  We have deposited Co films on the GaAs(001) surface by using an e-beam
evaporation method. The thicknesses of the Co films are measured by using x-ray
reflectivity and Rutherford backscattering. The magnetic properties of the
films have been measured using superconducting quantum interference device. The
magnetization of the films was found to decrease with increasing film
thickness. The slight degradation of magnetic properties is attributed to
increasing roughness on the Co surface or the Co/GaAs interface during the Co
deposition.
