Room temperature ferromagnetism in ceria nanorods and nanosheets: Influence of morphology and defects

Abstract

This study investigates the structural, chemical, and magnetic properties of cerium oxide (CeO₂) nanoparticles (NPs) with distinct morphologies, including nanorods (CeO₂ NR), nanosheets (CeO₂ NS), and polyhedral structures (CeO₂ poly). X-Ray Diffraction (XRD) analysis revealed significant variations in lattice microstrain and dislocation density, with CeO₂ NR exhibiting the highest values, followed by CeO₂ NS and CeO₂ poly. Transmission Electron Microscopy (TEM) micrographs confirmed the well-defined morphologies of the NPs, with CeO₂ NR showing an average width of 6 nm and length of 39 nm, while CeO₂ NS and CeO₂ poly presented average diameters of 14 nm and 27 nm, respectively. X-Ray Photoelectron Spectroscopy (XPS) analysis indicated that CeO₂ NR had the highest concentration of Ce³⁺ ions and oxygen vacancies, which correlated with its enhanced magnetic susceptibility and polaron magnetization. In contrast, CeO₂ poly exhibited a more stable structure with lower defect density, resulting in weaker magnetic properties. CeO₂ NS presented intermediate characteristics, structural distortion and magnetic behavior. The formation of small polarons and bound magnetic polarons (BMPs) in CeO₂ NR, resulted by high tensile strain and oxygen vacancy concentration, was identified as a key factor in promoting room-temperature ferromagnetic (RTFM) ordering. These findings highlight the critical role of morphology in tailoring the properties of CeO₂ nanoparticles, offering valuable insights for the design of advanced functional materials for applications in spintronics, catalysis, and energy storage.