Spin polarized tunneling in reactively sputtered tunnel junctions

In order to study spin-polarized electron tunneling, we have grown MOM junctions where M is a magnetic transition metal (Co, Fe or CoFe) and O a reactively sputtered oxide (CoO, NiO, Ta2O5, MgO, HfO2). The oxide thickness ranged between 20 and 300 Å. The structural, magnetic, and transport properties of these junctions have been investigated. Among these various oxides, large magnetoresistance due to spin-polarized tunneling effects have been observed in MgO on the order of 20% at 77 K, and a maximum of 31% has been observed in HfO2 based junctions at 30 K. The other oxides had a much higher tendency to form pinholes and had smaller dielectric breakdown thresholds.