Synthesis and Analyses of Acicular Spinel Iron Oxide Particles with Core-Shell Structure Containing Manganese Ferrite and Magnetite

Abstract

  Acicular spinel iron oxide particles with a core-shell structure containing manganese ferrite (MnFe₂O₄) and magnetite (Fe₃O₄) were synthesized by uniformly crystallizing MnFe₂O₄ on the surface of the magnetite particles in an alkaline dispersion. Crystallizing 50 wt% of MnFe₂O₄ on Fe₃O₄ led to an increase in the apparent lattice constant from 0.839 nm to 0.841 nm. Transmission electron microscopy (TEM) observations of the particle shape and lattice images showed that MnFe₂O₄ was uniformly crystallized on the surface of the magnetite particles and their acicular shape was maintained. The coercive force and saturation magnetization were almost constant at 29.5 kA/m and 80-81 Am²/kg, respectively, when the crystallized MnFe₂O₄ content ranged from 0 to 30 wt%. When the MnFe₂O₄ content was increased to 50 wt%, the coercive force and saturation magnetization slightly decreased to approximately 28.0 kA/m and 74.1 Am²/kg, respectively, reflecting the lower magnetization of MnFe₂O₄ compared to that of Fe₃O₄.