Nanocrystalline Mn2+-doped magnetite (Fe3O4) particles of the composition MnxFe3−yO4(x=0.0,0.1,0.2,0.3,0.4and0.5;y=2x3), prepared using chemical precipitation under reflux with the Mn2+ ions substituting for Fe3+ ions rather than Fe2+ ones, are characterized mainly with XRD and 57Fe Mössbauer spectroscopy. All samples were found to have spinel-related structures with average lattice parameters that increase linearly with the Mn2+ concentration, x. The particle size for the samples varied from ∼8 nm to 23 nm. The oxidation of Fe2+ to Fe3+ at surface layers of the Fe3O4 nanoparticles leading to the formation of maghemite (γ-Fe2O3) was found to considerably weaken with increasing Mn2+ concentration. The percentage of the nanoparticles that exhibit short range magnetic ordering due to cationic clustering and/or superparamagnetism increases from 17% to 32% with increasing x. The dependence of isomer shifts of the 57Fe nuclei at the tetrahedral and octahedral sites on dopant Mn2+ concentration is emphasized. The electric quadrupole shifts indicate that the MnxFe3−yO4 particles undergo Verwey transition. The effective hyperfine magnetic fields at both crystallographic sites decrease with increasing Mn2+ concentration reflecting a size effect as well as a weakening in the magnetic super-exchange interaction. The Mössbauer data indicate that for x ≤ 0.2, the dopant Mn2+ ions substitute solely for octahedral Fe3+ ions whereas for x > 0.2 they substitute for Fe3+ at both tetrahedral and octahedral sites.
- Mössbauer spectroscopy
- Nanocrystalline particles
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Nuclear and High Energy Physics
- Condensed Matter Physics
- Physical and Theoretical Chemistry