Magnetic, transport, and structural properties of Fe/Co/Cu/[Co/Ir/Co] sandwiches and Fe/Co/Cu/[Co/Ir] multilayers prepared by ion-beam sputtering

A study of the structure, transport, and magnetic properties of Co/Ir sandwiches prepared by ion-beam sputtering is presented. Oscillations of giant magnetoresistance (GMR) and coupling strength versus the Ir thickness are observed. In the spin-valve-type sandwich, at low Ir spacer thickness a shift is observed between GMR and coupling oscillations. This is due to the presence of a magnetic Fe-5nm /Co-0.5nm /Cu-3nm buffer, which has an important contribution to the spin dependent scattering, and also to Be nature of the indirect exchange coupling. The maximum GMR and coupling strength are about 3% and - 0.47 erg/cm(2), respectively. The most interesting result concerns the nature of the indirect exchange coupling as shown by the NMR analysis. This coupling is homogeneous, and consistent with a biquadratic coupling, instead of the usually observed antiferromagnetic coupling. This is further supported by low-temperature magnetization measurements and TEM investigations, which show that the deposited layers are laterally continuous and free of bridges for 0.5-nm Ir spacer layer.