EVOLUTION OF MAGNETISM AND SUPERCONDUCTIVITY IN CECU2(SI1-XGEX)(2)

We have determined the magnetic phase diagram of CeCu2(Si1-xGex)(2) us ing specific heat, susceptibility, and resistivity measurements and ad ditional thermal expansion and muon spin resonance experiments. The sy stem evolves continuously from the heavy-fermion state at x = 0 to an antiferromagnetically (AF) ordered state at x = 1, though the magnetic structure undergoes significant modifications. The results strongly s uggest that the AF ordering emerges from the A phase of pure CeCu2Si2. The phase diagram can be divided into three regions: Low Ge content ( x less than or equal to 0.2) leads to an enhancement of the A phase of pure CeCu2Si2 and to a moderate decrease of the Kondo temperature. De spite this increase of the magnetic character, we could observe superc onductivity up to x = 0.1. At large Ge content (x > 0.5) the behavior resembles that of pure CeCu2Ge2. The intermediate region is characteri zed by the appearance of a second magnetic transition below T-N, which seems to be of first-order type. The appearance of this transition le ads to a well-defined critical point at x = 0.3 and suggests the possi bility of another critical point at x = 0.5.