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
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 Vth. On the
other hand, the intra-dot spin-flip results in an additional step in
the I-V characteristics near Vth. 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.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2011