Effect of sintering temperature on the structural, morphological, electrical, and magnetic properties of Ni–Cu–Zn and Ni–Cu–Zn–Sc ferrites.

Polycrystalline Ni_0.3Cu_0.2Zn_0.5Fe₂O₄ and Ni_0.3Cu_0.2Zn_0.5Sc_0.05Fe_1.95O₄ compounds have been prepared by standard solid-state reaction technique and sintered at 1000, 1100, 1150, 1200, and 1250 °C for 5 h in air. The effect of sintering temperature on the structural, morphological, magnetic, dielectric, and electrical properties of these spinel ferrites has been studied thoroughly and comparatively. Formation of the single-phase cubic spinel structure of these compositions is confirmed by X-ray diffraction analysis. The lattice constant increases with sintering temperature as well as with 5% scandium (Sc³⁺) doping in Ni–Cu–Zn ferrite. Surface morphology reveals that the grain size increases with sintering temperature. Among the prepared ferrites, Ni_0.3Cu_0.2Zn_0.5Sc_0.05Fe_1.95O₄ has the maximum density (5.05 × 10³ kg/m³) at sintering temperature 1150 °C, which gives the highest value of initial permeability. It is observed that initial permeability varies with sintering temperature, and it gives the maximum value at optimum sintering temperature. It is noted that Curie temperature decreases with 5% Sc³⁺ ions doping, whereas it slightly increases with increasing sintering temperature for both compositions. Ni_0.3Cu_0.2Zn_0.5Fe₂O₄ compound shows the highest Curie temperature 418 °C. Dielectric constant, dielectric loss factor and AC electrical conductivity decrease with 5% Sc³⁺ ions doping in Ni–Cu–Zn ferrite. The initial permeability decreases sharply at Curie temperature, which indicates a high degree of compositional homogeneity. The 'Hopkinson' peak is observed just below the Curie temperature in the real part of initial permeability versus temperature graphs. The mechanism of dielectric polarization and electrical conductivity has been explained based on the electron hopping between Fe³⁺ and Fe²⁺ ions. The variation trend of complex impedance and AC electrical conductivity reveals the semiconducting behavior of the ferrite samples. Formation of partial semicircles in the Z^/-axis indicates that relaxation process is non-Debye type. The investigated ferrites show relatively high initial permeability, low magnetic loss, and low electrical conductivity in a wide frequency range, which make them potential candidate for various practical applications such as small and compact power suppliers for computers, microprocessors, microwave electronic devices, etc. [ABSTRACT FROM AUTHOR]