Magnetic and transport properties of layered Yb2TGe6 (TÂ =Â Ni, Cu, Pd, Pt)

We report the magnetic and transport properties of Yb2TGe6 (T = Ni, Cu, Pd, Pt) which crystallize in the orthorhombic Ce2CuGe6-type structure. The unit cell volume increases by 6% on going from the compound with T = Ni to that with T = Pt. For T = Ni, the magnetic susceptibility χ has a maximum at 75 K and the thermopower exhibits a minimum of −28 μV/K at 200 K, which are characteristic behaviors of a valence fluctuating Yb compound. The electronic specific heat coefficient γ of 100 mJ/K2 mol-f.u. for T = Ni decreases to 28 mJ/K2 mol-f.u. for T = Pd. The χ(T) for T = Pd and Pt shows very weak temperature dependence. This change from a valence fluctuating state for T = Ni to an enhanced Pauli paramagnetic state for T = Pd and Pt may be caused by the increase of the interatomic distances between the Yb atom and the ligand atoms.