  We report the results of magnetic measurements for the solid solution
Ce$_2$Au$_{1-x}$Co$_x$Si$_3$. The results reveal that this solid solution is
characterized by a magnetic phase diagram (plot of magnetic transition
temperature versus $x$) unusual for Kondo lattices. In particular, the
spin-glass freezing induced by disorder is observed only for the compositions
at the weak coupling limit; as one approaches the quantum critical point by a
gradual replacement of Au by Co, this disorder effect is surprisingly
suppressed in favor of long range antiferro-magnetic ordering in contrast to
expectations. This unusual interplay between disorder, spin-glass freezing and
the Kondo-effect calls for further refinement of theories on competition
between magnetism and the Kondo effect.
