Signature of a crossed Andreev reflection effect in the magnetic response of YBa2Cu3O7-δ junctions with the itinerant ferromagnet SrRuO3 -: art. no. 184515

The magnetic properties of superconducting-ferromagnetic-superconducting (SFS) and SF ramp-type junctions with YBa2Cu3O7-delta (YBCO) electrodes (S) and the itinerant ferromagnet SrRuO3 (SRO-F), were investigated. We looked for a crossed Andreev reflection effect (CARE) in which an electron from one magnetic domain in F is Andreev reflected as a hole into an adjacent, oppositely polarized, domain while a pair is transmitted into S. The CARE is possible in SRO since the width of its domain walls is of the order of the YBCO coherence length (2-3 nm). Our junctions behave as typical magnetic tunneling junctions, as the conductance spectra were always asymmetric and a few showed bound-state peaks at finite bias that shifted with field according to classical Tedrow-Meservey theory. In many of our SFS junctions with a barrier thickness of 10-20 nm, a prominent zero-bias conductance peak (ZBCP) has been observed. This peak was found to decrease linearly with magnetic field, as expected for Andreev and CARE scattering. In contrast, in SF junctions, the observed ZBCP was found to decrease versus field almost exponentially, in agreement with the Anderson-Appelbaum theory of scattering by magnetic states in F. Thus, transport in our SFS and SF junctions depends strongly on the size of the F layer. We also found that in both cases, the ZBCP height at zero field decreased with increasing magnetic order of the domains in F, in agreement with the CARE mechanism.