Surface and interface mediated magnetism in mesoscopic ceria@carbon core–shell structures

Abstract

CeO2@C submicron core–shell structure was prepared by a two-step synthesis method, and the ceria shell thickness and its microstructure were precisely controlled by the precursor composition and annealing process. The results show that forming the thin ceria shell by aggregating nanoparticles on the surface of the carbon sphere is more favorable for forming ferromagnetism than merely dispersed ceria nanoparticles. The saturation magnetization increases with decreasing shell thickness, indicating the contributions of surfaces and interfaces to the magnetism. Furthermore, high-temperature reduction results in shell densification and the aggregation of defects at the surface. The spectroscopic and microscopic measurements reveal that in such cases, a continuous defect-rich area with a sub-nanometric thickness, doped with electrons extends over the whole surface of the mesostructure. The magnetic strength difference caused by adjusting the thickness of this defective layer from several nanometers to sub-nanometric width can reach 360 times, suggesting that the magnetization of these mesoscopic systems is related to the presence of these quasi-2D electron-rich regions on the surface. This study shows the applicability of giant orbital magnetism to mesoscopic systems, and the results can also provide a reference for the subsequent synthesis of magnetic materials.