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 Ho2(Ru,Os)Ge2, which crystallize in the monoclinic structure-type Sc2CoSi2 (space-group B2/m), using an AC susceptometer. Both compounds undergo possibly antiferromagnetic transitions at TN∼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 (μ0H=0-3 T) an ordered moment of 5.2 μB has been derived for both samples. In the paramagnetic region effective moments close to the ideal free Ho3+ ion moment (μeff=10.6 μB) were deduced, the θp values being positive. The temperature dependence of the electrical resistivity reveals pronounced changes of slope at the ordering temperatures TN and TC. The maxima of dρ/dT versus T are in agreement with magnetic data above. For the paramagnetic region a deflection of the generally linear ρ-T plot of nonmagnetic metallic systems is observed, which could be attributed to the influence of the crystalline field split levels of the seventeenfold degenerate Ho3+ ground-state 5I8. Not knowing the exact 4-f level scheme, we use a single spacing (δ) 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. (orig.)