Dependence of magnetism on hybridization in Ce(Cu_1−xNi_x)₂Ge₂

Measurements of specific heat (0.3 K < T < 15 K, P < 1.2 GPa) and electrical resistance (1.2 K < T < 300 K, P < 2 GPa) under hydrostatic pressure on the heavy-fermion system Ce(Cu1−x)2Ge2 (x ⩽ 0.1) were performed to discriminate between effects of chemical substitution and purely steric effects of the 4f-ligand hybridization in Kondo-lattice systems. The latter is effective in forming heavy-mass quasiparticles or generating heavy-fermion band magnetism (HFBM). We find the Kondo temperature TK to be governed by volume, while magnetic-ordering transitions at TNIL and TNIL for 0 < x ⩽ 0.1 cannot be reproduced in CeCu2Ge2 by a corresponding change in volume. Entropy calculations lead us to conclude that the lower transition (TNIL) reflects a reorientation of the magnetic moments within the antiferromagnetically ordered phase and may be a precursor of a HFBM state. Its absolute value critically depends on ligand periodicity and/or density-of-states effects