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

• Published in: Materials chemistry and physics Vol. 132; no. 2-3; pp. 534 - 539
• Main Authors: Singhal, R.K., Kumar, Sudhish, Samariya, Arvind, Dhawan, M., Sharma, S.C., Xing, Y.T.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15-02-2012
• Subjects: Electronic structure; Magnetic materials; Sintering; X-ray photo-emission spectroscopy (XPS); Electronic structure; Magnetic materials; X-ray photo-emission spectroscopy (XPS); Sintering
• ISSN: 0254-0584; 1879-3312
• DOI: 10.1016/j.matchemphys.2011.11.066

► Hydrogenation induces ferromagnetism in paramagnetic CeO2 matrix. ► “Switch” action of ferromagnetism between hydrogenation and re-heating in CeO2. ► Ferromagnetism shows close relation with oxygen vacancies in magnetic dielectrics. ► The F+ centers play key role in ferromagnetism in CeO2.
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°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 H2-treated CeO2 and the ferromagnetism is subsequently vanished.