Interplay between exchange biasing and interlayer exchange coupling in Ni₈₀Fe₂₀/Cu/Ni₈₀Fe₂₀/Fe ₅₀Mn₅₀ layered systems

Magnetoresistance curves have been measured for 80 Å Ni ₈₀Fe₂₀/t_Cu Cu/60 Å Ni₈₀Fe ₂₀/80 Å Fe₅₀Mn₅₀ layered systems (t _Cu=9-93 Å). After separating the contributions from anisotropic magnetoresistance and spin valve or giant magnetoresistance (GMR), the GMR curves were interpreted in terms of a minimum-energy model for the magnetization orientation of the Ni₈₀Fe₂₀ layers. The interlayer exchange coupling was found to be purely ferromagnetic, and monotonically decreasing with increasing t_Cu. The interplay of this coupling with the exchange biasing effect results in a critical interlayer thickness, t ^crit_Cu=15 Å, below which no perfect antiparallel alignment of the Ni₈₀Fe₂₀ magnetizations can be realized. The GMR, which would otherwise increase with decreasing Cu layer thickness, is therefore expected to reach a maximum at or slightly below t^crit _Cu. Indeed, such a maximum was found (with ΔR/R=4.3%) at t _Cu=22 Å, a value well above t^crit_Cu. This is attributed to the occurence of inhomogeneities in the interlayer exchange coupling.