Magnetic Properties and X-ray Absorption Fine-Structure Spectra of CoMn2O4 Nanoparticles

CoMn2O4 (cobalt manganite) nanoparticles encapsulated in amorphous SiO2 cages were prepared by a wet chemical method. Two different structures of CoMn2O4 nanoparticles, cubic and tetragonal, were observed in the X-ray diffraction patterns. CoMn2O4 crystals usually form a tetragonal structure with Jahn-Teller distortion, and the cubic structure is unstable. X-ray absorption fine structure (XAFS) measurements were performed on the obtained samples. From the X-ray absorption near-edge structure spectra of the Mn K-edge, it was concluded that Mn ions had a valence of 3+. This ion distribution of cobalt manganites should easily induce Jahn-Teller distortion. The magnetization of each particle was measured using a superconducting quantum interference device magnetometer, and obvious differences between cubic and distorted tetragonal structures were observed in the magnetization curve.