Effects of (Ni0.8Fe0.2)100−xCrx seed layer on microstructure, magnetic properties, and giant magnetoresistance of [FeCoNi/Cu] multilayer films

We studied the effect of the (Ni0.8Fe0.2)100−xCrx seed layer on the current-in-plane giant magnetoresistance (CIP-GMR) in Fe16Co66Ni18/Cu multilayer films. Both the GMR ratio (ΔR/R) and interlayer exchange coupling (IEC) between the FeCoNi layers showed strong dependences on the Cr concentration x in the seed layer. The highest ΔR/R of ∼30% was obtained for x = 38 (at. %) due to a comparatively strong antiparallel IEC resulting from a strong [111]-out-of-plane-texture of the [FeCoNi/Cu] multilayer. This confirms that a strong [111] texture is essential for the GMR in antiferromagnetically coupled multilayers as reported in previous works. However, we found that the strong [111] texture is not sufficient to obtain large ΔR/R. For x = 48, the [FeCoNi/Cu] multilayer showed a strong [111] texture as that for x = 38; however, the observed ΔR/R and antiparallel IEC for x = 48 were much smaller than those for x = 38. Detailed microstructural and chemical analyses by scanning transmission electron microscopy revealed that the fluctuation of the thickness of the Cu spacer layer can explain the reduction of antiparallel IEC that gave rise to the decrease in ΔR/R in the case of x = 48. We also discuss the effect of IEC energies on the sensitivity of GMR sensors.