Seminários

Seminários de Mecânica Estatística

O seminário de Mecânica Estatística desta semana (6a feira, 24/05/2013) será apresentado às 16:00h na sala A5-01 do Instituto de Física.

Título: Models for Complex Magnetic Systems

Apresentador: Sergio G. Magalhães (Instituto de Física da UFF)

Resumo:
We discuss the theoretical approaches used to describe the competition among
Kondo effect, spin glass (SG) phase, ferromagnetic (FE) and antiferromagnetic
(AF) order in disordered cerium systems such as CeNi_(1−x)Cu_x and
Ce_2Au_(1−x)Co_xSi_3 . In these approaches, the model used was the Kondo
lattice model with a random exchange interaction Jij between localized f-spins
called here Kondo-Ising model. Firstly, several types of randomness for Jij
were tested as the Sherrington-Kirpatrick, the Hopfield and van Hemmen model for
spin glasses to explain the magnetic part of the experimental phase diagram of
CeNi_(1−x)Cu_x and Ce_2Au_(1−x)Co_xSi_3 [1,2,3]. It should be remarked that for
the van Hemmen type of ramdomness, the disorder can be treated without the use
of the replica method. Then, the Kondo-Ising model was reformulated replacing
f-spins by clusters of f-spins [4]. Finally, a random field was added to the
Kondo-Ising model in order to describe some aspects of the experimental phase
diagram of the CeNi_(1−x)Cu_x [5].
[1] A. Theumann, B. Coqblin, S. G. Magalhaes, A. A. Schmidt, Phys. Rev. B 63
(2001) 054409.
[2] S. G. Magalhaes, F. M. Zimmer, P. R. Krebs, B. Coqblin, Phys. Rev. B 74
(2006) 014427.
[3] S. G. Magalhaes, F. M. Zimmer, B. Coqblin, Phys. Rev. B 81 (2010) 094424..
[4] F. M. Zimmer, S. G. Magalhaes, B.Coqblin, Physica B 404/19 (2009) 2972.
[5] S. G. Magalhaes, F. M. Zimmer, B. Coqblin, J. Magn. Magn. Mat. 339 (2013)
30.