Magnetic Structure of Ce(Mn$_{1-x}$Cu$_{x})_{2}$Si$_{2}$

The magnetic structure of the Ce(Mn$_{1-x}$Cu$_{x})_{2}$Si$_{2}$ (0 $\le $ x $\le $ 1) series, which evolves from a non-magnetic Kondo-heavy-fermion system at $x$=1 to a 3d-antiferromagnetically ordered mixed valence system at $x$=0, has been studied by both temperature and field dependent magnetization ($M)$ measurements using a SQUID magnetometer. Data were taken in both zero-field-cooled (ZFC) and field cooled (FC) processes. It is found that for 0 $\le x <$ 0.4, Neel temperature decreases rapidly with the increase of the Cu concentration $x$. In the range of $x$ from 0.4 $\le $ x $<$ 0.8, ferromagnetic phase is observed below 150 K, and both the ordering temperature $T_{c}$ and Qurie-Weiss $\theta $ decrease with the increase of $x$ . For $x \ge $ 0.8, the $M$ (T) curves are reversible and display paramagnetic behavior. Thus, the system is non-magnetic as it approaches heavy-fermion compound CeCu$_{2}$Si$_{2}$. A magnetic phase diagram is proposed for this compound series.