Thermally activated deterioration processes in Co/Cu GMR multilayers

The magnitude of the giant magnetoresistance (GMR) observed in multilayers is known to change irreversibly at elevated temperatures. To improve the th ermal stability of devices, a fundamental understanding of the GMR and its correlation to the temperature-induced structural and morphological changes in a given system is mandatory. We therefore investigated the structural a nd magnetic properties of sputtered Co/Cu multilayers in the pre- and posta nnealed states (temperature regime for annealing up to 750 degreesC) by in situ x-ray diffraction, transport measurements, ferromagnetic resonance (FM R), and magneto-optical Kerr effect (MOKE). We were able to identify a sequ ence of distinct structural changes each of which sets in above a character istic critical temperature. These critical temperatures depend strongly on the thickness of the individual layers. The structural alterations observed range from interfacial sharpening through texture reorientations up to the formation of a granular state, and are associated with distinct in/decreas es of the GMR signal. Using FMR and MOKE we determined in-plane magnetic an isotropies and interlayer coupling for as-grown and annealed samples. (C) 2 001 American Institute of Physics.