Spectral density approach to the double exchange model

In rare-earth manganites the itinerant eg-electrons interact via exchange coupling with localized t2g-electrons which constitute the spin background. This fact is taken into account in the double exchange model DEM. The limit realistic to manganites is the strong coupling limit where the Hundʹs rule coupling constant between eg- and t2g-electrons is large compared to the eg-hopping integral. The spectral density approach, a reliable scheme in the strong coupling limit, has been adopted to obtain the density of states DOS for the eg-band. In this limit, the eg-band splits into two bands with different weights for spin-up and spin-down states. In the ferromagnetic state, the effective band width of the split band depends on the spin state of the eg-electron. Within the framework of the model and the approximation, it is observed that the temperature drives the half-metal to metal transition.