Spin valve sensors with synthetic free and pinned layers

Unshielded spin-valve sensors (6×2 μm2) with both synthetic ferrimagnet free (SF) and synthetic antiferromagnet pinned (SAF) layers are demonstrated, exhibiting high sensitivities, good thermal stability and reduced free layer effective magnetic thickness (teff). The free layer teff can be reduced to ∼10 A while maintaining its physical thickness near 60 A, without significant magnetoresistive signal loss (MR∼6%). After current biasing, the sensors show a linearized response, demonstrating a coherent switching of the synthetic free layer. Sensor sensitivity (S) increases with decreasing free layer effective magnetic thickness (S≈0.5%/Oe at teff=10 A) as expected from the decrease of the free layer demagnetizing field. The coupling field (Hf) between the free and pinned layers increases with decreasing teff (Hf∝Ms2/(teffMefff)). The sensors are thermally stable upon anneals up to 300 °C.