UC Irvine

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 Néel temperatures TN between 0.5 and 4.2 K. Just above TN, all these materials have a significant enhancement of their electronic specific heat, which can be as large as 3-4 J/molK2. 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 TN and the Kondo temperature TK 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 TN in CeIr2Sn2 were performed to explore this competition, which is discussed in terms of Doniach's Kondo-necklace model. © 1991 The American Physical Society.