Surface-sensitive magnetism of mesoscopic hollow CeO2 spheres

• Published in: Materials science & engineering. B, Solid-state materials for advanced technology Vol. 274; p. 115481
• Main Authors: Hsu, Pei-Kai, Chen, Yi-Che, Gloter, Alexandre, Chen, Hong-Chieh, Nestor Tseng, Eric, Chen, Shih-Yun, Song, Jenn-Ming
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01.12.2021; Elsevier BV
• Subjects: Cerium oxides; Concentration gradient; Defect; Defect annealing; Ferromagnetism; Hollow spheres; Magnetic properties; Magnetic saturation; Magnetism; Microscopy; Oxides; Room temperature; Spectroscopy; Spheres; Surface roughness; Surface structure; Spectroscopy; Oxides; Defect; Hollow spheres; Magnetism; Microscopy
• ISSN: 0921-5107; 1873-4944
• DOI: 10.1016/j.mseb.2021.115481

[Display omitted] •The content and distribution of defect of micro-scale H-CeO2 spheres are controlled by the reaction of HNO3 and annealing.•Shell structure was investigated via detailed microscopy and spectrum analysis.•The width of the defective layer, degree of aggregation of Ce3+, and the distribution character has been tailored.•Having a uniform defect layer and continuous defect distribution is critical for the formation of high magnetization of the hollow sphere.•The presence of continuous defective surface layer provides additional contributions for magnetism. This study demonstrates magnetism of mesoscopic hollow ceria spheres (H─CeO2) with different defect distribution characteristics. The content and distribution of defect of micro-scale hollow spheres are controlled by varying the reaction with HNO3 and the annealing process. The obtained spheres are divided into three groups according to the surface structure, defect content and defect distribution of the shell. Group I is characterized by rough sphere surface and with large ceria clusters. Group II has relatively continuous surface defective layers and reduced surface roughness of the sphere. Group III has a continuous and smooth surface defective layer, and a decreasing gradient of Ce3+ concentration inside this layer. All spheres were ferromagnetic at room temperature. Saturation magnetization from high to low is in the sequence: group III, group II, and group I. The strongest magnetism is obtained for the samples subjected to the reaction with 1 M HNO3 for 60 min and then annealed, in which defects are distributed homogeneously within the surface thin layer and the sphere surface is smooth. We thus conclude that the surface plays the major role in the magnetic behavior of micro-scale hollow sphere.