Angular dependence of superconductivity in superconductor/spin-valve heterostructures

Abstract

We report measurements of the superconducting transition temperature, ${T}_{c}$, in CoO/Co/Cu/Co/Nb multilayers as a function of the angle $\ensuremath{\alpha}$ between the magnetic moments of the Co layers. Our measurements reveal that ${T}_{c}(\ensuremath{\alpha})$ is a nonmonotonic function, with a minimum near $\ensuremath{\alpha}=\ensuremath{\pi}/2$. Numerical self-consistent solutions of the Bogoliubov--de Gennes equations quantitatively and accurately describe the behavior of ${T}_{c}$ as a function of $\ensuremath{\alpha}$ and layer thicknesses in these superconductor/spin-valve heterostructures. We show that experimental data and theoretical evidence agree in relating ${T}_{c}(\ensuremath{\alpha})$ to enhanced penetration of the triplet component of the condensate into the Co/Cu/Co spin valve in the maximally noncollinear magnetic configuration.