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Kondo Lattice Models for Rare-Earth and Actinide Systems

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Coqblin B.

Acta Physica Polonica A

2012

vol. 121

issue 5-6

1005-1013

We present here some works on the strong competition between the Kondo effect, magnetic order and eventually spin glass or frustration effect in anomalous rare-earth and actinide systems. First, we develop an underscreened Kondo lattice model with S_{f} = 1 spins for the 5f-electrons and we have recently improved it by deriving, by the Schrieffer-Wolff transformation, a 5f-band with a finite bandwidth. The underscreened Kondo lattice model can account for properties of some uranium and neptunium compounds, like UTe, Np_2PdGa_3 or UCu_2Si_2 which have a large Curie temperature T_{c} of order 100 K and present also a Kondo behavior. In particular, we can account for the observed maximum of T_{c} under pressure in UTe and the magnetization curves of NpNiSi_2 showing the occurrence of the Kondo effect at low temperatures below T_{c}. Second, we have studied the properties of disordered cerium alloys like CeCu_xNi_{1-x} or CeRh_xPd_{1-x} by considering the Kondo effect, a ferromagnetic order and a spin glass behavior described by several approaches. The van Hemmen approach gives a good explanation of the properties of cerium alloys and we are describing the magnetic glass clusters which occur in both spin glass and ferromagnetic phases. Third, we present a new description of a frustrated Kondo lattice model, which can account for the behavior under pressure or doping of some ytterbium compounds like Yb_2Pd_2Sn and YbAgGe.

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1 Acta Physica Polonica A

1 2012

1 Coqblin B.

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Kondo Lattice Models for Rare-Earth and Actinide Systems