Structural chemistry, magnetic properties and electrical resistivity of the ternary germanides R2RuGe2 (R = Y, La-Nd, Gd-Er)

We have investigated the magnetic properties (magnetization, DC and AC susceptibility) of a new series of ternary rare-earth ruthenium germanides R2RuGe2, which crystallize in the monoclinic structure type Sc2CoSi2 (space group C2/m, No. 12). The two compounds containing yttrium or lanthanum are Pauli-type paramagnets. All the remaining compounds undergo ferromagnetic transitions, except Gd2RuGe2 and Tb2RuGe2, which seem to possess an antiferromagnetic ground state. The former finally exhibits a metamagnetic transition above 2T and the latter, however, proves to be a highly anisotropic narrow domain wall ferromagnet, the critical field being close to 3T. In the paramagnetic region the effective moments deduced are comparable with the ideal tripositive R3+ ion moments and the theta(p) values are generally positive. The temperature dependence of the electrical resistivity is metallic like and reveals pronounced changes of slope near the ordering temperatures. The maxima of the d rho/dT versus T plots are in agreement with the magnetic data (T-ord). The resistivity of Ce2RuGe2 was found to be determined by an interplay of Kondo scattering and crystal-field effects. The temperature dependence of the spin disorder resistivity in the paramagnetic regime for the remaining samples could be attributed to the influence of the crystalline field split 4f levels. Not knowing the exact level schemes, we use a single spacing (delta) crystal-field model for an order of magnitude estimate. (C) 2000 Elsevier Science B.V. All rights reserved.