First principles study of atomic-scale Al2O3 films as insulators for magnetic tunnel junctions

We performed density-functional calculations with Al/Al2O3/Al structures as models to study Al2O3 tunnel barriers for magnetic tunnel junctions. We fo und that aluminum oxide films thicker than 4.6 Angstrom have pseudogaps wit hout substantial gap states, which suggests that these films have good insu lating properties. This finding is consistent with an experimental result w here a large magnetoresistance ratio was attained with a film thickness of about 8 Angstrom.