  We grow epitaxial Sm-Co thin films by sputter deposition from an alloy target
with a nominal SmCo5 composition on Cr(100)-buffered MgO(100) single-crystal
substrates. By varying the Ar gas pressure, we can change the composition of
the film from a SmCo5-like to a Sm2Co7-like phase. The composition, crystal
structure, morphology and magnetic properties of these films have been
determined using Rutherford Backscattering, X-ray diffraction and magnetization
measurements. We find that the various properties are sensitive to the sputter
background pressure in different ways. In particular, the lattice parameter
changes in a continuous way, the coercive fields vary continuously with a
maximum value of 3.3 T, but the saturation magnetization peaks when the lattice
parameter is close to that of Sm2Co7. Moreover, we find that the Sm content of
the films is higher than expected from the expected stoichiometry.
