Antiferromagnetic Kondo-lattice systems Ce2Rh3Ge5 and Ce2Ir3Ge5 with moderate heavy-fermion behavior

The results of electrical resistivity, magnetic susceptibility, specific heat, isothermal magnetization, and magnetoresistance measurements on Ce2Rh3Ge5 and Ce2Ir3Ge5 are reported. For both systems, the magnetic contribution to the resistivity shows the logarithmic T dependence in two separate T ranges being typical of a Kondo-lattice system in the presence of crystalline field. A marked peak in the susceptibility and a sharp drop in the resistivity are observed at T-N = 5.5 and 9.5 K for Ce2Rh3Ge5 and Ce2Ir3Ge5, respectively. The total drop in resistivity is as large as 300 mu Omega cm. Isothermal magnetization curves at 1.3 K reveal a field induced transition at 23 T in Ce2Rh3Ge5 and two transitions at 10 and 15 T in Ce2Ir3Ge5 The saturation moment of 0.8 beta(B)/Ce is suggestive of the Gamma(7) doublet ground state in both compounds. The specific heat exhibits a lambda-type anomaly around T-N, while the values of magnetic entropy at T-N are reduced to 50 and 65% of R ln 2 for Ce2Rh3Ge5 and Ce2Ir3Ge5, respectively. The linear coefficients of specific heat are 148 and 152 mJ/K-2 mol Ce above T-N. Thus both compounds are classified into moderate heavy-fermion antiferromagnets. [S0163-1829(99)02538-2].