  The existence of coherent magnetic correlations in the normal phase of
cuprate high-temperature superconductors has proven difficult to measure
directly. Here we report on a study of ferromagnetic-superconductor bilayers of
La2/3Ca1/3MnO3/YBa2Cu3O7 (LCMO/YBCO) with varying YBCO layer thicknesses. Using
x-ray magnetic circular dichroism, we demonstrate that the ferromagnetic layer
induces a Cu magnetic moment in the adjacent high-temperature superconductor.
For thin samples, this moment exists at all temperatures below the Curie
temperature of the LCMO layer. However, for a YBCO layer thicker than 12 unit
cells, the Cu moment is suppressed for temperatures above the superconducting
transition, suggesting this to be a direct measurement of magnetic coherence in
the normal state of a superconducting oxide.
