Uniaxial magnetic anisotropy in three-bilayer Co/Cu and Co/Al superlattices

Highlights: • Three-bilayer ultrathin Co/Cu and Co/Al superlattices show low coercivity. • Uniaxial magnetic anisotropy was observed in Co/Cu and Co/Al superlattices. • Co/Cu superlattice shows anisotropic magnetoresistance. • Interface roughness and layer thickness of superlattices affect magnetic properties. -- Abstract: We present the magnetic properties of three-bilayer superlattices [Co(0.8 nm)/Cu(1.1 nm)]₃ and Co(0.8 nm)/Al(2.2 nm)]₃ grown by magnetron sputter deposition on SiO₂ substrates. Using the surface magneto-optical Kerr effect we observed longitudinal magnetic hysteresis loops with low coercivity values of < 17 × 10⁻⁴ T and < 7 × 10⁻⁴ T from Co/Cu and Co/Al superlattices, respectively. From the hysteresis loops as a function of in-plane azimuthal angle of the Co/Cu and Co/Al superlattices, we observed an in-plane uniaxial anisotropy in coercivity and squareness. Using a four-point square configuration we observed positive and negative anisotropic magnetoresistances (AMR) with values +0.5% and −0.5% from Co/Cu superlattice depending on whether the applied current is perpendicular or parallel to the applied magnetic field direction, respectively. The surface morphology including vertical root-mean-square roughness and lateral correlation length were examined by atomic force microscopy. The number of bilayers and the thicknesses of Co, Cu and Al in the superlattices were examined by X-ray reflectivity. The observed magnetic properties were correlated to the interface roughness and layer thickness. The low coercivity, low saturation field, near-one squareness, and finite MR value of the three-bilayer Co/Cu superlattice has potential applications in low magnetic field detection and sensors.