Abstract
Tunnel magnetoresistance (TMR) and spin filter effect in magnetic tunnel junctions are studied by using numerical simulations based on the linear response theory. In Fe/MgO/Fe junction, TMR is calculated for both clean and disordered systems. Large MR ratio obtained in clean junctions is attributed to the momentum and symmetry filter effect of MgO barrier. It is shown that lattice distortions within MgO and at the interfaces decrease the MR ratio because the disorder weakens the filter effects and causes hybridization between Bloch wave functions having different momenta and symmetries. The spin filter effect in junctions containing a ferromagnetic insulator LaNi0.5Mn0.5O3 is also investigated. It is shown that a large spin filter effect is obtained in LaNiO3/LaNi0.5Mn0.5O3/LaNiO3 junctions although the tunnel barrier height is spin independent.
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