Heavy fermion compounds on the geometrically frustrated Shastry–Sutherland lattice

We present measurements of the basic properties of Ce2Ge2Mg, Yb2Pt2Pb and Ce2Pt2Pb, which are members of a new class of geometrically frustrated magnets R2T2X (R = rare?earth, T = transition?metal, X = main?group). Here, the moment-bearing R atoms are confined to layers where they are arranged in the Shastry?Sutherland lattice. Magnetic susceptibility and specific heat measurements indicate that Ce2Ge2Mg orders antiferromagnetically at 9.4?K and Yb2Pt2Pb at 2.07?K. No long ranged order is observed in Ce2Pt2Pb above 0.05?K. Analysis of Schottky peaks in the specific heat indicates that all three compounds have doublet ground states that are well separated in energy from the excited states of the crystal-field-split manifold. Electrical resistivity measurements show that Ce2Ge2Mg and Yb2Pt2Pb are excellent metals with small residual resistivities. However, the measured resistivity of Ce2Pt2Pb is large and almost temperature-independent, suggesting that strong disorder or perhaps strong quantum critical fluctuations saturate the quasiparticle scattering in this compound. The magnetic entropy develops very slowly above the onset of antiferromagnetic order and we discuss the possibility that a nonordered fluid of dimerized moments exists above TN in Ce2Ge2Mg and Yb2Pt2Pb, and for a wide range of temperatures in Ce2Pt2Pb, which appears to be close to a frustration-driven quantum critical point.