  We studied the magnetic properties of La$_{0.7}$Ca$_{0.3}$MnO$_3$ /
YBa$_2$Cu$_3$O$_{7-\delta}$ superlattices. Magnetometry showed that with
increasing YBa$_2$Cu$_3$O$_{7-\delta}$ layer thickness the saturation
magnetization per La$_{0.7}$Ca$_{0.3}$MnO$_3$ layer decreases. From polarized
neutron reflectometry we determined that this magnetization reduction is due to
an inhomogenous magnetization depth profile arising from the suppression of
magnetization near the La$_{0.7}$Ca$_{0.3}$MnO$_3$ /
YBa$_2$Cu$_3$O$_{7-\delta}$ interface. Electron energy loss spectroscopy
indicates an increased 3d band occupation of the Mn atoms in the
La$_{0.7}$Ca$_{0.3}$MnO$_3$ layers at the interface. Thus, the suppression of
ferromagnetic order at the La$_{0.7}$Ca$_{0.3}$MnO$_3$ /
YBa$_2$Cu$_3$O$_{7-\delta}$ interface is most likely due to charge transfer
between the two materials.
