Electrical resistivity and magnetic properties of the ternary compounds Ho2TGe2;: T = Ru, Os

We have performed an investigation of the magnetic properties of the new compounds Ho-2(Ru,Os)Ge-2, which crystallize in the monoclinic structure-type Sc2CoSi2 (space-group B2/m), using an AC susceptometer. Both compounds undergo possibly antiferromagnetic transitions at T-N approximate to 40 K; subsequent spin-reorientations towards a ferromagnetic spin alignment occur at temperatures below 20 K. From isothermal (T = 5 K) magnetization measurements versus external field (mu(0)H = 0-3 T) an ordered moment of 5.2 p, has been derived for both samples. In the paramagnetic region effective moments close to the ideal free Ho3+ ion moment (mu(eff) = 10.6 mu(B)) were deduced, the theta(p) values being positive. The temperature dependence of the electrical resistivity reveals pronounced changes of slope at the ordering temperatures T-N and T-C. The maxima of dp/dT versus T are in agreement with magnetic data above. For the paramagnetic region a deflection of the generally linear p-T plot of nonmagnetic metallic systems is observed, which could be attributed to the influence of the crystalline Geld split levels of the seventeenfold degenerate Ho3+ ground-state I-5(8). Not knowing the exact 4-f level scheme, we use a single spacing (delta) crystal-field model for an order of magnitude estimate. The results of the negative magnetoresistivity data are due to the reduced spin disorder scattering in the ordered state. (C) 1998 Elsevier Science B.V. All rights reserved.