Magnetism in Pt/Co/Cu multilayers: dependence on Co thickness and the influence of additional superconducting Nb layers

Abstract We report sputtered [Pt/Co( d Co )/Cu] ×15 multilayers and their integration with superconducting Nb. Tuning the Co thickness d Co = 0.6–1.2 nm transforms nearly square perpendicular hysteresis into wasp-waisted switching, while room-temperature magnetic force microscopy (MFM) shows a progression from sparse to dense worm-like domains. Hall measurements on the d Co = 1.2 nm stack reveal an antisymmetric excess Hall signal, obtained after subtracting the ordinary and anomalous components. Incorporating Nb layers of thickness 20 and 60 nm beneath the magnetic multilayer preserves wasp-waisted loops and MFM contrast, whereas a layer of 120 nm modifies the hysteresis loop. A 60 nm Nb layer above the magnetic multilayer reduces the MFM contrast. In low temperature magnetic field dependent MFM imaging, a progression from worm-like to isolated skyrmion-like domains is observed on the application of perpendicular field. Nb–[Pt/Co/Cu] ×15 heterostructures exhibit the expected suppression of T c with decreasing Nb thickness, with an additional reduction relative to single-layer Nb films. These results provide practical design rules, particularly layer order and Nb thickness, for integrating conventional superconductivity with magnetic multilayers.