We consider the possible formation of spin polarons in the double exchange model at finite temperatures. We show that the average size of a spin polaron in this model increases as the temperature decreases. Based on this, we argue that the transition to the ferromagnetic phase in the double-exchange model happens when the spin polarons start overlapping. The effect of the external field is shown to reduce the effective temperature and thus to increase the size of the polarons. The theory predicts a linear increase of Tc versus the applied external magnetic field, a temperature dependence of the magnetic susceptibility above Tc that deviates from Curie-Weiss behavior, and an increase of Tc as the electron/hole density increases.
- Double exchange
- Spin polaron
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics