Unanticipated proximity behavior in ferromagnet-superconductor heterostructures with controlled magnetic noncollinearity
L. Y. Zhu, Yaohua Liu, F. S. Bergeret, J. E. Pearson, S. G. E. te Velthuis, S. D. Bader, and J. S. Jiang
Accepted
Magnetization non-collinearity in ferromagnet (F)/superconductor (S) heterostructures is expected to enhance the superconducting transition temperature (Tc) according to the domainwall superconductivity theory, or to suppress Tc when spin-triplet Cooper pairs are explicitly considered. We study the proximity effect in F/S structures where the F-layer is a Sm-Co/Py exchange-spring bilayer and the S-layer is Nb. The exchange-spring contains a single, controllable and quantifiable domain wall in the Py layer. We observe an enhancement of superconductivity that is non-monotonic as the Py domain wall is increasingly twisted via rotating a magnetic field, different from theoretical predictions. We have excluded magnetic fields and vortex motion as the source of the non-monotonic behavior. This unanticipated proximity behavior suggests that new physics is yet to be captured in the theoretical treatments of F/S systems containing non-collinear magnetization.