Zn-Co co-doped spinel ferrite and strontium hexaferrite nanocomposites obtained by “one-pot” green sol-gel synthesis: A study of the ferroelectric, magnetic and electrical properties

The one-pot green sol-gel synthesis procedure using mandarin peel extract as the reducing agent and nitrate metal precursors with calcination at 950 °C was applied to obtain Zn-Co spinel ferrite (magnetically soft) and strontium hexaferrite (magnetically hard) nanocomposites with spinel ferrite/hexaferrite content ratios of 50:50 (SH55), 60:40 (SH64) and 70:30 (SH73). Analysis of the measured X-ray diffraction patterns showed magnetoplumbite (M-type) strontium hexaferrite with zinc and cobalt incorporated into this phase forming SrCo0.2Zn0.2Fe11.6O18.8 with a c/a lattice ratio of ∼3.92 and cubic spinel zinc-cobalt ferrite phase with lattice parameter a ∼8.42 Å. The crystallite size of the hexaferrite phase decreased as the content of spinel ferrite phase increased. Specifically, the hexaferrite phase platelets were 46 nm wide and 27 nm thick for SH55, and 36 nm wide and 22 nm thick for SH73. Meanwhile, the spinel ferrite phase had a consistent crystallite size of 24–25 nm. X-ray photoelectron spectroscopy confirmed successful incorporation of Fe, Sr, Zn, Co, and O into the produced nanocomposites. Room-temperature ferromagnetic hysteresis loops showed a spring coupling behavior with coercivity decreasing from 115.8 (SH55) to 41.9 Oe (SH73) and saturation magnetization increasing from 18.2 (SH55) to 38.2 emu/g (SH73) with the increase in the spinel phase content. Room-temperature ferroelectric loops recorded at a frequency of 100 Hz and showed maximal polarization of 147.6–161.3 nC/cm2 and remanent polarization from 40.2 to 35.8 nC/cm2. The Arrhenius dependence of the DC conductivity on temperature was in line with the Mott model for phonon-assisted hopping of small polarons. The conductivity changed with frequency in accordance with the Jonscher's power law. The correlated barrier model described the conduction mechanism, while the Kohlrausch, Williams and Watts function explained the transition from long-range to short-range hopping and non-Debye relaxation mechanism for the analyzed spinel ferrite/hexaferrite nanocomposites. © 2025 Elsevier Ltd and Techna Group S.r.l.