An unusual interplay among disorder, Kondo-effect and spin-glass behavior in the Kondo lattices, Ce${}_2$Au${}_{1-x}$Co${}_x$Si${}_3$

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.