Abstract: Due to the proximity of CeCu2Si2 to a quantum critical point, the ground state of this compound is extremely sensitive to sample preparation conditions. Small excess of one component can lead to magnetic or superconducting behaviors. We found that in the alloy CeCu2(Si1-xGex)(2) a small excess of Ge enhances the homogeneity range allowing a precise investigation of stoichiometric effects on the physical properties. In this system, Ge doping produces an increment of the antiferromagnetic transition temperature T-N, while the superconducting one decreases. Particularly, it was found that at x = 0.1 both phases coexist at low temperature. In order to investigate the stability of these phases against changes of the Ce-ligands composition, we prepared a series of CeCu2+y(Si0.9Ge0.1)2-x, samples (0less than or equal toyless than or equal to0.10) and investigated their specific heat and electrical resistivity. We observed that the substitution of Si/Ge by Cu increases the characteristic temperature and weakens the magnetic contribution without modifying TN. A further transition, of the first order character, is observed at lower temperature. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: The evolution of the behavior of the Ce 4f electron with the Cu content in the alloy Ce(Pd1-xCux)(2)Si-2 was investigated by determining its structural, magnetic, transport, and thermal properties. Results obtained on 15 samples with compositions distributed along the whole concentration range allow us to draw a magnetic phase diagram showing three distinct regions. The first region at low Cu concentrations corresponds to the antiferromagnetic-ordered regime. The fast suppression of this magnetic order between x = 0.2 and x = 0.25 suggests the presence of a critical point which separates this region from the second one at larger.x values where no magnetic order is observed. The main characteristic of this second region, which extends up to x = 0.7, is a pronounced increase of the Kondo temperature T-K, from T-K approximate to 15 K at x = 0.25 to T-K approximate to 50 K at x = 0.7. This is in contrast with the fast decrease of T-K in the region with x > 0.7. In this region a small anomaly with a ferromagnetic character is observed in the specific hear arround 4 K. The change in the evolution of T-K with x coincides with a change in the composition dependence of the c lattice parameter of the tetragonal structure, pointing to a structure-related origin of this unusual T-K(x) behavior. This nonmonotonous T-K(x) dependence is reproduced using local-density-approximation band-structure calculations, which show a maximum of the hybridization strength between conduction electrons and Ce 4f stares for intermediate Cu concentrations. Such a T-K(x) dependence which contradicts the monotonous dependence observed in all other Ce-based alloy systems is the hallmark of the Ce(Pd1-xCux)(2)Si-2 alloy, which cannot be described as a Fermi-Liquid system in the nonmagnetic region. [S0163-1829(98)02118-3].

Abstract: We report magnetoelastic studies in the CeCo1−xFexSi alloys. Iron doping has a profound effect on the low temperature linear magnetostriction. At T = 2 K, the strength of the magnetostriction peaks at x = 0.23 where it reaches a value as large as $\[\frac{{\Delta L}}{L} = 3 \times {10^{ – 3}}\]$ in an applied magnetic field B = 16 T. This Fe concentration corresponds to the critical one xc above which long-range antiferromagnetic order is no longer observed. The progressive increment of the hibridization between the Ce 4f orbital and the conduction band, as the magnetic order vanishes, gives rise to a sizeable valence susceptibility that can be finely tuned by the magnetic field explaining the large magnetostrictive effect around xc. At higher x, the magnetostriction decreases, in agreement with a weaker valence susceptibility resulting from a stronger hibridization.

Abstract: A recent study of CeTiGe identified this compound as a paramagnetic heavy Fermion system where the full J = 5/2 multiplet is involved in the formation of the ground state. Here we present a preliminary investigation of the dc-magnetization M_dc(H) and of the magnetoresistance ρ(H) of polycrystalline CeTiGe samples in applied magnetic fields up to μ₀H = 14 T. The results reveal a pronounced metamagnetic transition at a critical field μ₀H_c ≈ 13.5 T at low temperatures, with a step like increase in M_dc(H) of at least 0.6 μ_B/Ce. The metamagnetic transition leads to a strong decrease in ρ(H). A clear hysteresis in M_dc(H) and ρ(H) indicate that in CeTiGe these metamagnetic features correspond to a true thermodynamic, first order type transition in contrast to the critical behavior observed in the canonical system CeRu₂Si₂. Measurements at higher temperatures showed a continuous suppression of the metamagnetic transition with increasing T, which vanishes at T ∼ 30 K. © 2010 IOP Publishing Ltd.

Abstract: Chiral materials, where no improper symmetry operations such as inversion are resent, are systems prone to the appearance of a skyrmion lattice. Recently it has been shown theoretically that not only ferromagnets (FMs) but also antiferromagnets (AFMs) can host such kind of phases. In this work we study a new candidate for AFM skyrmions, EuIr2P2, by means of magnetization and specific heat measurements on poly and single crystals. X-ray diffraction confirms a trigonal chiral crystal structure, where europium ions form helices along the c direction. In spite of predominantly FM interactions, Eu2+ ions order antiferromagnetically at
TN1=5 K in what seems to be an incommensurate amplitude-modulated magnetic state where the moments are oriented mainly along the c direction. A second magnetic transition takes place at TN2=2.9 K, involving the ordering of an in-plane component of the Eu moment likely resulting in an equal-moment structure. Specific heat data show a tail above TN1. Accordingly the magnetic entropy at
TN1 is strongly reduced in comparison to the expected Rln8 value. This evidences a significant amount of frustration. A simple analysis based on a Heisenberg model indicates that the observed properties imply the presence of several relevant interactions, with competing FM and AFM ones resulting in frustration. Thus
EuIr2P2 is a new interesting magnetic system, where chirality and frustration might result in unconventional magnetic textures.