Intrinsic ferromagnetism in CeO2: dispelling the myth of vacancy site localization mediated superexchange

Abstract

Intrinsic ferromagnetism in CeO2 is a source of controversy in the literature and has been linked to the excess electronsleft over upon oxygen vacancy formation on Ce sites neighbouring the vacancy.A recent theoretical study (Han et al 2009 Phys. Rev. B 79 100403) concludedthat increased vacancy concentration changes the localization behaviour ofCeO2, resulting in some degree of charge localization in the vacancy site itself, which leads tosuperexchange and polarization effects that enhance the stability of ferromagnetism. Inthis report, we show conclusively that oxygen vacancy concentrations of up to12.5% do not cause localization in the vacancy site, and that this is not responsible for anyenhanced ferromagnetism. Investigation of oxygen vacancies on the (111), (110)and (100) low index surfaces also show no evidence for ferromagnetic preference.