Self-propagating high temperature synthesis, structural morphology and magnetic interactions in rare earth Ho3+ doped CoFe2O4 nanoparticles

• Rare earth Ho3+ substituted CoFe2O4.
• XRD and IR spectra reveal the spinel structure.
• Magnetization and coercivity increased with Ho3+ substitution.

Substitution effect of rare earth trivalent Ho3+ ions on the composition, HoxCoFe2−xO4, with x varying from 0.0 to 0.1 in steps of 0.025 using sol–gel auto combustion route has been investigated. Examination of X-ray diffraction (XRD) patterns shows that all the samples consisted of ferrite phases of typical spinel cubic structure, and when Ho3+ ion content was x ⩾ 0.075, orthoferrite–HoFeO3 phase was detected. The micro and nanostructure of the synthesized Ho doped CoFe2O4 ferrites were investigated by scanning and transmission electron microscopy respectively. With increasing doping content of Ho3+ ions, the lattice constant, particle size and bulk density increased, and after an increase to its maximum value, the sample particle size and density dropped down. Cation distribution estimated from XRD patter revealed that the Co2+ and Ho3+ ions prefer to occupy octahedral B-site whereas Fe3+ ions are distributed over tetra- and octa-hedral site. Oxygen positional parameter shows larger values than its ideal value. The analysis of magnetic properties revealed that the saturation magnetization and coercivity of CoFe2O4 increased with the rare earth Ho3+ substitution.

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