0000000000014519
AUTHOR
A. Krimmel
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.
Neutron-scattering studies on CeM2Ge2(M=Ag, Au, and Ru)
The results of elastic, quasielastic, and inelastic neutron-scattering studies on polycrystalline CeM 2 Ge 2 (M=Ag, Au, and Ru) are presented. All compounds reveal long-range magnetic order at low temperatures. Ferromagnetic (M=Ru), antiferromagnetic (M=Au), and incommensurate (M=Ag) structures were detected. Using time-of-flight (TOF) techniques, the crystalline electric-field splittings were determined. With high-resolution TOF experiments the temperature and wave-vector dependence of the magnetic relaxation rate was studied
Alloying experiments on heavy fermion compounds
Abstract This paper is intended to demonstrate the usefulness of controlled alloying for the understanding of heavy-fermion physics: (1) Th-substitution for Ce in CeCu2Si2 emphasizes the dominating role of the dopant-induced strain fields in generating incoherent scattering and pair breaking, (2) replacement of Cu by Ni in Ce(Cu1-xNix)2Ge2 leads to phenomena which are interpreted as derived from a transition between local-moment and itinerant heavy-fermion magnetism, and (3) increasing Cu concentration in UCu4+xAl8-x is accompanied by an antiferromagnetic to nonmagnetic transition near xcr = 1.5 similar to what has been found before for several Ce-based systems. A heavy Fermi-liquid phase w…
Magnetic phase diagrams in heavy-fermion compounds
Magnetic phase diagrams have been explored in heavy-fermion (HF) compounds by controlled changes of the stoichiometry (UCu4+xAl8−x), dopant concentration (Ce(Cu1−xNix)2Ge2) and magnetic field (CeCu2Si2). The results demonstr competition (i) between Kondo and RKKY interactions in the former two compounds and (ii) between HF superconductivity and some cooperative state, presumably HF band magnetism, in the latter.
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…
Magnetic order in the heavy fermion system Ce(Cu1−xNix)2Ge2
Abstract The magnetic phase diagram of the heavy fermion (HF) systems Ce(Cu 1−x Ni x ) 2 Ge 2 is discussed utilizing results of transport, thermodynamic and neutron-scattering measurements. While the Kondo temperature increases monotonically with x, a complex x-dependence is found for the Neel temperature, associated with a transition from local-moment to itinerant HF magnetism.
Neutron diffraction experiments on UCu4+xAl8−x
Abstract Neutron diffraction experiments are reported on UCu4+xAl8−x for concentrations 0.1≤ x ≤1.9 and temperatures 1.6 K≤T≤300 K. For x ≤ 1 these compounds undergo antiferromagnetic phase transitions into a collinear AF I-type structure. with the magnetic moments aligned along the tetragonal c-axis and alternating order within the a−b planes. With increasing concentration the ordering temperatures decrease and moment compensation due to a Kondo-type interaction develops for x>1.
Magnetic order in UCu4+xAl8−x
Abstract A neutron diffraction study has been performed on UCu4+xAl8−x. The compound was chosen as an example of a uranium-based system, which goes from a magnetically ordered state to a pure heavy-fermion state. In the range x = 0.25–1, UCu4+xAl8−x orders in a simple collinear antiferromagnetic structure. With increasing concentration of Cu, the ordering temperature decreases and moment compensation develops due to the increasing hybridization of the 5f electrons.