Triplet generation and upper critical field in superconducting spin valves based onCrO2

Abstract

It has been recently reported that a superconducting triplet spin valve (TSV) based on the half-metallic ${\mathrm{CrO}}_{2}$ can show ``colossal'' variations of the critical temperature, up to more than 1 K. This can be achieved when the magnetic noncollinearity between the mixer $({\text{F}}_{1})$ and the drainage ferromagnetic layer (F) is maximized. In this work we investigate further such TSV devices looking at two aspects: first, we present the dependence of the TSV effect on the thickness of the mixer layer; second, we look at the perpendicular upper critical field ${H}_{c2\ensuremath{\perp}}$ as a function of the temperature. The thickness dependence, which is nonmonotonic as expected, represents a further proof that the effect is due to the generation of equal-spin triplet Cooper pairs, while what we observe for the ${H}_{c2\ensuremath{\perp}}$ versus $T$ curves is an interesting and peculiar behavior: there is a clear deviation from the universal linear dependence and the average slope is suppressed much more than what can be described with the formalism used for conventional proximized structures.