Eur. Phys. J. B 82, 37-46 (2011)
https://doi.org/10.1140/epjb/e2011-20149-3

Spin-flip assisted tunneling through quantum dot based magnetic tunnel junctions

¹ Computational Nanoelectronics and Nano-device Laboratory, Electrical and Computer Engineering Department, National University of Singapore, 4 Engineering Drive 3, Singapore, 117576, Singapore
² Information Storage Materials Laboratory, Department of Electrical and Computer Engineering, National University of Singapore, 1 Engineering Drive 3, Singapore, 117576, Singapore
³ Data Storage Institute, A *STAR (Agency of Science, Technology and Research), DSI Building, 5 Engineering Drive 1, Singapore, 117608, Singapore

Corresponding author: ^a michellema82@gmail.com

Received: 1 March 2011
Revised: 13 May 2011
Published online: 29 June 2011

Abstract

We theoretically study the spin-polarized transport through double barrier magnetic tunnel junction (DBMTJ) consisting of the quantum dot sandwiched by two ferromagnetic (FM) leads. The tunneling current through the DBMTJ is evaluated based on the Keldysh nonequilibrium Green's function approach. The self-energy and Green's function of the dot are analytically obtained via the equation of motion method, by systematically incorporating two spin-flip phenomena, namely, intra-dot spin-flip, and spin-flip coupling between the lead and the central dot region. The effects of both spin-flip processes on the spectral functions, tunneling current and tunnel magnetoresistance (TMR) are analyzed. The spin-flip effects result in spin mixing, thus contributing to the spectral function of the off-diagonal Green's function components (). Interestingly, the spin-flip coupling between the lead and dot enhances both the tunneling current and the TMR for applied bias above the threshold voltage V_th. On the other hand, the intra-dot spin-flip results in an additional step in the I-V characteristics near V_th. Additionally, it suppresses the tunneling current but enhances the TMR. The opposing effects of the two types of spin-flip on the tunneling current means that one spin-flip mechanism can be engineered to counteract the other, so as to maintain the tunneling current without reducing the TMR. Their additive effect on the TMR enables the DBMTJ to attain a large tunneling current and high TMR for above threshold bias values.