LONG-RANGE MAGNETIC ORDER IN CE(CU1-XAGX)6

In Ce(Cu1-xAgx)6 new results are reported on the electrical resistivity rho(T) (1.3 less-than-or-equal-to T less-than-or-equal-to 300 K) and the lattice parameters at room temperature for x less-than-or-equal-to 0.20, on the heat capacity C(T) (50 mK less-than-or-equal-to T less-than-or-equal-to 4 K) for x = 0.15 and 0.20, and on C(T) (1.5 less-than-or-equal-to T less-than-or-equal-to 20 K) in magnetic fields to 9.8 T for x = 0.1. Sharp anomalies in C(T) for x = 0.15 and 0.20 and in rho(T) for x = 0.20 near the magnetic ordering temperatures determined in earlier susceptibility studies conform the long-range nature of the magnetic transitions in this system. With increasing x the resistivity maximum is shifted to lower temperatures and the lattice expands; it is argued that this volume expansion is primarily responsible for a decrease in the effective Kondo interaction relative to the magnetic exchange interaction between Ce-moments which in turn leads to long-range magnetic order in this system. For x = 0.10 the observed increase in C(T) as a function of magnetic field over the temperature range studied (1.5-20 K) is shown to follow directly from the anticipated behavior of a local-moment system.