NMR Determination of Metal Ion Distribution in Manganese Ferrite Prepared from Aqueous Solution

抄録

In order to determine the metal ion distribution in a new type manganese ferrite (MnFe₂O₄), which was prepared by precipitation from aqueous solution, the nuclear magnetic resonance (NMR) of Mn⁵⁵ was studied. In this ferrite, two separate resonance signals were observed, which were identified as associated with Mn²⁺ ions located at the tetrahedral (A-) and the octahedral (B-) sites respectively. By integrating those NMR spectra, it was decided that about 10% of Mn²⁺ ions are present at B-sites. Using the ratio of the amount of the Mn²⁺ ions located at A-sites to that at B-sites and the value of saturation moment (4.2μ_B), the metal ion distribution in this manganese ferrite was determined to be Mn_0.48²⁺Fe_0.52³⁺(Mn_0.06²⁺Mn_0.46³⁺Fe_1.02³⁺Fe_0.46²⁺)O₄. From the temperature dependence of the resonance frequency, the Curie temperature was estimated to be 770°K. The high Curie temperature compared with that of ordinary manganese ferrite (573°K) is explainable by the above metal ion distribution. It was found that the metal ion diffusion between A- and B-sites occurs at about 250°C, and above 450°C the metal ion distribution accords with that of ordinary manganese ferrite.