Effect of Co-Doping on the Magnetic Ground State of the Heavy-Fermion System CeCu₂Ge₂ Studied by Neutron Diffraction

The antiferromagnetic phase transition of the heavy-fermion system Ce(Cu (Formula presented.) Co (Formula presented.)) (Formula presented.) Ge (Formula presented.) for x = 0.05 and 0.2, showing up in specific heat, magnetic susceptibility, and muon spin relaxation ((Formula presented.) SR) data, has been further investigated. The neutron diffraction (ND) results show that Co-doping drastically reduces the moment size of Ce, without a qualitative change in the magnetic structure of the undoped compound CeCu (Formula presented.) Ge (Formula presented.). An incommensurate magnetic propagation vector k = (0.2852, 0.2852, 0.4495) with a cycloidal magnetic structure with a Ce moment of 0.55 (Formula presented.) in the (Formula presented.) -plane has been observed for x = 0.05. Although for x = 0.2 the specific heat and magnetic susceptibility data reflect a phase transition with a broad peak and the muon relaxation rate shows a sharp peak at T = 0.9 K, our ND data dismiss the possibility of a long-range magnetic ordering down to 50 mK. The ND data, along with previously reported results for x = 0.2, are interpreted in terms of the reduced ordered state magnetic moments of the Ce (Formula presented.) ion by Kondo screening and the presence of dynamical short-range magnetic correlations.