Extrinsic Ferromagnetism In Epitaxial Co-Doped Ceo2 Pulsed Laser Deposited Films

We report on the structural and magnetic properties of 5 at. % Co-doped CeO2 films grown on LaAlO3(001) substrates by pulsed laser deposition. A series of epitaxially grown samples made under different oxygen partial pressures ranging from 10(-4) to 10(-1) mbar showed a ferromagnetic signal at room temperature. This signal is independent on the oxygen partial pressure during deposition. X-ray photoelectron spectroscopy showed an increasing concentration of defects as the oxygen pressure during deposition decreases. Although x-ray diffraction and transmission electron microscopy observations could not prove the existence of spurious phases, the temperature dependent variation in the magnetization suggests the existence of small magnetic Co clusters with a large distribution of blocking temperatures. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3481026]