First-principles methods for spin-polarized transport in magnetic nanojunctions

Foundry Users: Lingzhu Kong, James R. Chelikowsky, University of Texas, Austin

Spintronics, also known as magnetoelectronics, is an emergent technology that exploits the spin degree of freedom of electrons, as well as their charge state The most common spintronic devices, spin-valves, are magnetic multilayers consisting of at least two ferromagnetic layers separated by a nonmagnetic spacer layer. An external magnetic field is used to align magnetization vectors of one of the adjacent ferromagnetic layers parallel or antiparallel, which in turn modulates the resistance.

In spite of recent developments in molecular electronics and spintronics at the nanoscale, little is known at present about spin-polarized transport in magnetic nanoscale junctions, especially in the limit of atomic point contacts. Theoretical studies are important for providing the understanding necessary to control spin transport and spin dynamics. In this study, we will focus on studying spin-dependent properties of the magnetic atomic junctions and their response to external fields. In conjunction with Foundry user James Chelikowsky at UT-Austin, we are developing a method for the electronic transport of nano-scale junctions under finite bias. Our method is based on density functional theory using real space pseudopotentials. Scattering wave functions are obtained by solving a set of linear equations with a sparse coefficient matrix. Our numerical method is novel in that does not require a matrix inversion. We have applied the method to Na or Mg atomic point contacts coupled to two planar electrodes, and good agreement with previous work was obtained. We are now examining spin-dependent transport in Sc magnetic atomic point contacts, where phenomenona such as domain wall scattering, magnetostriction, and orbital blocking are being studied, and where trends in magnetoresistence are examined as a function of junction bias, magnetic moment, and electronic coupling.