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Room temperature ferromagnetism in pure and Co- and Fe-doped CeO2 dilute magnetic oxide: effect of oxygen vacancies and cation valence

The evolution of reversible room temperature ferromagnetism (RTFM) has been investigated in Co- and Fe-doped (5% each) and non-doped CeO2 polycrystalline samples. Specimens with different oxygen vacancy (VO) concentration including the (i) as-synthesized, (ii) hydrogenated and (iii) re-annealed in air were investigated using SQUID magnetometry, x-ray diffraction and x-ray photoelectron spectroscopy. The influence of the electronic properties on the RTFM was examined/analysed systematically. Our findings confirm that the ferromagnetism observed in CeO2 originates due to the oxygen vacancies, supporting the VO mediated ferromagnetic exchange mechanism. Additionally, the cationic (cerium and transition metal) valence states play a crucial role.