Tunnel magnetoresistance for coherent spin-flip processes on an interacting quantumdot

Abstract

Spin-polarized electronic tunneling through a quantum dot coupled to ferromagneticelectrodes is investigated within a nonequilibrium Green function approach. Aninterplay between coherent intradot spin-flip transitions, tunneling processes andCoulomb correlations on the dot is studied for current–voltage characteristicsof the tunneling junction in parallel and antiparallel magnetic configurationsof the leads. It is found that due to the spin-flip processes electric current inthe antiparallel configuration tends to the current characteristics in the parallelconfiguration, thus giving rise to suppression of the tunnel magnetoresistance (TMR)between the threshold bias voltages at which the dot energy level becomes active intunneling. Also, the effect of a negative differential conductance in symmetricaljunctions, splitting of the conductance peaks, significant modulation of TMRpeaks around the threshold bias voltages as well as suppression of the diode-likebehavior in asymmetrical junctions is discussed in the context of coherent intradotspin-flip transitions. It is also shown that TMR may be inverted at selected gatevoltages, which qualitatively reproduces the TMR behavior predicted recentlyfor temperatures in the Kondo regime, and observed experimentally beyond theKondo regime for a semiconductor InAs quantum dot coupled to nickel electrodes.