Structural, magnetic, and dielectric tailoring of Nd3+-substituted Ni0.7Zn0.3Cr0.5Fe1.5-xNdxO4 nanoferrites

Abstract

Nd³⁺-substituted Ni_0.7Zn_0.3Cr_0.5Fe_1.5-xNd_xO₄ nanoferrites (0.00 ≤ x ≤ 0.05) were synthesized by the sol–gel auto-combustion route to examine how rare-earth substitution tunes the structural, dielectric, electrical, and magnetic characteristics of Ni–Zn ferrites. X-ray diffraction with Rietveld refinement confirmed the formation of a single-phase cubic spinel structure for all compositions. The larger ionic radius of Nd³⁺ compared with Fe³⁺ causes lattice expansion/local strain and indicates preferential incorporation into the octahedral B-site network, as also supported by the Bertaut-type cation-distribution analysis. TEM revealed a progressive reduction in particle size with increasing Nd content, consistent with the observed microstructural evolution. Elemental mapping/EDS supported a uniform spatial distribution of constituent elements across the investigated samples. FTIR spectra showed ferrite-related low-wavenumber metal–oxygen vibrational features, with band-shape modifications attributable to Nd-induced perturbation of the local bonding environment. Dielectric spectroscopy showed the expected dispersion of ε′ and tanδ with frequency; moreover, ε′ and dielectric loss decrease with Nd substitution, suggesting suppression of space-charge/interfacial polarization and reduced charge carrier mobility at grain boundaries. The frequency dependence of σ_ac follows the typical ferrite response and is consistent with a hopping-assisted conduction mechanism; σ_ac decreases with increasing Nd content, indicating inhibited hopping between localized states (e.g., Fe²⁺/Fe³⁺). Room-temperature M–H measurements confirmed soft ferrimagnetic behavior for all compositions, while the gradual reduction in saturation magnetization and coercivity with Nd incorporation is correlated with weakened A–B superexchange interactions, magnetic dilution, increased Yafet–Kittel spin canting, and modified anisotropy. Overall, Nd³⁺ substitution provides a viable pathway to tailor the microstructure and multifunctional response of Ni–Zn–Cr ferrites for high-frequency and low-loss magnetic/dielectric device applications.