Mn_xZn_1-xFe₂O₄ (x = 0.5, 0.6, 0.7) ferrite nanoparticles were synthesized by a thermal decomposition method. The synthesized particles were identified as pure spinel ferrite structures by x-ray diffraction analysis and they were calculated to be 15-20 nm in diameter by the Scherrer equation, depending on the composition. Ferrite nanoparticles are spherical in shape with a slight agglomeration in the FE-SEM image, and the particle size is about 20 nm, which was consistent with the value obtained by the Scherrer equation. The lattice parameters of ferrite nanoparticles monotonously decreased from 8.358 Å to 8.389 Å as the manganese concentration increased from 0.5 to 0.7. As the manganese content increases from x = 0.5 to 0.7, the saturation magnetization value increases from 76 emu/g to 63 emu/g. Mn_xZn_1-xFe₂O₄ toroidal samples were prepared by sintering ferrite nanoparticles at 1,250 ^oC and exhibited faceted grain morphology in FE-SEM images with a grain size of about 3 um regardless of manganese content. The cutoff frequency of the ferrite toroidal sample was estimated to be about 3MHz from the broad maximum point in the plot of imaginary magnetic permeability (μ”) vs. frequencies, which seems to be associated with domain wall resonance.

Keywords: Nanoparticles, MnZn ferrite, Superparamagnetic