First-principles calculations based on density functional theory are used to elucidate the effect of O vacancies, forming centers, on spin-dependent tunneling in magnetic tunnel junctions. O vacancies produce occupied localized states and unoccupied resonant states, which is consistent with available experimental data. The authors find that O vacancies affect the conductance by nonresonant scattering of tunneling electrons causing a substantial reduction of tunneling magnetoresistance (TMR). Improving the quality of the MgO barrier to reduce O vacancy concentration would improve TMR in these and similar junctions.
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Supercells are tetragonal for the 32 atom cell and cubic for the 64 and 216 atom cells with edge sizes and , respectively. is the experimentally observed lattice constant of Fe and .
Supercells are tetragonal with five layers of MgO and six (seven) layers of Fe in the electrodes. The cell sizes are , where is the distance between Fe and O atoms at the interface (Ref. 2).
The transmission probability probes the features of electron tunneling that reveal themselves in the differential conductance at a finite bias voltage. At zero bias the conductance is given by .
