  A series of Co_xCu_{100-x} (x = 0, 40...75, 100) layers with thicknesses
in-between 13 nm and 55 nm were prepared on silicon substrates using cross-beam
pulsed laser deposition. Wide-angle X-ray diffraction (WAXRD), transmission
electron microscopy (TEM) and electrical transport measurements revealed a
structure consisting of decomposed cobalt and copper grains with grain sizes of
about 10 nm. The influence of cobalt content and layer thickness on the grain
size is discussed. Electron diffraction (ED) indicates the presence of an
intermetallic Co-Cu phase of Cu3Au structure-type. Thermal treatment at
temperatures between 525 K and 750 K results in the progressive decomposition
of Co and Cu, with an increase of the grain sizes up to about 100 nm. This is
tunable by controlling the temperature and duration of the anneal, and is
directly observable in WAXRD patterns and TEM images. A careful analysis of
grain size and the coherence length of the radiation used allows for an
accurate interpretation of the X-ray diffraction patterns, by taking into
account coherent and non-coherent scattering. The alloy films show a giant
magnetoresistance of 1...2.3 % with the maximum obtained after annealing at
around 725 K.
