High conductance magnetoresistive tunnel junctions with multiply oxidized barrier

We have fabricated $\text{8×8\hspace{0.17em}μ}{\mathrm{m}}^{\mathrm{2}}$ mesa junctions from ultrahigh vacuum magnetron sputter-deposited ${\mathrm{Nb/Fe/Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}\mathrm{/Al/CoFe/Nb}$ heterostructures. The ${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}$ barrier was prepared by the technique of multiple oxidation. The effect of multiple oxidation on the junction magnetoresistance (JMR) was investigated. JMR up to 6.2% at room temperature and 9.2% at 77 K was obtained. Junctions with the highest JMR have resistance-area products in the range required for device applications.