| Budget Amount *help |
¥2,500,000 (Direct Cost: ¥2,500,000)
Fiscal Year 2006: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2005: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Research Abstract |
A large tunnel magnetoresistancce (TMR) as large as 400% has been observed at room temperature in Fe/MgO/Fe junctions. Since the momentum and symmetry of the Bloch states are conserved in eitaxial junctions, MgO serves as momentum-and symmetry-filters. Furthermore, delta-1 band of Fe is half-metallic and, then, MgO is a spin-filter in epitaxial Fe/MgO/Fe junctions, which results in large TMR. However, the effect of disorder on the TMR is not fully understood yet. Ferromagnetic insulator also serves as a spin-filter in different mechanism from MgO. In this work, 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 TMR obtained in clean junctions is attributed to the momentum and symmetry-filter effect of MgO barrier as already shown. It has been found 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 LaNi_<0.5>Mn_<0.5>O_3 has been also investigated. It has been shown that a large spin-filter effect is obtained in LaNiO_3/LaNi_<0.5>Mn_<0.5>O_3/LaNiO_3 junctions although the tunnel barrier height is spin independent. Therefore, in (La-Sr)MnO_3/ LaNiO_3/LaNi_<0.5>Mn_<0.5>O_3/LaNiO_3 junctions, TMR much larger than that observed in Fe/MgO/Fe junctions is expected.
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