Investigating the mechanism of ferromagnetic exchange interaction in non-doped CeO2 with regard to defects and electronic structure

We report a systematic structural, electronic, and magnetic investigation on occurrence of ferromagnetism and its switch action in non-doped bulk ceria (CeO2). The magnetization measurements establish that the pristine CeO2 having a paramagnetic ground state can be driven to a ferromagnetic state at room temperature, when hydrogenated at 600 degrees C. The observed H-induced ferromagnetism is closely related to the oxygen vacancies and the Ce valence state. X-ray photoemission results depict that Ce ions reduce from 4+ to 3+ state along with creation of oxygen vacancies during the ferromagnetic transition. A parallel variation of carrier concentration, revealed by resistance measurements, seems to be a secondary effect of the oxygen vacancies creation. The F+ centers, i.e. the electrons in singly occupied oxygen vacancies, seem to play the key role in establishing the ferromagnetism in CeO2, in the framework of bound magnetic polaron model. The exchange mechanism shows a switch action such that one could remove the oxygen vacancies through re-heating the H-2-treated CeO2 and the ferromagnetism is subsequently vanished. (C) 2011 Elsevier B.V. All rights reserved.