https://doi.org/10.1007/s100510050102
Dynamical mean-field theory of a simplified double-exchange model
Institute of Metal Physics, Ural Division of Russian Academy
of Sciences, Kovalevskaya str. 18, Yekaterinburg, 620219 Russia
Received:
28
May
1999
Revised:
14
July
1999
Published online: 15 March 2000
Simplified double-exchange model including transfer of the itinerant electrons
with spin parallel to the localized spin in the same site and the indirect
interaction J of kinetic type between localized spins is comprihensively
investigated. The model is exactly solved in infinite dimensions. The exact
equations describing the main ordered phases (ferromagnetic and
antiferromagnetic) are obtained for the Bethe lattice with (z is
the coordination number) in analytical form. The exact expression for the
generalized paramagnetic susceptibility of the localized-spin subsystem is also
obtained in analytical form. It is shown that temperature dependence of the
uniform and the staggered susceptibilities has deviation from Curie-Weiss
law. Dependence of Curie and Néel temperatures on itinerant-electron
concentration is discussed to study instability conditions of the
paramagnetic phase. Anomalous temperature behaviour of the chemical potential,
the thermopower and the specific heat is investigated near the Curie point.
It is found for J=0 that the system is unstable towards temperature phase
separation between ferromagnetic and paramagnetic states. A phase separation
connected with antiferromagnetic and the paramagnetic phases can occur only
at
. Zero-temperature phase diagram including the phase
separation between ferromagnetic and antiferromagnetic states is given.
PACS: 71.10.Fd – Lattice fermion models (Hubbard model, etc.)
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2000