Local Structure Control of Manganese Oxide Nanoparticles Encapsulated by Amorphous SiO2

Spinel-structured manganese oxide (MMn2O4: M = Fe, Ni, Co, Zn) nanoparticles encapsulated in amorphous SiO2 were produced using our original wet chemical method. From the X-ray diffraction patterns, the diameters were estimated to range from 4 nm to 23 nm, depending on the annealing temperature. Bulk manganese oxide crystals are known to have the spinel structure, and a tetragonal structure with Jahn-Teller distortion is a stable and normal phase. This Jahn-Teller distortion is induced by Mn3+ ions at the octahedral B sites. However, we have successfully produced cubic structures consisting of FeMn2O4, CoMn2O4, and NiMn2O4 nanoparticles in which the local distortion is suppressed. In order to clarify the local structure, X-ray absorption fine structure (XAFS) and magnetization measurements were performed. The cubic and tetragonal structures were selectively obtained, and their magnetic properties were investigated. [DOI: 10.1380/ejssnt.2014.307]