Bound magnetic polarons and the insulator-metal transition in EuO

A new model is presented for the insulator-metal transition in Eu-rich EuO: At low temperatures the electrons are only very weakly bound to oxygen vacancies and conduction is metallic; near and above Tc the electrons localize and form bound magnetic polarons by ordering the Eu2+ spins neighboring the vacancy, thereby gaining exchange energy. Magnetic-susceptibility data are presented which support this model. © 1972 The American Physical Society.