Vacancy‐Controlled Lattice Dynamics and Magnetism in Mn‐Doped CeO 2−δ Nanocrystals

Mn‐doped nanocrystals provide a model system to quantify how defect chemistry controls emergent magnetism in a wide‐gap oxide. Single‐phase fluorite () nanocrystals exhibit nonmonotonic changes in lattice parameter, microstrain, and crystallite size that signal competing elastic responses to Mn doping and oxygen vacancies. A joint analysis of Mn K‐edge and Ce L 3 ‐edge XANES with a constrained phonon‐confinement treatment of the Raman mode yields the oxygen nonstoichiometry and its partition among –, –, and – complexes. The evolution of Raman linewidths, defect bands near 600 , and asymmetric low‐frequency tails maps a crossover from dispersed vacancy dipoles to correlated Mn– aggregates. Zero‐field‐cooled and field‐cooled magnetization curves at 0.1 T are captured by a blocked superparamagnetic ensemble of Mn– entities, while the high‐temperature inverse susceptibility is consistent with a Mn spin sublattice with predominant antiferromagnetic exchange and a Dzyaloshinskii–Moriya canting contribution induced by local inversion breaking at oxygen‐defective Mn–O–Mn bridges. Isothermal loops reveal a temperature‐driven fragmentation of this defect‐mediated magnetic polaron network into many small, weakly correlated entities.