D. Waldron

Transport currents can alter order parameter dynamics and change steady states in superconductors, in ferromagnets, and in hybrid systems. In this paper, we present a scheme for fully microscopic evaluation of order parameter dynamics that is intended for application to nanoscale systems. The approach relies on time-dependent mean-field theory, on an adiabatic approximation, and on the use of nonequilibrium Green’s function theory to calculate the influence of a bias voltage across a system on its steady-state density matrix. We apply this scheme to examine the spin-transfer torques which drive magnetization dynamics in $\mathrm{Co}∕\mathrm{Cu}∕\mathrm{Co}$ spin-valve structures. Our microscopic torques are peaked near $\mathrm{Co}∕\mathrm{Cu}$ interfaces, in agreement with most previous pictures, but surprisingly act mainly on Co transition metal $d$ orbitals rather than on $s$ orbitals as generally supposed.

We report on an ab initio study of giant magnetoresistance (GMR) and current-induced torques (CITs) in $\mathrm{Cr}∕\mathrm{Au}∕\mathrm{Cr}$ trilayers that is based on nonequilibrium Green’s functions and spin-density functional theory. We find substantial GMR due primarily to a spin-dependent resonance centered at the $\mathrm{Cr}∕\mathrm{Au}$ interface and predict that the CITs are strong enough to switch the antiferromagnetic order parameter at current densities $\sim 100$ times smaller than switching current densities in ferromagnetic metal circuits. DOI: http://dx.doi.org/10.1103/PhysRevB.75.174428 © 2007 The American Physical Society

We report on an {\em ab-initio} study of giant magnetoresistance (GMR) and current-induced-torques (CITs) in Cr/Au multilayers that is based on non-equilibrium Green's functions and spin density functional theory. We find substantial GMR due primarily to a spin-dependent resonance centered at the Cr/Au interface and predict that the CITs are strong enough to switch the antiferromagnetic order parameter at current-densities $\sim 100$ times smaller than typical ferromagnetic metal circuit switching densities.