0000000000181535
AUTHOR
A. Grauel
LOCAL-MOMENT AND ITINERANT ANTIFERROMAGNETISM IN THE HEAVY-FERMION SYSTEM CE(CU1-XNIX)2GE2
Elastic and inelastic neutron-scattering studies on the system Ce(Cu1−xNix)2Ge2 are reported. These measurements are complemented by measurements of the magnetic susceptibility, high-field magnetization, heat capacity, thermal expansion, electrical resistivity and thermopower. The results reveal an interesting T-x phase diagram consisting of two different antiferromagnetic phases for x 0.5. Further experimental evidence for different types of antiferromagnetic ordering derives from a line-shape analysis of the quasielastic neutron-scattering intensity, from magnetization and thermopower experiments.
Instabilities in heavy-fermion systems
Abstract We review (i) an itinerant antiferromagnetic phase transition below 4 K in Ni-rich Ce(Cu 1− x Ni x ) 2 Ge 2 systems, (ii) the coincidence at T = 0.63 K of both a structural lattice instability in “as-grown” (non-superconducting) CeCu 2 Si 2 single crystals and bulk superconductivity in annealed ones as well as (iii) antiferromagnetic and superconducting transitions at T N = 4.6 K and T c = 1 K, respectively, in the heavy-fermion compound UNi 2 Al 3 .
Neutron diffraction study of the heavy fermion superconductors UM2Al3(M=Pd, Ni)
An elastic neutron scattering study was performed on the new superconducting heavy fermion systems UPd2Al3 and UNi2Al3. The neutron diffraction patterns reveal unambiguously long range antiferromagnetic order in UPd2Al3 with an ordered magnetic momentμ U = (0.85±0.03)μ B , which coexists with the superconducting state. This is by far the largestμ U value observed for any heavy fermion superconductor. For UNi2Al3, no long-range magnetic order could be observed for temperaturesT≧1.5 K, yielding an upper limit of the ordered moment of 0.2μ B .
Alloying-induced transition from local-moment to itinerant heavy fermion magnetism in Ce(Cu1−xNix)2Ge2
Abstract A monotonous increase of the Kondo temperature in Ce(Cu1−xNix)2Ge2 from 7 (x = 0) to 30 K (x = 1) is accompanied by drastic changes of ground state properties: for x⩽0.2, a modulated magnetic structure (q01 = (0.28, 0.28, 0.54)) involving Kondo-reduced local Ce moments ( μ s = 0.74μ B Ce for x = 0) forms below TN1(x). TN1 = 4. 1 K for CeCu2Ge2 is strongly depressed upon increasing x. At x ≲ 0.2, a different modulation develops below TN2(x) which becomes maximum (≃4 K) for x = 0.5. Since this is characterized by a very small value of q02 (=(0, 0, 0.13) at x = 0.5) and a gradually decreasing ordered moment (reaching μs ≲ 0.2μB/Ce for x ⩾0.65), we ascribe it to “heavy fermion band mag…