Field sensitivity in spin-valve sandwiches with antiferromagnetic NiO films

We have investigated the MR ratios and the field sensitivities in Ni-81/Fe-19/Cu/Ni81Fe19 spin-valve sandwiches grown on antiferromagnetic NiO films as a function of the NiO thickness and the uniaxial deposition field. The MR ratio has a maximum value of 4.5% at 420 Angstrom of NiO and 180 Oe of uniaxial deposition field, and a field sensitivity of 0.6 %/Oe. In older to obtain a higher MR ratio and field sensitivity, we have studied the effects of adding a Co layer between the interfaces of NiFe and Cu and also the effects of a NiO film on top or at bottom on the spin-valve sandwiches. The MR ratios sandwiches with the Co layer increases however, the sensitivity decreases to 0.37 %/Oe due to the high coercivity of Co. The Co inserted structure with the NiO film on top has a low MR ratio of 5.7% and a high sensitivity of 5.8 %/Oe The thermal stability of the sandwiches with the NiO film on top is superior to that of the NiO film at bottom.