  The structural and magnetic properties of Co$_{18-m}$Cu$_m$ ($0\leq m\leq
18$) clusters are investigated with a genetic algorithm and a $spd$-band model
Hamiltonian in the unrestricted Hartree-Hock approximation respectively. In
general, Cu atoms tend to occupy the surface, while Co atoms prefer to the
interior of the clusters. Layered structures appear in some clusters with given
stoichiometric compositions. The introduction of Cu atoms leads to large
increase of the magnetic moment of Co-rich circumstance and nearly zero
magnetism of the Cu-rich ambient. The interaction between Cu and Co atoms
induces nonzero magnetic moment for Cu atoms. The total magnetic moments tend
to decrease with the increase of Cu atoms. However, some particular large
magnetic moment are found to be closely related to the structures. The
environment of Cu and Co atoms have a dominant effect on the magnetism of the
cluster.
