Extracting Stray Magnetic Fields from Thin Ferromagnetic Layers in Hybrid Superconducting/Ferromagnetic Heterostructures

Hybrid Nb(20)/Cu(5)/Py(2), Nb(20)/ Cu(5)/ Co(40) and Nb(20)/Cu(d Cu)/Py(2)/Cu(5)/Co(40) heterostructures (values in nanometers and d(Cu) = 0, 2.5 and 5.0) were fabricated using a confocal DC magnetron sputtering setup. Performing magnetotransport measurements and using the anisotropic Ginzburg-Landau approach, the stray field values in zero-applied field (B-0Co, B-0Py and B0Py+Co) were estimated as being -9mT (+31mT) for the hybrid Nb/Cu/Co (Nb/Cu/Py) trilayers and +36mT for the hybrid ordinary Nb/Cu(5)/Py/Cu/Co spin-valve heterostructure. The effective fields acting on the superconducting layer in the hybrid non-ordinary Nb/Cu/Py and Nb/Cu/Co spin-valve heterostructures and its dependence with the applied magnetic field were also quantified, showing that the stray fields of thin ferromagnetic layers are the same order of magnetide but with different strengths. For an applied field of 1 T, the spin-valve effect values of - 230mK (+ 300mK), previously found for the hybrid Nb/Cu/Co (Nb/Cu/Py) trilayers and + 140 mK for the Nb/Cu(5)/Py/Cu/Co heterostructure, had their physical origin better discussed and demonstrated. The 2-nm-thick ferromagnetic Py layer strongly contributes to the effective fields, and the low spin-valve effect of + 140 mK for the ordinary Nb/Cu(5)/Py/Cu/Co spin-valve heterostructure would be a consequence of two contributions of opposite signs governed by the Py and Co layers and also due to the proximity effect contribution.

Automated summary

Hybrid superconducting/ferromagnetic heterostructures were fabricated and analyzed, showing that the stray field values are on the same order of magnitude but with different strengths among the thin ferromagnetic layers. The effective fields acting on the superconducting layer in different structures were quantified, with the 2nm-thick ferromagnetic Py layer playing a significant role in contributing to the effective fields. The spin-valve effect values were discussed and demonstrated to have physical origins related to the contributions of the Py and Co layers and the proximity effect.