Interplay of antiferromagnetic coupling in copper/permalloy combination multilayers

The evolution of the giant magnetoresistance (GMR) effect in sputtered combination multilayers (CMLs) of type Py1.8nm//{(Cu1.8nm/Py1.6nm)N/(Cu0.9nm/Py1.6nm)N}y with Py (permalloy=Ni81Fe19) has been investigated at room temperature. It is shown that the GMR characteristic of these CMLs can be phenomenologically predicted, if the physical properties are known, i.e., the GMR effect amplitude, double layer conductance, and bilinear and biquadratic antiferromagnetic exchange coupling constants of the two underlying {Cu/Py}N base systems at the first (Cu0.9nm) and second (Cu1.8nm) antiferromagnetic coupling maximum (AFCM). The GMR characteristic of the simplest CML with N=1 is, e.g., determined by averaging the bilinear and biquadratic exchange coupling constants of the two base systems. The GMR characteristics of CML with N⩾2 are a superposition of that of the underlying {Cu/Py}N base systems weighted by the fraction of the corresponding double layer conductance. Furthermore, it is demonstrated that the CMLs are interesting from an application point of view since they combine the temperature stability of the underlying {Cu/Py}N base system at the second AFCM with a larger GMR effect amplitude.