Superconducting proximity effects in YBa$_{2}$Cu$_{3}$O$_{7}$/[Co/Pt] multilayers*

We have studied the penetration of superconducting correlations into Co/Pt multilayers and single Pt thin films deposited on top of c-axis YBa$_{2}$Cu$_{3}$O$_{7}$. We used tunneling conductance measurements across an AlO$_{\mathrm{x}}$ barrier in order to track changes in the electron density of states of the Co/Pt (or Pt) films. A large number of junctions were studied, varying several parameters. We found more pronounced, longer-ranged signatures of proximity-induced superconductivity (energy-gap below T$_{\mathrm{C}})$ in Co/Pt than in single Pt films. This is interpreted by considering a series of magnetic effects specific to the Co/Pt interface, which induce inhomogeneities in the exchange field felt by the conduction electrons and explain the presence of long-range proximity effects.