Cation distribution and Mössbauer spectral studies of Mg0.2Mn0.5Ni0.3InxFe2−xO4 ferrites (x = 0.0, 0.05 and 0.10)

The effect of substitution of diamagnetic indium ions in Mg–Mn–Ni ferrite with the composition Mg0.2Mn0.5Ni0.3InxFe2−xO4 (x = 0.0, 0.05 and 0.10) synthesized by citrate precursor technique has been investigated. Crystallographic and magnetic properties have been investigated using X-ray diffraction, TEM, VSM and Mössbauer spectroscopy. The single phase cubic spinel structure of these samples has been confirmed from X-ray diffraction analyses. In3+ ions initially prefer tetrahedral A-site up to x = 0.05 due to which saturation magnetization and magnetic moment increases, followed by subsequent decrease when indium ions begin to occupy octahedral B-site for higher concentration of x. Magnetization measurements exhibit Neel’s collinear ferrimagnetic structure for samples up to x = 0.05. Mössbauer spectra of these samples studied at 300 K show two characteristic ferrimagnetic Zeeman sextets for x = 0.0, followed by relaxation phenomenon corresponding to x = 0.05 and 0.10. Mössbauer measurements also show dependence of Zeeman spectral lines on smaller particle size which is indicative of their superparamagnetic nature. The dependence of Mössbauer parameters such as isomer shift, quadrupole splitting, linewidth and hyperfine magnetic field on In3+ ions concentration have been discussed. The variation of hyperfine magnetic field with increasing In3+ ions content has been explained by Neel’s molecular field theory.

► Single phase Mg0.2Mn0.5Ni0.3InxFe2−xO4 ferrites were synthesized by citrate precursor method.
► Particle size decrease as diamagnetic indium content increases.
► The presence of doublets in the Mössbauer spectra of samples can be attributed to superparamagnetic relaxation due to extremely small size of crystallites.
► Mössbauer spectral studies show collapse of magnetic ordering due to smaller particle size.
► When indium ions go to A-site, it induces the structural perturbation on the B-site and there is site percolation of In3+ ions to octahedral B-site even when x < 0.10.