Effects of electronic modification and structural distortion on ferromagnetism in sputtered CeO₂ films with isovalent Sn⁴⁺ doping

The effects of isovalent doping on electronic and magnetic properties in sputtered polycrystalline Ce_1−xSn_xO₂ films were investigated. All the samples have a fluorite structure with [100] preferred orientation. The Sn doping helps to boost the magnetism in CeO₂, but has no significant impact when the doping content exceeds 6% (x > 0.06). Experimental analysis indicates that the magnetism may be directly associated with the structure distortion as well as the concentration of Ce³⁺ and oxygen vacancies. Theoretical calculations based on the density-functional theory suggest that the redox process of CeO₂ can be influenced by the presence of dopant. The superexchange mechanism through Ce–O–Ce interaction and F+ centers lying deep in the gap can ease the mediation of ferromagnetic coupling in the system. Meanwhile, there is a competition mechanism in electronic modification, causing the spin-polarization to have a maximum stability at a critical doping concentration.