Microstructural, magnetic, and dielectric properties of Er-substituted Ni-Cu-Zn ferrite nanoparticles

The structural, microstructural, magnetic, and dielectric properties of Ni_0.2Cu_0.4Zn_0.4Fe_2-xEr_xO₄ (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12) ferrites, synthesized via the sol-gel auto-combustion method, have been systematically investigated to explore their potential for high-frequency applications. X-ray diffraction analysis confirmed the formation of a single-phase cubic structure (space group Fd $\bar{3}$ m), with lattice parameter variations attributed to Er³⁺ substitution. The substitution induced localized distortions in the crystal lattice, affecting the grain size and porosity, as revealed by field-mission scanning electron microscopy. A nonmonotonic variation in porosity was observed, correlating with the dielectric properties of the material. The dielectric constant and loss tangent (tanδ) exhibited significant improvement at x = 0.06, indicating an optimal balance of electrical resistivity and reduced energy dissipation. These improvements are attributed to the enhanced electron exchange probability between Fe²⁺ and Fe³⁺, coupled with the suppression of eddy current losses due to Er³⁺ substitution. Magnetic measurements demonstrated that Er³⁺ substitution modifies the saturation magnetization and coercivity, further impacting the material's high-frequency performance. The interplay between microstructural parameters, such as grain size and porosity, and the dielectric properties was critical in determining the optimal composition for advanced technological applications. The composition x = 0.06 was identified as the most promising, providing a combination of structural stability, superior dielectric properties, and enhanced magnetic performance.