Crystal-field effects in the mixed-valence compoundsYb2M3Ga9(M=

Abstract

Magnetic susceptibility, heat capacity, and electrical resistivity measurements have been carried out on single crystals of the intermediate valence compounds Yb2Rh3Ga9 and Yb2Ir3Ga9. These measurements reveal a large anisotropy due apparently to an interplay between crystalline electric field (CEF) and Kondo effects. The temperature dependence of magnetic susceptibility can be modelled using the Anderson impurity model including CEF within an approach based on the NonCrossing Approximation.PACS numbers: 75.30.Mb,75.20.Hr,71.27.+a,71.28.+d The intermediate valence compounds pose one of the most challenging problems of strongly correlated electron systems. Different ingredients contribute to the complexity of these fascinating systems: the presence of strong Kondo interactions, the level structure of the crystal electric field (CEF) f -orbitals, the different hybridizations between each level and the conduction band, and the eventual coherence effects and magnetic interactions introduced by the periodicity of the Kondo lattice. 1Strong valence fluctuations are observed in the intermetallic compounds with Ce, Yb and U. In particular, Yb compounds attract a great deal of interest because the trivalent Yb ion is at least in some sense the hole counterpart of the Ce 3+ ion which has one electron in its 4f shell. As in the case of the Ce compounds, 2 the Ybbased intermetallics exhibit a diversity of physical properties that remain to be understood. 3The isostructural series of compounds R 2 M 3 X 9 (R = La, Ce, Yb, U; M=Co, Rh, Ir; X = Al, Ga) exhibit antiferromagnetic ordering for R=Yb, X=Al, and mixedvalence behavior for R=Ce,Yb and X=Ga. 4,5,6,7 All the U-based compounds order antiferromagnetically at temperatures below 40 K.4 The Yb 2 M 3 Ga 9 compounds are a suitable class of materials for studying the difference in the electronic structure between the magnetically ordered Kondo lattice and the mixed-valence systems. The orientation-dependent temperature T max of the maximum in the magnetic susceptibility suggests the possibility of an anisotropic Kondo effect.8,9 Previously, Petrovic et al. studied ternary R-Ir-Ga compounds (R=rare earth) that were assigned the RIr 2 Ga stoichiometry in their work. 10,11,12 Elemental analysis studies unavailable to these previous authors suggest that R 2 Ir 3 Ga 9 is the correct stoichiometry of these materials instead. The R 2 Ir 3 Ga 9 compounds with Ce and Yb show reduced magnetic moments and the absence of magnetic order above 0.04 K. 11The thermodynamic properties of the single-impurity model have been calculated exactly using the Betheansatz technique, 14,15,16,17,18 and also approximately within the Non-Crossing Approximation (NCA), which shows good agreement with the former.19 However, to the best of our knowledge, it has always been assumed that the hybridization V m between any state of the magnetic configuration |m and the conduction electrons is independent of m even when the CEF is included.14,15,16 This is a requirement for the integrability of the problem; 20 a...

Anisotropic intermediate valence in Yb2Rh3Ga9

“…From the Lorentzian fits it is possible to extract the static susceptibility. Good agreement (Table 1) is found at all temperatures, except at 12 K where it appears that the INS response is not sensitive to the low temperature upturn (which is probably extrinsic) observed in the static susceptibility [1]. This agreement gives confidence in our determination of S mag .…”

“…Recently, we have established that Yb 2 Rh 3 Ga 9 is an anisotropic intermediate valence (IV) system [1,2]. In these studies, we found that Anderson impurity model (AIM) calculations, including the effects of crystal field (CF) level splitting, were able to simultaneously reproduce the temperature dependence of the magnetic susceptibility and the 12 K inelastic neutron scattering spectrum (INS).…”

Nonequilibrium magnetotransport through a quantum dot: An interpolative perturbative approach

“…[21] Also a Kondo model has been solved exactly for particular parameters. [22] The non-crossing approximation (NCA), which has been successfully used to calculate thermodynamic properties of generalized Anderson models above or near the Kondo temperature T K , [23][24][25] has also been used for nonequilibrium situations. [26][27][28] Unfortunately, at low temperatures this method fails to fulfill Fermi liquid relations in the equilibrium case, [29] and the spectral density presents a spurious peak at the Fermi level in the presence of a magnetic field B.…”

Ordering temperature and thermodynamic properties of Kondo systems

“…In spite of these limitations related with lattice effects, our approach was successful to describe magnetic susceptibility and specific heat of Yb compounds in the non-magnetic phase [8,9]. We believe that it can also be used inside the magnetic phase, leading naturally to small magnetic moments as a consequence of the saturation of…”

“…This points to a strong AF interaction 1 between the Yb ions. However, the system does not order due to the dominance of the single ion is necessary for a quantitative agreement with experiment [9]. Here we describe the general formalism.…”