Geometry and pairing-symmetry effects in superconductor/half-metallic ferromagnet vertical junctions*

The interactions between superconductors (S) and ferromagnets (F) are widely studied nowadays due to the possibility of obtaining equal-spin triplet pairing, which is immune to the exchange field and therefore can propagate over long distances into the F. This effect has fundamental interest as well as a potential for spintronic applications. In this context, we study vertical S/F/S junctions made of a half-metallic F (La_0.7Sr_0.3MnO₃ or La_0.7Ca_0.3MnO₃) with either a d-wave S (YBa₂Cu₃O₇) or a s-wave one (Mo₈₀Si₂₀), aiming to understand to role of the pairing symmetry on the proximity effect and, particularly, on the generation of equal-spin triplet correlations. We will compare low-temperature magneto-transport measurements made in vertical micro-junctions having different geometries, namely three-probe vs. a novel four-probe junction scheme, which is designed to separate conductance features linked to the top electrode’s contact resistance from effects due to transport across the entire S/F/S junction.