Electronic and magnetic properties of Gd-doped EuO

Abstract

To study electron states and magnetism in Gd-doped EuO theoretically, we first calculate the spin-polarized density of states (DOS) by applying the dynamical coherent potential approximation (dynamical CPA) for two simple models: the $s$-$f$ model of electron-doped EuO and a model of Eu${}_{1\ensuremath{-}x}$Gd${}_{x}$O. On the basis of the spin-polarized DOS, we calculate the total energy of electrons interacting with $f$ spins through an exchange interaction. Then, we obtain the magnetization as a function of the temperature $T$, by minimizing the free energy. We discuss the mechanism of the electron-induced increase in the Curie temperature ${T}_{C}$, the origin of the anomalous magnetization curve, and the existence of a threshold Gd concentration for increasing ${T}_{C}$. We investigate the effect of on-site attractive potential that yields an impurity level when the Gd concentration is low. We also discuss the relationship between the redshift of the optical absorption edge and the increase in the ${T}_{C}$ of Gd-doped EuO.