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

Abstract

In order to determine the metal ion distribution in a new type manganese ferrite (MnFe 2 O 4 ), which was prepared by precipitation from aqueous solution, the nuclear magnetic resonance (NMR) of Mn 55 was studied. In this ferrite, two separate resonance signals were observed, which were identified as associated with Mn 2+ ions located at the tetrahedral ( A -) and the octahedral ( B -) sites respectively. By integrating those NMR spectra, it was decided that about 10% of Mn 2+ ions are present at B -sites. Using the ratio of the amount of the Mn 2+ 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 0.48 2+ Fe 0.52 2+ (Mn 0.06 2+ Mn 0.46 3+ Fe 1.02 3+ Fe 0.46 2+ )O 4 . 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.