Magnetoresistance of ion-beam deposited Co/Cu/Co and NiFe/Co/Cu/Co/NiFe spin valves

Giant magnetoresistance (GMR) films produced by ion-beam deposition (IBD) have been studied much less than material produced by other techniques such as magnetron or diode sputtering. Although the process control aspects that are unique to IBD seem ideal for such work, the reported MR values for IBD material are often lower and the material resistivities higher than for conventional sputter-deposited films. We have used a carefully optimized ion-beam process to produce high-quality spin valves of Co/Cu/Co and NiFe/Co/Cu/Co/NiFe. The MR characteristics were studied as a function of the layer thickness for structures that were top pinned with FeMn and bottom-pinned structures grown on NiO. Using a 25 Angstrom thick Cu layer, the MR of top-pinned Co/Cu/Co reached 8.4% over a fairly wide range of top and bottom Co thickness. In contrast, the MR of such films grown on NiO exhibited a strong dependence on the thickness of both Co layers and peaked at 9.9%. The thickness dependence is strong evidence for specular scattering effects at the external interfaces, although it is at least partly an indirect result of the weak exchange bias provided by the NiO in some samples. The symmetric spin valve structure, NiO/Co/Cu/Co/Cu/Co/ FeMn, produced our highest MR of 12.1%. The NiFe/Co/Cu/Co/NiFe structures we studied were not optimized for maximum MR, but instead had much different top and bottom NiFe thicknesses as is appropriate in pseudospin-valve material for memory elements. Spin valves of this type had a maximum MR of 7.2%. (C) 1999 American Institute of Physics. [S0021-8979(99)48308-2].