Magnetotransport properties of annealed (FeCo)/Ag multilayers

The dependence of the giant magnetoresistance (GMR) on the sputtering pressure, the presence of a Ta underlayer and overlayer, the annealing temperature and the bilayer thickness has been studied in sputtered (Fe-Co)/Ag multilayers. The optimum sputtering pressure was found to be 5 mTorr. The Ta underlayer and overlayer influence greatly the microstructural changes during heat treatment and consequently the magnitude of magnetoresistance. The magnetoresistance increases initially with increasing annealing temperature, reaches a maximum in the region between 250 and 325 °C and after that decreases. The maximum GMR was 8.43% at 46 K and 5.29% at room temperature for films with Ta layers annealed at 275 °C. The magnetic properties are also affected by the annealing. The as-sputtered samples show coercivity in the range 60–220 Oe. After heat treatment in vacuum for 10 min the coercivity drops dramatically in all samples. The films with the highest GMR are believed to be superparamagnetic.