COMPETING INTERACTIONS IN THE HEAVY-ELECTRON ANTIFERROMAGNETS CEM2SN2 (M = NI, IR, CU, RH, PD, AND PT)

Specific-heat, magnetic-susceptibility, and resistivity measurements on annealed polycrystalline samples of CeM2Sn2, with M = Ni, Ir, Cu, Rh, Pd, and Pt, indicate that each of these compounds orders antiferromagnetically at Neel temperatures T(N) between approximately 0. 5 and 4.2 K. Just above T(N), all these materials have a significant enhancement of their electronic specific heat, which can be as large as 3-4 J/mol K2. We discuss the role of critical fluctuations on the specific heat and argue that the enhancement is associated with a large effective mass and not fluctuations. The anomalously low ordering temperatures and very large electronic specific heat suggest that T(N) and the Kondo temperature T(K) are comparable, making these materials particularly attractive for studying the competition between Kondo and Ruderman-Kittel-Kasuya-Yosida interactions. Measurements of the pressure dependence of T(N) in CeIr2Sn2 were performed to explore this competition, which is discussed in terms of Doniach's Kondo-necklace model.