Comparative Structural Evolution and Size-dependent Magnetism of R2O3 (R = Yb, Er, Dy) From the Nano-to-bulk-like Regime

Abstract We report a systematic study of the structural and magnetic properties of rare-earth sesquioxides Yb 2 O 3 , Er 2 O 3 , and Dy 2 O 3 across a broad range of particle sizes obtained via co-precipitation and subsequent thermal annealing (500–900 °C). X-ray diffraction analysis reveals progressive grain growth with increasing temperature, with Dy 2 O 3 exhibiting notably faster coarsening than Yb 2 O 3 and Er 2 O 3 . Temperature-dependent susceptibility measurements indicate Curie-type paramagnetism for all compounds, while low-temperature anomalies suggest contributions from finite-size effects, crystal-field splitting, or residual defects. Field-dependent magnetization at 5 K demonstrates a clear size dependence for Yb 2 O 3 and Er 2 O 3 , where the apparent saturation increases with particle size due to the reduction of surface disorder and the recovery of the full rare-earth moment. In contrast, Dy 2 O 3 shows nearly size-independent magnetization, which can be associated with its larger intrinsic moment and strong single-ion anisotropy, and rapid attainment of bulk-like grain sizes. These results highlight the interplay between particle size, surface effects, and crystal-field stabilization in determining the magnetic response of rare-earth oxides and provide guidelines for tailoring nanoscale magnetism in functional materials.