Antiferromagnetic Coupling in NiFe/Co/Cu/Co Sandwiches

Maximum Δρ/ρ change exceeding 4% for a magnetic field increase of 4 Oe is obtained at room temperature in NiFe/Co/Cu/Co sandwiches when two ferromagnetic components, NiFe/Co and Co, with different coercivities are magnetically coupled across a nonmagnetic Cu spacer. It is shown that the MR ratio oscillates as a function of Cu layer thickness and that the magnetic moment decreases under magnetically coupled states. This suggests the presence of antiferromagnetic coupling between the two ferromagnetic components. The measuring field direction which causes high sensitivity for a large MR change rotates perpendicularly to the intrinsic anisotropy axis at about 2.8 nm. This rotating spin-axis direction and very high sensitivity are thought to be due to the phenomenon known as spin flopping associated with antiferromagnetic coupling.