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Ribeiro L.C.,Centro Federal Of Educacao Tecnologica Celso Suckow Da Fonseca Cefet Rj Uned Ni | Ribeiro L.C.,University of Alicante | Hamad I.J.,Pontifical Catholic University of Rio de Janeiro | Hamad I.J.,National University of Rosario | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

We analyze the transport properties of a double quantum dot device with both dots coupled to perfect conducting leads and to a finite chain of N noninteracting sites connecting both of them. The interdot chain strongly influences the transport across the system and the local density of states of the dots. We study the case of a small number of sites, so that Kondo box effects are present, varying the coupling between the dots and the chain. For odd N and small coupling between the interdot chain and the dots, a state with two coexisting Kondo regimes develops: the bulk Kondo due to the quantum dots connected to leads and the one produced by the screening of the quantum dot spins by the spin in the finite chain at the Fermi level. As the coupling to the interdot chain increases, there is a crossover to a molecular Kondo effect, due to the screening of the molecule (formed by the finite chain and the quantum dots) spin by the leads. For even N the two Kondo temperatures regime does not develop and the physics is dominated by the usual competition between Kondo and antiferromagnetism between the quantum dots. We finally study how the transport properties are affected as N is increased. For the study we used exact multiconfigurational Lanczos calculations and finite-U slave-boson mean-field theory at T=0. The results obtained with both methods describe qualitatively and also quantitatively the same physics. © 2014 American Physical Society. Source

Vargas E.,University of Chile | Vargas E.,University of Santiago de Chile | Melo W.W.M.,Centro Federal Of Educacao Tecnologica Celso Suckow Da Fonseca Cefet Rj Uned Ni | Allende S.,University of Santiago de Chile | And 5 more authors.
Materials Chemistry and Physics | Year: 2015

Using a simple method we produce polyethylene film with embedded chains of cobalt nanoparticles. The crystalline magnetic nanoparticles were synthesized through a simple chemical reduction method at room temperature using ultrasonic assistance. These particles were incorporated in a polyethylene matrix using a solution blending mechanism under an external magnetic field. The morphology and magnetic properties of Co nanoparticle aggregates were studied experimentally and by means of Monte Carlo simulations, showing a chain-like structures due to the strong dipolar interaction between aggregates. The hysteresis loops reveal typical ferromagnetic behavior at room temperature and magnetic anisotropy associated to a linear ordering of particles into the polymeric matrix. Numerical results confirmed the chain-like character of the aggregates and that an external magnetic field aligns them along its direction. The low-cost of the fabrication process of these polymeric magnetic films give them a strong potential for industrial and technological applications. © 2015 Elsevier B.V. Source

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