Change in magnetic properties induced by swift heavy ion irradiation in CeO2

We have studied the magnetic properties of pure CeO2 irradiated with swift heavy ions. Experimental results showed that the ferromagnetism was induced even at room temperature by 200 MeV Xe ion irradiation. The value of saturation magnetization, Ms, systematically changes as a function of ion-fluence. The value of Ms increases with increasing the ion-fluence and reaches a maximum value at about the fluence of 2.0 × 1013/cm2, and then decreases. The X-ray diffraction (XRD) spectra show that the lattice constant of CeO2 increases with increasing ion-fluence. This result and our previous XPS result show that the ion-irradiation produced oxygen vacancies. The present study implies that the ferromagnetic behavior of the ion-irradiated CeO2 is attributed to the magnetic moments of localized 4f electrons on Ce3+ atoms, which are related to oxygen vacancies.