Thermal stability and degradation mechanism of NiFe/Cu giant magnetoresistance multilayer systems

Abstract

Ni 80 Fe 20 / Cu multilayers show large giant magnetoresistance (GMR) at low magnetic saturation fields. The GMR signal is known to degrade irreversibly at elevated temperatures. Clarification of the relevant deterioration mechanisms refines our basic understanding of the GMR effect and may help to improve the thermal stability of devices. We therefore investigated structural, transport, and magnetic properties of sputtered Ni80Fe20/Cu multilayers in the as-deposited state and after different anneals (up to 600 °C) by x-ray techniques, transport measurements, ferromagnetic resonance (FMR), and magneto-optical Kerr effect (MOKE). Multilayers with the second maximum of the antiferromagnetic (afm) coupling showed a sharp drop of the GMR at about 250 °C. The changes of the transport properties were associated with a series of structural alterations. These ranged from grain growth and defect reduction through texture sharpening and stress evolution up to the onset of interdiffusion. Interdiffusion changed the NiFe layer composition and the interface structure and finally caused layer intermixing with a loss of the former multilayer structure. Further insight into the magnetic behavior was gained from FMR and MOKE measurements, from which we determined the in-plane magnetic anisotropies, the strength of the afm coupling (bilinear and biquadratic), and the homogeneity of the layer magnetization as a function of the annealing temperature.