[Co/Ni] $_{\rm N}$ -Based Synthetic Antiferromagnet With Perpendicular Anisotropy and Its Application in Pseudo Spin Valves

The dependence of magnetic properties on layer repetition number and Ru thicknesses have been studied for perpendicularly magnetized synthetic antiferromagnet (SAF) in a structure of [Co/Ni]_N/Ru/[Co/Ni]₃. The optimum SAF with strong antiferromangetic coupling field and large switching field of the net magnetization have been determined and utilized as the reference layer in the pseudo spin valves. Compared with the rapid drop of GMR signal for the normal [Co/Ni]-based pseudo spin valves after annealing at low temperature (T_a) of 150°C, the spin valve with SAF reference layer exhibits much stable thermal stability due to the large switching field difference between the free and reference layers which avoids the simultaneous magnetization rotation. The GMR signal of the SAF spin valve sample is 6.0% at room temperature, it decreases very gradually with the increase of T_a. We attribute the slow GMR reduction observed in the SAF spin valve to the effects of domain formation and perpendicular anisotropy deterioration caused by high temperature anneals.