Biquadratic coupling through nano-oxide layers in pinned layers of IrMn-based spin valves.

We have investigated the coupling between top and bottom pinned layers through various nano-oxide layers (NOLs) in IrMn-based spin valves. The NOLs were formed by using oxygen-plasma oxidation or natural oxidation on 1 nm metallic layers. By inserting naturally oxidized Co-NOLs in the pinned layer, strong ferromagnetic coupling through NOLs and high specularity at the NOL interface were achieved. In contrast, when the plasma-oxidized Co-NOLs were inserted, ferromagnetic coupling through NOLs disappeared, plausibly due to the formation of nonferromagnetic oxides, which led to a low magnetoresistance (MR). Insertion of naturally oxidized Ni[SUB80]Fe[SUB20]-NOLs showed the same results as that of naturally oxidized Co-NOLs. On the other hand, biquadratic coupling between top and bottom pinned-Co[SUB90]Fe[SUB10] layers was observed by inserting plasma-oxidized Ni[SUB80]Fe[SUB20]-NOLs. The highest MR was obtained when the field was applied along the direction perpendicular to the field-annealing direction. Similar biquadratic coupling was also found with naturally oxidized or plasma-oxidized Fe-NOLs. We suggest that the biquadratic coupling between pinned Co[SUB90]Fe[SUB10] layers through NOLs results from the coupling between Fe (or Co[SUB90]Fe[SUB10] and Fe[SUP+3] oxides. [ABSTRACT FROM AUTHOR]