Co and Fe/Ag/Fe spin valves as well as in Fe/MgO/Fe MTJs. Results are compared to models and experimental data. In addition to system size, difficulties to perform the numerical integration of Fermi sea and Fermi surface integrals can also complicate the computation of charge and spin transport properties. This affects e.g. the anomalous Hall and spin Hall conductivities. In these cases Wannier interpolation provides an efficient framework to perform the numerical k-point integrations. The implementation of maximally localized Wannier functions within the FLAPW method is described and validated for bulk, film and one-dimensional systems with and without spin-orbit coupling. Especially, the ferroelectric polarization of several ferroelectric and multiferroic materials is calculated and discussed based on the Wannier picture of ferroelectric polarization.