Variational mean-field approach to the double-exchange model



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Alonso, J. L. and Fernández Pérez, Luis Antonio and Guinea, F. and Laliena, V. and Martín Mayor, Víctor (2011) Variational mean-field approach to the double-exchange model. Physical review B, 63 (5). ISSN 1098-0121

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It has been recently shown that the double exchange Hamiltonian, with weak antiferromagnetic interactions, has a richer variety of first- and second-order transitions than previously anticipated, and that such transitions are consistent with the magnetic properties of manganites. Here we present a thorough discussion of the variational mean-field approach that leads to these results. We also show that the effect of the Berry phase turns out to be crucial to produce first-order paramagnetic-ferromagnetic transitions near half filling with transition temperatures compatible with the experimental situation. The computation relies on two crucial facts: the use of a mean-field ansatz that retains the complexity of a system of electrons with off-diagonal disorder, not fully taken into account by the mean-field techniques, and the small but significant antiferromagnetic superexchange interaction between the localized spins.

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© 2001 The American Physical Society. We are thankful for helpful conversations to L. Brey, J. Fontcuberta, G. Gómez-Santos, C. Simon, J. M. de Teresa, and especially to R. Ibarra and V. S. Amaral. V.M.-M. was partially supported by MEC. We acknowledge financial support from Grant Nos. PB96-0875, AEN97-1680, AEN97- 1693, AEN97-1708, AEN99-0990 (MEC, Spain), and (07N/0045/98) (C. Madrid).

Uncontrolled Keywords:Spectral moments method; Diluted ising-model; Phase-separation; Colossal magnetoresistance; Ferromagnetic manganites; Manganese perovskites; Critical exponents; Electronic models; Doped manganies; Spin dynamics.
Subjects:Sciences > Physics
Sciences > Physics > Physics-Mathematical models
ID Code:40116
Deposited On:25 Nov 2016 08:16
Last Modified:25 Nov 2016 08:42

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