Effect of sputtering pressure-induced roughness on the microstructure and the perpendicular giant magnetoresistance of Fe/Cr superlattices

We have studied the connection between structure and magnetism of Fe/Cr superlattices as a function of sputtering pressure. To measure the perpendicular giant magnetoresistance, we have fabricated microstructured Fe/Cr pillars embedded in SiO₂ and interconnected with Nb electrodes. Because of the uniform current distribution in the Nb electrodes and the minimization of the superlattice-electrode contact resistance, the method allows a simple and independent measurement of the perpendicular superlattice resistance and giant magnetoresistance. A detailed quantitative structural analysis by x-ray diffraction, transmission electron microscopy, and high spatial resolution electron-energy-loss spectroscopy imaging, was correlated with magnetization and anisotropic magnetotransport properties. Structural characterization of [Fe(3nm)/Cr(1.3nm)]₂₀ superlattices indicate that the roughness increases monotonically with pressure. The current perpendicular to the plane giant magnetoresistance was also found to increase with pressure. This is interpreted as arising from an enhanced spin-dependent scattering.