Room temperature ferromagnetism in Fe-doped CeO2 thin films grown on LaAlO3 (001)

Ce1 − xFexO2 − δ/LaAlO3(001) thin films (x = 0.01 and 0.03) have been prepared by pulsed laser deposition method and thoroughly characterized using X-ray diffraction (XRD), dc magnetization, near edge X-ray absorption fine structure (NEXAFS), and X-ray magnetic circular dichroism (XMCD). XRD data reveal a single-phase cubic structure with a strong crystallographic orientation along the (200) plane. Room temperature ferromagnetism is confirmed through isothermal hysteresis as well as temperature dependent magnetization measurements, which clearly show the ferromagnetic Curie temperature occurring at least above 350 K. The Fe L3,2 edge NEXAFS spectra for both Fe-doped thin films exhibit mixed valent Fe2+/Fe3+ states, whereas Ce M5,4 edge shows the 4+ state of Ce, throughout the doping. With the increase in Fe doping, Fe2+ state increases and a simultaneous decrease in magnetization value is also observed. The XMCD signal of both samples reveals the ferromagnetic ordering of substituted Fe ions in the ceria matrix. Our results indicate that ferromagnetism is intrinsic to the ceria system and is not due to any secondary magnetic impurity.