Enhancement of tunnel magnetoresistance with oxidized AlHf-alloy for a tunnel barrier

We investigated the tunnel magnetoresistance (TMR) with oxidized AlHf-Alloy barrier layer. As a result, at the range of Hf content (C/sub Hf/) from 0 at.% to 70 at.% the enhancement of the tunnel magnetoresistance ratio with the AlHf-oxide barrier was observed, especially, the TMR ratio was greatly increased from 9.6% to 21.4% when the C/sub Hf/ increased from 0 at.% to 17 at.%. Furthermore, we found the enhanced TMR ratio with AlHf layer at thin barrier thickness less than 0.55 nm at which the TMR ratio with Al layer was not observed. And the breakdown voltage was improved with the AlHf-oxide barrier. These results are explained by the consideration that a uniformity of the oxidation in the AlHf layer composed with an amorphous or a nanocrystallized state was better than that in the Al layer composed with the large grain boundaries such as fcc-Al.