Effect of anisotropy in the S=1 underscreened Kondo lattice

• Published in: Journal of magnetism and magnetic materials Vol. 372; pp. 247 - 252
• Main Authors: Thomas, Christopher, da Rosa Simões, Acirete S., Lacroix, Claudine, Iglesias, José Roberto, Coqblin, Bernard
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.12.2014; Elsevier
• Subjects: Anisotropy; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Crystal lattices; Exact sciences and technology; Ferromagnetism; Kondo effect; Lattices; Magnetic properties and materials; Magnetically ordered materials: other intrinsic properties; Mathematical models; Neptunium; Orbitals; Physics; Strong correlated system; Transformations; Underscreened Kondo effect; Uranium; Valence fluctuation, kondo lattice, and heavy-fermion phenomena; Underscreened Kondo effect; Uranium; Strong correlated system; Anisotropy; Neptunium; Mean field approximation; Curie point; Magnetic ordering; Crystal field; Coexistence; Kondo effect; Reentrant phases; Ferromagnetism; Anderson model; Kondo lattice
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2014.07.028

We study the effect of crystal field anisotropy in the underscreened S=1 Kondo lattice model. Starting from the two orbital Anderson lattice model and including a local anisotropy term, we show, through Schrieffer–Wolff transformation, that local anisotropy is equivalent to an anisotropic Kondo interaction (J∥≠J⊥). The competition and coexistence between ferromagnetism and Kondo effect in this effective model is studied within a generalized mean-field approximation. Several regimes are obtained, depending on the parameters, exhibiting or not coexistence of magnetic order and Kondo effect. Particularly, we show that a re-entrant Kondo phase at low temperature can be obtained. We are also able to describe phases where the Kondo temperature is smaller than the Curie temperature (TK<TC). We propose that some aspects of uranium and neptunium compounds that present coexistence of Kondo effect and ferromagnetism can be understood within this model. •We apply the Schrieffer–Wolff transformation to the two orbital Anderson lattice.•Anisotropy breaks the symmetry between parallel and perpendicular Kondo interactions.•Two regimes are described: a re-entrant Kondo phase and a region with TK<TC.•Our results are in agreement with the experimental evidences of coexistent phases.