CPP spin-valves utilizing ultra-strong Ir coupled antiparallel pinned layers for thick reference layer stabilization

The magneto-resistance (ΔR/R) of a current-perpendicular-to-the-plane (CPP) spin-valve sensor with an anti-parallel (AP) coupled pinned layer can be increased by increasing the thickness of its reference ferromagnetic layer (AP2) close to the spin-diffusion length of the material employed within AP2 in order to generate more bulk electron spin scattering. However ultra-strong antiferromagnetic coupling is required to maintain a high saturation field in the AP coupled structure, which is one criterion for a stable sensor. We found that Ir coupled anti-parallel (AP) pinned structures can be prepared with an extremely high coupling allowing us to increase the thickness of both the pinned layer,(AP1) and AP2 to more than 100 Å while maintaining both high saturation fields and a balanced AP-pinned structure. Annealing was done at 225°C for 4 hours and the hysteresis loops of the annealed Ta(50)/NiFe(35)/CoFe₁₀(50)/Ir(6)/CoFe₁₀(50)/Ru(50)/Ta(25) sample and the as-deposited sample were compared which showed that Ir coupled structures are unstable against thermal annealing. We grew metallic Ir AP coupled self-pinned CPP spin valves structure which did not require annealing and patterned them into pillars using electron beam lithography and ion milling. The magnetoresistance increased with AP2 layer thickness.