Analysis of grain growth, densification and functional properties of manganese substituted NiCuZn nanocrystalline ferrites

Abstract

Ni0.50-xMnxCu0.15Zn0.35Fe2O4 (with x values ranging from 0.00 to 0.25 in steps of 0.05) were synthesized by the sol-gel auto combustion method. Pellet and toroid shaped samples prepared from each compositions are sintered at various sintering temperatures, Ts, e.g. at 900º, 1000º, 1100º, 1200º and 1300ºC in air for 5-hour. Surface morphology and functional properties were studied as a function of Mn2+ content. Phase formation and surface morphology were surveyed by the X-ray diffraction method (XRD) and field emission scanning electron microscopy (FESEM), respectively. The XRD analysis showed that all compositions exhibit single phase spinel structure without any significant impurity peak. The lattice constant, a_0, increases with increase in Mn content obeying the Vegard’s law. This is due to the fact that the ionic radius of Mn2+ (0.89Å) is greater than Ni2+ (0.77Å). The crystallite size, D, was estimated by the Debye Scherer’s formula where nanocrystalline particles were obtained in the range from 20 to 28 nm. The average grain diameter is determined by the linear intercept method in which average grain size increases with increasing Mn content that reveals that Mn2+ acts as a grain growth accelerator. With increasing Mn2+ substitution in Ni0.50-xMnxCu0.15Zn0.35Fe2O4 the bulk density increases as well as X-ray density decreases. For increasing sintering temperature bulk density increases for all samples which contribute to the lessening of the material’s porosity consequently enhances the magnetic induction of ferrite .The magnetic properties of prepared samples were investigated in terms of complex initial permeability and DC magnetization measurement. The initial permeability is observed to increase with increase in Mn content. The real part of initial permeability,μ_i^/, remains fairly constant in the frequency range up to some critical frequency which is called resonance frequency,f_r.It is also found that the higher μ_i^/ the lower f_r of the material. This indeed approves with Snoek’s limit. With increasing Mn content along with increasing sintering temperature in Ni0.50-xMnxCu0.15Zn0.35Fe2O4 relative quality factor, RQF, increases while magnetic loss tangent, tan⁡〖δ_m 〗, decreases. The complex dielectric constant was measured as a function of frequency for all compositions.The Curie temperature, TC, is measured from temperature dependent permeability. It is perceived that TC decreases with increasing Mn content which may be attributed to the increase in distance between the moments of A and B sites, which is ensured by the increase in the lattice parameter with increasing Mn content. From the M-H loop, it is obtained that with increasing Mn content saturation magnetization is increased. All the ferrite samples show the low coercive forces, Hc, characteristic of soft magnetic materials in which with increasing Mn content coercivity was found to be decreased.