The dielectric constant in annealing coercive differential spin tunneling junctions Co/Al-oxide/Co has been investigated in order to clear the influence of thermal annealing on oxidation states. Al oxidized naturally in pure O2 shows the relative dielectric constant of 10-40 before annealing. It indicates that Al oxidized in pure O2 can be AlO2 because the dielectric constant of AlO2 is approximately 22.7. This dielectric measurement result is in good agreement with XPS analysis results that O/Al ratio is 1.9-2.0. After annealing at temperature ranging from room temperature up to 250 °C, the relative dielectric constant approaches approximately 8.0, which is equal to that of Al2O3. This indicates that the phase of Al-oxide is changing from AlO2 to Al2O3 by annealing. This dielectric measurement will help investigate the oxidation state, such as chemical composition for junctions themselves.
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