Comportamento dos fônons e magnetismo gerado por vacâncias em nanocristais de CeO2− dopado com Mn

Abstract

We investigated the influence of doping CeO2 nanocrystals with Mn through structural, spectroscopic, and magnetic analyses. The materials were synthesized by the sol-gel method and characterized by X-ray diffraction, X-ray absorption spectroscopy (XANES), Raman spectroscopy, and magnetic measurements. The results of Rietveld refinement together with the Raman spectrum confirm the formation of a single phase of CeO2 with a fluorite-type cubic structure. These results show that Mn insertion modifies the lattice parameters, crystallite size, and microdeformation in a non-monotonic manner, revealing a balance between local disorder and lattice relaxation induced by phonons and vacancy formation. The XANES results reveal mixed valence of Mn ions as Mn3+ /Mn2+ , resulting in charge compensation through partial reduction of Ce4+ to Ce3+ . The ZFC/FC curves suggest an anisotropic distribution originating from Mn–vacancy and show blocked superparamagnetic behavior at low temperatures. The study identified an antiferromagnetic regime derived from Dzyaloshinskii-Moriya (DM) influenced by oxygen vacancies. These results present a framework that quantifies the defect chemistry and magnetic behavior in (Ce1−xMnxO2−, 0 ≤ x ≤ 0.09) nanocrystals, highlighting the role of oxygen vacancies and doping-induced structural disorder.