Giant magnetoresistance and high sensitivity in annealed NiFeCo/Ag multilayers

We report giant magnetoresistance in annealed NiFeCo (2 nm)/Ag (3.3 nm) multilayers. For all samples, post-deposition annealing was necessary for the observation of GMR analogous to the NiFe/Ag discontinuous multilayer system. The GMR ratio and field sensitivity varied widely as a function of annealing from temperatures between 300 and 400 °C. A high MR ratio of 6.3% and field sensitivity of 11.3%/(kA/m) (0.9%/Oe) were observed for a seven bilayer sample annealed to 350 °C. In general, NiFeCo/Ag multilayers produced greater MR responses and field sensitivities than comparably annealed NiFe/Ag multilayers. NiFeCo/Ag multilayers, however, display more hysteresis than NiFe/Ag multilayers and lack a zero-crossing saturation magnetostriction versus annealing temperature. Multilayer deposition in a magnetic field severely degrades MR performance since it prevents the magnetostatic antiparallel alignment between magnetic grains which occurs in the absence of an applied magnetic field following sample annealing.