%0 Journal Article
%A Alonso, J. L.
%A Fernández Pérez, Luis Antonio
%A Guinea, F.
%A Laliena, V.
%A Martín Mayor, Víctor
%T Variational mean-field approach to the double-exchange model
%D 2011
%@ 1098-0121
%U https://hdl.handle.net/20.500.14352/42572
%X 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.
%~