Nb and Nb/Co films: Testing a new approach to determine the Co stray field and its influence on superconducting properties

Anisotropic Ginzburg-Landau model was systematically tested in NbtNb and NbtNb/Cu5nm/Co40nm (tNb = 20 and 100 nm) films. A ΔTC-parameter was defined as a temperature difference between the critical temperatures determined for in-plane and out-of-film plane field configurations (ΔTC=TC⊥C−TC∥C). The ΔTC behavior for Nb(20 nm) and Nb(20 nm)/Co(40 nm) films shows a linear increase with applied field concomitantly with the increase of magnetization values in the out-of-film plane configuration. The stray field of ferromagnetic Co layer was determined in the zero field case to be (7 ± 2) mT, while a variation ratio between the stray field and the applied field ((dBCodB) of the Co layer was calculated to be (−0.22 ± 0.02). Our results bring contributions to clarify proximity and magnetostatic effects; issues that still need to be comprehended for superconducting spin valve technological applications.