Nanomaterials in the 1-100 nm range have significantly different chemical, physical, electrical, magnetic, and optical properties compared to bulk materials [1–3]. These distinct behaviour enable the development of next-generation devices, thereby advancing specialized fields such as nanoelectronics, nanomagnetism, nanophotonics, and nanomechanics [4–6]. Ferrite nanomaterials display multifunctional features that allow applications in magnetic devices, gas sensing, dielectric components, catalysis, adsorption, and biomedicine [7–10]. Spinel ferrites are supremely magnetic materials due to their superior electrical and magnetic properties. The general formula for these compounds is MFe₂O₄, where M represents divalent ion such as Zn²⁺, Co²⁺, Fe²⁺, Mg²⁺, Cu²⁺, Cd²⁺, Ni²⁺, or a combination thereof. Their crystal structure contains two interstitial sites: tetrahedral (A) sites, which host 64 ions, and octahedral (B) sites, which hold 32 ions. Spinel ferrites can be classified as normal, inverted, or mixed based on presence of divalent cations and Fe³⁺. Mixed ferrites are particularly useful owing to their exceptional tunability and functional adaptability [11].

The size, structure, and characteristics of ferrite nanoparticles are heavily influenced by their creation method. Ball milling, hydrothermal, microemulsion, and sol-gel methods are all common ways to prepare materials. Mn-Zn ferrite is a key spinel material recognized for its soft-magnetic characteristics, which include low core loss, high resistivity, high permeability, and saturation magnetization. These characteristics make it appropriate for use in noise filters, transformers, recording heads, and biomedical devices. In recent decades, substantial research has concentrated on improving ferrites' magnetic and electrical properties by substituting various divalent and trivalent cations via alternative synthetic techniques. Zn-substituted spinel ferrites are gaining attention due to their strong affinity for tetrahedral (A) sites, which allows for good customization of structural and functional features [12–16]. Choodamani et al. developed Mn_1 − xZn_XFe₂O₄ ferrites synthesized via solution combustion produced a pure spinel phase with crystallite sizes ranging from 47 to 80 nm. The x = 0.50 ferrites had the lowest dielectric constant, loss tangent, and AC conductivity, and magnetic measurements revealed a strong dependence of saturation magnetization and coercivity on Zn content [17]. Murugesan et al. studied Mn_1 − xZn_XFe₂O₄ nanoferrites produced using a solvent-free combustion technique. XRD revealed a pure cubic spinel structure, with crystallite sizes rising from 8.5 to 19.6 nm as zinc concentration rose. Electrical transport properties investigations revealed reduced conductivity and prominent grain-boundary effects, implying that Zn-substituted Mn ferrites are promising for high-frequency electronics [18]. Mostafa et al. revealed that Mn_1 − xZn_XFe₂O4 (x = 0–0.4) nano-ferrites were synthesized via flash auto-combustion and confirmed to form a cubic spinel phase. Increasing Zn content enhanced crystallinity, grain growth, and particle size, while SEM showed irregular grains. The nano-ferrite exhibited soft magnetic behavior with low coercivity, and mechanical properties improved with Zn substitution, with x = 0.4 showing the highest hardness and creep resistance [19]. Anwar et al. studied a detailed investigation of magnetic and magnetocaloric properties of polycrystalline Mn_1 − xZn_XFe₂O₄ (0.0 ≤ x ≤ 0.7). Magnetization measurements reveal that increasing Zinc content leads to a gradual decrease in saturation magnetization [20]. Researchers have intensively studied nano-ferrites, as production methods have a significant impact on particle size and associated properties. This work used a simple and cost-effective sol-gel approach to synthesized Mn_1 − xZn_xFe₂O₄ nano-ferrites, which provided good compositional control and homogeneous precursor mixing. In the present study, we systematically examine their structural, morphological, spectroscopic, and Electrical transport properties, with results discussed in following sections.

XRD patterns of nano-ferrite Zn_0.2Mn_0.8Fe₂O₄ are shown in Fig. 1. The presence of peaks (111), (220), (311), (222), (400), (422), (511), (440), and (622) in the XRD patterns confirms the spinel cubic Fd3̅m space group as the main phase and secondary phase of α-Fe₂O₃. [21]. Diffraction peaks and their corresponding Bragg planes align well with the standard JCPDS card no. 00–152–8317, for cubic Fd3̅m space group and JCPDS card no. 00–210–8027 for secondary phase of α-Fe₂O₃. Secondary phase of α-Fe₂O₃ indicates that Fe has oxidized into this compound, consistent with the fact that α-Fe₂O₃ forms during synthesis [22]. The peaks marked with (*) reflect the breakdown of ferric nitrate into α-Fe₂O₃ before the formation of spinel ferrite [23–25].

Average crystallite size was predicted by Debye–Scherrer Eq. (1):

d = (1)

Where d is crystallite size, λ is X-ray wavelength (Cu Kα, 1.5406 Å), β is full width at half maximum (FWHM), and θ is Bragg angle. Crystallite sizes formulated by the Debye–Scherrer equation were approximately 32 nm for Zn_0.2Mn_0.8Fe₂O₄, indicating the nanoscale nature of the synthesized materials.

Figure 1. XRD patterns of nano-ferrite Zn_0.2Mn_0.8Fe₂O₄.

The body-centered cubic (BCC) structure of the secondary phase’s α-Fe₂O₃ makes it difficult for them to soften into ferrite phase with the face-centered cubic (FCC) structure [26]. X-ray diffractograms make it simple to identify traces of these matching secondary phases. According to findings in the literature, MnFe₂O₄ and substituted MnFe₂O₄ exhibit more favorable secondary phase development. For the compositions x = 0.34 and 0.5, Airimioaei et al. studied that 0.2% and 0.3% of ortho-ferrite Mn₂O₃ and 10.4% and 18.3% of antiferromagnetic α-Fe₂O₃ phase in Mn_xNi_1−xFe₂O₄ [27]. The emergence of α-Fe₂O₃ and Mn₂O₃ secondary phases is likely due to the oxidation of Mn²⁺ at the B-sites, as

Mn²⁺+Fe³⁺ → Mn³⁺+ Fe²⁺ (2)

By using neutron diffraction, Ghazanfaret et al. found that 30% of Mn³⁺ ions occupy the octahedral (B) sites in Zn_1 − xMn_xFe₂O₄, although Fe²⁺ is also present for charge compensation [28]. However, the literature that is now available provides a thorough explanation of secondary phase development and how it varies with heat treatment. The rate of oxidation and reduction is higher in MnFe₂O₄ than in other cubic ferrite systems. Heat treatment and the nearby oxygen atmosphere may have an impact on this. The ferrite phase oxidizes and decomposes in the following ways at low sintering temperatures because external oxygen environment prevails over intrinsic oxygen pressure within the nano-ferrite.

During the sintering process, several inert gas atmospheres have been employed to prevent oxidation [29, 30]. Conversely, thermal energy raises pressure of inner oxygen atmosphere at higher sintering temperatures. This pressure becomes sufficiently high above the surrounding oxygen to prevent the ferrite phase from decomposing into secondary phases.

FE-SEM was performed to examine surface morphology of synthesized nano-ferrite Zn_0.2Mn_0.8Fe₂O₄, as illustrated in Fig. 2 (a-d). The micrographs taken at various magnifications show a dense surface that is mostly made up of structures that resemble nanorods with a small amount of aggregation. The uniform distribution and interconnectedness of the rods suggest homogenous nucleation and regulated development throughout the sol-gel synthesis process. A partially porous architecture, which can promote electrolyte ion diffusion and enhance electrochemical accessibility, is suggested by the nanorod fine pores. As a result, the Zn_0.2Mn_0.8Fe₂O₄ nanorod morphology shows promise for multifunctional applications such as supercapacitors, magnetically responsive devices, photocatalytic pollutant degradation, and electromagnetic interference (EMI) shielding materials, where high surface activity and conductivity is critical for optimal performance.

HR-TEM images of the nano-ferrite Zn_0.2Mn_0.8Fe₂O₄ are shown in Fig. 3 (a-b). Micrographs of HR-TEM demonstrate the growth of well-defined nanorods and aggregated nanoparticles with average diameters ranging from 40 to 80 nm. The interplanar spacing corresponds to the (311) plane of the cubic spinel ferrite phase, which is reliable with XRD data. The consistent contrast and crisp lattice fringes confirm the high level of crystallinity attained after calcination. Selected area electron diffraction (SAED) patterns of nano-ferrite Zn_0.2Mn_0.8Fe₂O_4, shown in Fig. 3 (c), display multiple bright rings, confirming polycrystalline nature of the nanoparticles. The observed rings agree with (220), (311), (400), (511), and (440) crystallographic planes of spinel ferrite phase, consistent with Debye–Scherrer characteristic patterns. Figure 3 (d) EDS was attempting to ascertain the elemental makeup of nano-ferrite Zn_0.2Mn_0.8Fe₂O_4, which confirms occurrence of Zn, Mn, and Fe elements in nano-ferrite. The mixture of quasi-square and rod-like features revealed in HR-TEM agrees with the FE-SEM results. Zn Substitution nano-ferrite emphasizes the partial anisotropic growth along favored crystallographic orientations, which are suitable for electron transport, magnetic ordering, and electrochemical performance.

Figure 4 (a). Room temperature Raman spectra of the nano-ferrite Zn_0.2Mn_0.8Fe₂O₄. (b) PL emission spectra of the nano-ferrite Zn_0.2Mn_0.8Fe₂O₄.

Raman scattering of nano-ferrite Zn_0.2Mn_0.8Fe₂O₄ was investigated at room temperature using Raman spectroscopy. Spinel ferrite crystal structure MnFe₂O₄ has four Raman active modes: A_1g + E_g + 3T_2g [31].

Figure 4 (a) shows Raman spectra of nano-ferrite Zn_0.2Mn_0.8Fe₂O₄ at 200–700 cm^− 1. Figure 4 (a) reveals that Raman spectra of the material had 3 Raman modes, T_2g, E_g, and A_1g, at 220–240, 280–320, and 600–620 cm^− 1, correspondingly, which closely matched modes in earlier reported data [32].

The PL spectra of nano-ferrite Zn_0.2Mn_0.8Fe₂O₄, as shown in Fig. 4 (b), show two strong emission peaks at 424 and 440 nm upon excitation with a wavelength of 350 nm. The distinctive near-band-edge (NBE) blue emission, which is mainly caused by direct recombination of electrons trapped in oxygen vacancies with photogenerated holes, is shown by strongest and broadest peak at 424 nm [33–37]. Furthermore, interstitial zinc-related defect states are linked to lower-wavelength peak at 409 nm [38]. Debnath et al. reported PL emission at 409 and 430 nm for Zn_0.5Mn_0.5Fe₂O_4, which is consistent with our findings [39].

Figure 5 (a-d) shows the XPS spectra of nano-ferrite Zn_0.2Mn_0.8Fe₂O₄. Binding energy levels are examined to identify elements in s nano-ferrite, as they vary depending on the component. The scanning of the nano-ferrite displays the existence of elements such as zinc, manganese, iron, and oxygen. The detailed Mn 2p high-resolution spectrum for Zn_0.2Mn_0.8Fe₂O₄ is illustrated in Fig. 5(a). Mn 2p XPS spectra demonstration 2 main peaks, one is 2p_3/2 at 643.8 eV, and the other is 2p_1/2 at 655.4 eV. Mn 2p spectra of the peak position were fitted with a Lorentzian-Gaussian model [40]. There is no satellite peak seen between Mn 2p_3/2 and Mn 2p_1/2. This offers convincing evidence for the absence of manganese in the Mn²⁺ state at surfaces [41]. Figure 5 (b) displays high-resolution Zn 2p spectra of nano-ferrite Zn_0.2Mn_0.8Fe₂O₄. Two peaks for Zn 2p_3/2 and Zn 2p_1/2 are found, with binding energy values of 1023.16 eV and 1047.24 eV, suggesting attendance of Zn²⁺ ions [42]. High-resolution Fe 2p spectra of nano-ferrite Zn_0.2Mn_0.8Fe₂O₄ are displayed in Fig. 5 (c). XPS spectra indicate 2 peaks for Fe 2p_3/2 and Fe 2p_1/2, with binding energies of 714.4 eV and 728.2 eV, correspondingly. Figure 5 (d) depicts the O1_S high-resolution spectra of nano-ferrite Zn_0.2Mn_0.8Fe₂O₄ matched with the Lorentzian Gaussian model. There are 2 significant peaks for O1S, with binding energies of 534.78 eV and 532.54 eV. The 532.54 eV peak agrees with metal cations that are doubly linked to metal-oxygen atoms. The peak at 532.96 eV agrees with a cation that is covalently linked with 2 atoms [40]. Overall, the XPS study supports the development of a chemically stable spinel structure by confirming the anticipated elemental composition and oxidation states.

The M–H hysteresis loops of the nano-ferrite Zn_0.2Mn_0.8Fe₂O₄ measured at 300 K are revealed in Fig. 6. The sample has a tight hysteresis loop, a low coercive field (Hc ~ 0.06 kOe), a tiny remanent magnetization (Mr ≈ 5.8 emu/g), and a saturation magnetization (Ms) of about 53.21 emu/g. The hysteresis behavior is insignificant because the values of Hc and Mr are sufficiently minimal in relation to the applied magnetic field and Ms, as seen in the inset of Fig. 6. As a result, magnetic particles fall under category of soft magnetic materials. The squareness ratio of residual magnetization and saturation magnetization (Mr/Ms) is 0.10. The presence of magnetic dipole interaction with random direction and many magnetic domains in the nanoparticles is indicated by the square ratio's value being less than critical threshold of 0.5. Compared to bulk manganese ferrite (80emu/g), this high-saturation magnetism is still lower [43]. The comparatively low magnetism of nanoparticles has been explained by a number of ideas, including surface effects, spin-canting phenomenon, purity, and particle size effects [44]. Magnetic moment (µ) in Bohr magneton (µ_B) is computed from saturation magnetization data using the following relation [45];

where M_w stands for the molecular weight of the nano-ferrite. The magnetic moment value of the nano-ferrite is 2.19 µ_B.

Figure 6. Room temperature Magnetic hysteresis loop of nano-ferrite Zn0.₂Mn_0.8Fe₂O₄.

The following equation was used to compute the real and imaginary parts of impedance Z′(v) and Z′′(ν) of nano-ferrite at various temperatures:

Where ν represents applied frequency. Figure 7 illustrate Nyquist plots of typical complex impedance spectra of nano-ferrite Zn_0.2Mn_0.8Fe₂O₄ at various temperatures. In Fig. 7, impedance plots for the temperature range of 423–523 K show that the depressed semicircular arc corresponds to the high-frequency zone, while the inclined straight-line tail emerges in the low-frequency region, indicating diffusion-controlled behaviour. In Fig. 7, impedance plots of the temperature range of 548–673 K show that at high frequencies, the curve begins near the origin and rises abruptly, forming the first segment of the semicircle. At low frequencies, the spectra move away from the apex of the semicircle and toward larger Z′ values, indicating slower polarization processes. Murugesan et al. have investigated the impedance properties of zinc substitution in MnFe₂O₄ and revealed that the dielectric and conductivity values decrease with Zn substitution, indicating semiconducting properties. In contrast, the impedance findings demonstrate a dominating grain-boundary resistance.

Total conductivity (σ_t) of nano-ferrite was determined using tailored values R, d, and A, where d is thickness of the pellets, and A is electrode area. At 150°C, Zn_0.2Mn_0.8Fe₂O₄ conductivity ranges from 2.36×10^− 7 S/cm to 7.25×10^− 5 S/cm at 400°C, representing a factor of around 44. Figure 7 (a) shows total conductivity against inverse temperature for Zn_0.2Mn_0.8Fe₂O₄. The Arrhenius equation well represents the temperature-dependent total conductivity.

) (7)

σ₀ represents pre-exponential factor, T is absolute temperature, E_A is activation energy, and k_B is the Boltzmann constant. The σ₀ and E_A values are determined based on the fits shown in Fig. 7(b). The E_A of Zn_0.2Mn_0.8Fe₂O₄ is 0.59 eV with a magnitude of σ₀ = 0.50. The characteristic frequency-dependent conductivity, σ (ν), for Zn_0.2Mn_0.8Fe₂O₄ at different temperatures is revealed in Fig. 7(a). These characteristics can be seen in the σ (ν) spectra: Conductivity is nearly frequency-independent at low frequencies in low-temperature zone, indicating that ions undertake uncorrelated random hopping motions.

Figure 7. (a) Frequency-dependent behaviour of real part of ac conductivity of Zn_0.2Mn0.8Fe₂O₄ measured at different temperatures with NLLS fitting (black line). (b) Arrhenius plots for electrical conductivity of nano-ferrite Zn_0.2Mn0.8Fe₂O₄.

In the low-temperature area, conductivity is nearly frequency-independent at low frequencies, indicating that ions contribute to the dc conductivity through uncorrelated random hopping motions. A dispersion in AC conductivity is shown as νⁿ, where n < 1, when the frequency crosses over the hopping frequency ν_p [46, 47]. It is implied by this dispersive conductivity that ions move forward and backwards in a linked manner. The Almond-West conductivity formalism is utilized to suit the s nano-ferrite AC conductivity behavior and is revealed in Fig. 7(a) for Zn_0.2Mn0.8Fe₂O₄.

The DC conductivity, hopping frequency, and n parameters are obtained by NLLS fitting methods. The fitted and values increase as temperature increases. Frequency exponent n ranges is between 0.72 and 0.86, regardless of temperature. Conductivity statistics reveal dispersion in low-frequency band as temperature increases due to ion-blocking electrode effects. This is consistent with Nyquist impedance spectra.

Figure 8. Frequency-dependent dielectric constant nano-ferrite Zn0.₂Mn_0.8Fe₂O₄ at different temperatures (b) Frequency-dependent tan δ of nano-ferrite Zn0.₂Mn_0.8Fe₂O₄ at different temperatures.

Figure 8 (a) illustrates the frequency-dependent behavior of the relative permittivity (dielectric constant, ε′) of nano-ferrite Zn_0.2Mn_0.8Fe₂O₄. The dielectric constant () is derived using the following formula [48]:

Dielectric constant exhibits a decreasing trend as the frequency increases, which is related to interfacial polarization or space charge growth at electrode-nano-ferrite interface, also known as electrode polarization. Similar tendencies have been documented in the literature and are effectively described by the Maxwell–Wagner dielectric model [49, 50]. This frequency dependency of can be attributed to the involvement of several polarization mechanisms, each working principally within a certain frequency range. These include space charge (P_s), dipolar (P_d), ionic (P_i), and electronic (P_e) polarization mechanisms [51]. All these mechanisms contribute to the overall dielectric constant at low frequencies. However, with increasing frequency, the slower mechanisms (P_s, P_d) become inactive, leaving only the faster ones (P_i and P_e), leading to the observed decrease in ε′. At very high frequencies, only electronic polarization dominates due to its shortest relaxation time [52]. Koop's phenomenological theory further explains that dielectric solids consist of conducting grains separated by resistive grain boundaries [53]. At low frequencies, the dielectric response is predominantly ruled by grain boundary belongings, resulting in enhanced permittivity values. In contrast, intrinsic response of grains at higher frequencies —characterized by lower dielectric contributions—becomes dominant, leading to a decrease in the overall dielectric constant [54]

Dielectric loss is an important property that indicates how much energy a material loses when subjected to an electromagnetic wave. The value tan δ (tangent loss) [55] indicates how much the material's internal polarization lags behind the external electric field. In Fig. 8(b), tan δ changes with frequency at 423–673 K for nano-ferrite Zn_0.2Mn_0.8Fe₂O₄ exhibiting normal dispersion behavior. At low frequencies, the nano-ferrite tan δ values decline considerably. However, at high frequencies, it becomes nearly steady and does not vary significantly with frequency. However, at high frequencies, it becomes nearly steady and does not vary significantly with frequency. This trend is consistent with a recognized conduction mechanism known as the quasi-DC (QDC) process, in which the dielectric loss increases at low frequencies without presenting a visible peak or levelling out. Nano-ferrite Zn_0.2Mn_0.8Fe₂O₄ does not show any peaks. These materials' dielectric loss behavior is most likely due to a QDC-type conduction mechanism.

In summary, the eco-friendly, simple, and scalable sol-gel method was successfully employed to synthesize the nano-ferrite Zn_xMn_1-xFe₂O₄ (where x = 0.2). The development of face-centred cubic spinel structure with the (Fd3̅m) space group, with secondary phase α-Fe₂O₃ phase was confirmed by XRD analysis. FE-SEM and HR-TEM analysis revealed rod-like, agglomerated particles, while XPS confirmed the presence of Zn²⁺, Mg²⁺, and Fe²⁺ oxidation states. Raman investigation of nano-ferrite confirms the distinctive spinel modes (T₂g, Eg, A₁g), which match the given results. PL spectra indicate intense blue emissions due to oxygen-vacancy recombination and interstitial Zn defects, which is consistent with previous research. Zn_0.2Mn_0.8Fe₂O₄ has soft-magnetic behavior with low coercivity, squareness ratio, and lowered magnetization, which is consistent with normal nanoparticle effects. Dielectric investigations reveal that interfacial polarization causes substantial frequency dispersion, with permittivity rising at higher temperatures due to thermally induced dipole relaxation. AC conductivity confirms semiconducting nature; however, impedance analysis identifies grain boundaries as the primary resistive component.