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 Ce${\mathit{M}}_2$ ${\mathrm{Sn}}_2$, with M=Ni, Ir, Cu, Rh, Pd, and Pt, indicate that each of these compounds orders antiferromagnetically at Néel temperatures ${\mathit{T}}_{\mathit{N}}$ between ∼0.5 and 4.2 K. Just above ${\mathit{T}}_{\mathit{N}}$, all these materials have a significant enhancement of their electronic specific heat, which can be as large as 3–4 J/${\mathrm{molK}}^2$. 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 ${\mathit{T}}_{\mathit{N}}$ and the Kondo temperature ${\mathit{T}}_{\mathit{K}}$ 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 ${\mathit{T}}_{\mathit{N}}$ in ${\mathrm{CeIr}}_2$ ${\mathrm{Sn}}_2$ were performed to explore this competition, which is discussed in terms of Doniach’s Kondo-necklace model.