Structural, morphological and electron spin resonance of Zn_0·7Ni_0.3Gd_xFe_2-xO₄ (0 ≤ x ≤ 0.1) nanoferrites synthesized via glycol-thermal method

The structural and magnetic properties of Zn_0·7Ni_0.3Gd_xFe_2-xO₄ (0 ≤ x ≤ 0.1) nanoferrites synthesized via the glycol-thermal method were systematically investigated. X-ray diffraction (XRD) confirmed the formation of a single-phase cubic spinel structure with crystallite sizes ranging from 8.6 nm to 18.7 nm, with no detectable secondary phases. Transmission electron microscopy (TEM) analysis revealed a morphology transition from spherical to cubic structures with increasing Gd content, influencing particle size distribution. Fourier-transform infrared (FTIR) spectroscopy corroborated the XRD findings, showing vibrational mode shifts due to lattice distortions, with Fe–O stretching bands consistently observed. Electron spin resonance (ESR) analysis demonstrated variations in the resonance magnetic field (Hᵣ), g-values, and peak-to-peak linewidth (ΔHpp), confirming bulk magnetization effects rather than isolated spin resonance, with spectral broadening primarily attributed to g-anisotropy, dipolar interactions, and exchange coupling. Magnetic characterization confirmed ferrimagnetic ordering, refuting prior claims of superparamagnetic behavior. Notably, the sample with x = 0.025 exhibited Young's modulus of 130 GPa and a resonance magnetic field of 2686 G, indicating its suitability for spintronic applications. These results underscore the critical role of Gd³⁺ in tuning the structural and magnetic properties of Zn–Ni ferrites, providing insight into their potential for next-generation spintronic and electronic applications.