Dependence of GMR on NiFe layer thickness in high sensitive simple spin valve

The dependence of the giant magnetoresistance on Ni₈₁Fe₁₉ soft magnetic layer thickness is investigated experimentally for a simple spin valve with a top-pinned structure of Ta (6 nm)/Ni₈₁Fe₁₉/Co₉₀Fe₁₀ (1 nm)/Cu (1.8 nm)/Co₉₀Fe₁₀ (3.5 nm)/Ir₂₀Mn₈₀ (8 nm)/Ta (6 nm). With Ni₈₁Fe₁₉ thickness increased from 6 nm to 7 nm, the magnetoresistance (MR) ratio decreases sharply from 8.34% to 3.34%, whereas it changes only slightly within the thickness ranges from 2-6 nm and from 7-12 nm, and larger MR ratios are obtained in the range from 2-6 nm. For a spin valve with an optimized thickness of Ir₂₀Mn₈₀ (11 nm) and top Ta (3 nm), the MR dependence is in accordance with the former structure when Ni₈₁Fe₁₉ thickness changes from 3.5 to 5.5 nm, and an optimized spin valve with 4.5-nm-thick Ni₈₁Fe₁₉ is obtained. This spin valve has a large MR ratio (9.15%), low coercive force (0.85 Oe), and high sensitivity, which makes it promising for applications.