Valence state dependent room-temperature ferromagnetism in Fe-doped ceria nanocrystals

摘要

Room-temperature ferromagnetism was observed in undoped and Fe~(2+(3+))-doped CeO_2 nanocrystals. In Fe-doped samples the enhancement of ferromagnetic ordering occurs by changing the valence state of Fe ions, whereas Raman spectra demonstrated strong electron-molecular vibrational coupling and increase in oxygen vacancy concentration. Air annealing showed degradation of ferromagnetic ordering and appearance of hematite phase in Fe~(3+)-doped sample. The observed ferromagnetic coupling in Fe-doped samples, associated with the presence of magnetic ions mediated by single charged O~(2-) vacancies, demonstrated that valence state of dopant has a strong influence on magnetic properties of CeO_2 nanoparticles.