Enhanced room-temperature ferromagnetism in composite CeO₂/CeF₃ nanoparticles

A considerable enhancement of the room-temperature ferromagnetism is observed in the composite CeO₂/CeF₃ nanoparticles. The saturation magnetization for the composite CeO₂/CeF₃ nanoparticles (the average particle size ∼100 nm) is more than a half order of magnitude higher compared to the initial CeO₂ nanoparticles (the average particle size ∼30 nm). The composite CeO₂/CeF₃ nanoparticles are synthesized by fluorination of initial CeO₂ nanoparticles. For this purpose, the initial ceria powder is annealed in the vacuum followed by an intake in the furnace of gaseous tetrafluoromethane (CF₄). X-ray diffraction (XRD) patterns show that resulting powder has both CeO₂ and CeF₃ structures with the ratio CeO₂/CeF₃ depending on the temperature and the duration of the annealing. It is supposed that the CeF₃ structure forms on the surface of the CeO₂ nanoparticles as a result of the chemical reactions on the surface of the CeO₂. A considerable increase of the saturation magnetization in the CeO₂/CeF₃ nanoparticles compared to the initial, vacuum, and air annealed CeO₂ nanoparticles is supposed due to the interface CeO₂/CeF₃ structure produced by the applied method of fluorination. The present study suggests that adjusting the interface in the composite nanoparticles containing ceria is a perspective way to enhance the room temperature ferromagnetism. (copyright 2018 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)