LABORATORI NAZIONALI DI LEGNARO
The magnetic (H,T)-phase diagrams of CeCu2Ge2 and CeCu2Ge2 have similar features, although only the latter one becomes superconducting at ambient pressure. In tetragonal CeCu2Ge2 at least three magnetic phases AF1, AF2 and a yet unknown phase IM exist below TN = 4.2 K and in fields up to 35 T. Furthermore, the nature of the phase transition from AF1 to AF2 is discussed controversially in the literature. We present results for fields up to 15 T parallel to the [110] direction of thermodynamic (magnetization, magnetostriction), electrical transport and elastic neutron diffraction measurements. At temperatures below 1 K a first order transition from AF1 to AF2 at around 8 T was found characterized by a change of the propagation vector from q1 = (0.285 0.285 0.538) to q2 = (0.310 0.310 0.543), followed by another slight shift at 10 T to q2mod = (0.317 0.317 0.543). Above 12.5 T the magnetic satellites of type (h h l) have vanished. To interpret the results of macroscopic measurements and existing neutron scattering data a mean-field simulation by the McPhase program was realized, concluding a double-q magnetic structure with q1± = (0.286 ±0.286 0.571) that changes to a single-q structure with q2 = (0.271 0.271 -0.600) at about 8 T. These calculations also reveal the principal shape of magnetization and susceptibility curves published earlier. Finally, the calculated (H,T)-phase diagram agrees satisfactorily to that deduced from experiments. The consistence of experimental results and theoretical model is important for the understanding of magnetism in CeCu2Ge2.

DATA: 10-05-2016