177 © 2025 The Author(s). Published by the College of Education for Pure Science (Ibn Al-Haitham), University of Baghdad. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International License Sensing and Magnetic Properties in Zn-CdFe2O4 Spinel Ferrite Doped with SnO2 Prepared by Sol-Gel Auto Combustion Mariam O. Abd Alkareem 1 and Tagreed M. Al-Saadi 2* 1,2 Department of Physics, College of Education for Pure Sciences (Ibn Al-Haitham), University of Baghdad, Baghdad, Iraq. *Corresponding Author. Received: 30 January 2024 Accepted: 23 April 2025 Published: 20 July 2025 doi.org/10.30526/38.3.40788 Abstract The sol-gel method was used in this study to create the Zn-CdFe2O4/SnO2(0.15) nano ferrite, and XRD, FE-SEM, and EDX methods were used to evaluate the nano ferrite's characteristics. The findings showed that the lattice constant of the sample CdFe2O4/SnO2(0.15) is higher than that of ZnFe2O4/SnO2(0.15) and Zn0.5Cd0.5Fe2O4/SnO2(0.15) and that the resultant compound possesses a cubic spinel ferrite phase. The crystal size was on the nanoscale, according to Scherrer-Williamson Hall. Based on the FE-SEM images, it can be noticed its shape as semi-spherical or spherical; the presence of elements Zn, Cd, Fe, Sn, and O was confirmed by the EDX test. The gas sensing showed good sensitivity to NO2 gas and a short response and recovery time (15.3 sec, 49.5 sec). The magnetic properties were calculated using a vibrating sample magnetometer, where soft magnetic behavior was shown for all samples. The novel zinc cadmium ferrite preparation is expected to find use in a wide range of products, including biomedical equipment, motors, sensors for high-density data storage devices, and magnetic recording devices. Keywords: Zn-Cd ferrite, Doped SnO2, NO2 gas, Sensitivity, Recovery time, Magnetic properties. 1. Introduction There is growing interest in discovering novel materials to create solid-state gas sensors with great performance. Semiconductor metal oxide sensors are a reliable and affordable substitute for conventional detection methods. MFe2O4 spinel-type oxide semiconductors are materials that are sensitive to reducing and oxidizing gases (1). NO2 is regarded as hazardous to both human health and the environment. Thus, the creation of sensors to identify NO2 gas is crucial (2) Nowadays, scientists are focused on ferrite materials due to their special physical characteristics, such as their optical, electrical, and magnetic because of their many uses in devices with low and high permeability, ferrofluids, microwaves, high-density storage devices, and magnetic drug delivery, ferrites are being studied for their gas detecting capabilities. A mixture of iron and metal oxides is called ferrite. ferrite exhibits ferrimagnetic properties, high electrical resistance, and dielectric behavior. Ferrites were divided into four categories: granites, orthoferrites, spinels, and https://orcid.org/0009-0003-0574-6020 mailto:Mariam.Abd2204p@ihcoedu.uobaghdad.edu.iq https://orcid.org/0000-0002-8275-3748 mailto:taghreed.m.m@ihcoedu.uobaghdad.edu.iq https://orcid.org/0009-0003-0574-6020 mailto:Mariam.Abd2204p@ihcoedu.uobaghdad.edu.iq https://orcid.org/0000-0002-8275-3748 mailto:taghreed.m.m@ihcoedu.uobaghdad.edu.iq https://orcid.org/0009-0003-0574-6020 mailto:Mariam.Abd2204p@ihcoedu.uobaghdad.edu.iq https://orcid.org/0000-0002-8275-3748 mailto:taghreed.m.m@ihcoedu.uobaghdad.edu.iq https://orcid.org/0009-0003-0574-6020 mailto:Mariam.Abd2204p@ihcoedu.uobaghdad.edu.iq https://orcid.org/0000-0002-8275-3748 mailto:taghreed.m.m@ihcoedu.uobaghdad.edu.iq https://orcid.org/0009-0003-0574-6020 mailto:Mariam.Abd2204p@ihcoedu.uobaghdad.edu.iq https://orcid.org/0000-0002-8275-3748 mailto:taghreed.m.m@ihcoedu.uobaghdad.edu.iq https://orcid.org/0009-0003-0574-6020 mailto:Mariam.Abd2204p@ihcoedu.uobaghdad.edu.iq https://orcid.org/0000-0002-8275-3748 mailto:taghreed.m.m@ihcoedu.uobaghdad.edu.iq IHJPAS. 2025, 38(3) 178 hexagonal. Large magnetocrystalline anisotropy, high Ms, high curie temperature, and Hc were among the several characteristics displayed by spinel ferrite (3,4). The ferrite's metal created a divalent bond. 32 Oxygen atoms make up the unit cell in the cubic structure of spinel ferrite, which is composed of closely packed oxygen atoms. A) tetrahedrally coordinated sites, which are covered by four oxygen atoms, and B) octahedrally coordinated sites, which are covered by six oxygen atoms, are the two kinds of sites between anions that have an FCC face-centered cube configuration (5). Ferrite nanoparticles have been synthesized by a variety of chemical processes. These techniques include sol-gel (6), chemical co-precipitation (7), and micromulsion (8). Among these techniques, the sol-gel approach is frequently employed to create ferrite nanoparticles. The ratio of metal nitrates to fuel, speed, stirring duration, pH, and fuel can all have a significant impact on the size and characteristics of spinel ferrite nanoparticles (9). Mehrfar et al. synthesized spinel ferrite MFe2O4 (M=Cd, Zn, Co) nanoparticles using the sol- gel method. The impact of metal M on linalool gas sensing performance was examined, and the findings showed that nano-CdFe2O4 is a viable gas detection option suggesting its potential utility in sensor manufacturing (10). Rezlescu et.al generated some spinel ferrite by spontaneous combustion of sol-gel and their gas-sensing properties were investigated. It was found from this study that ZnFe2O4 is sensitive and selective to ethanol (11). The series (Co0.2 Zn0.8-x Cdx Fe2O4) with (x=0, 0.3, 0.6) was prepared by rapid spontaneous combustion method and heated for two hours to 800°C. Magnetism was measured using a vibrating sample magnetometer (VSM). The nanoparticles were found to be soft magnetic materials since the hysteresis loop was minimal (12). The current study investigates the effect of the nano ferrite compound Zn-CdFe2O4/SnO2(0.15) on structure, sensing to NO2 gas, and magnetic properties. 2. Materials and Methods Zn-CdFe2O4/SnO2(0.15) with a weight ratio of SnO2 (0.15), Table (1) lists the masses of raw ingredients needed to prepare ferrite, which was made using the sol-gel process. The metal nitrates are weighed and then dissolved in tiny volumes of distilled water. Using a magnetic stirrer, this solution is mixed with citric acid to form a homogeneous mixture. Drops of ammonia are added after mixing to reach the pH (~7). For an hour, the solution is heated to 80°C while being constantly stirred. After that, the solution is left to evaporate and stays at this temperature until it gels. Following that, the temperature is raised even higher to 110°C. At this point, the gel begins to dry when the temperature reaches 120°C, and the dry gel begins to ignite. After obtaining the resultant ferrite, each sample’s combustion products are allowed to cool before being calcined in an oven set at 600°Cfor two hours. Table 1. The masses of raw materials to produce Zn-CdFe2O4/SnO2(0.15) Sample Composition Ferric Nitrate Zinc Nitrate cadmium Nitrate Tin chloride Citric acid n m(g) n m(g) n m(g) w m(g) n m(g) M1 ZnFe2O4/ SnO2(0.15) 2 32.32 1 11.8996 0 0 0.15 1.7849 3 23.056 M2 CdFe2O4/ SnO2(0.15) 2 32.32 0 0 1 12.3392 0.15 1.8509 3 23.056 M3 Zn0.5Cd0.5Fe2O4 /SnO2(0.15 2 32.32 0.5 5.9498 0.5 6.1696 0.15 1.8179 3 23.056 IHJPAS. 2025, 38(3) 179 3. Results and Discussion 3.1. X-ray diffraction analysis An X-ray diffraction (XRD) analysis was performed to determine the composition of the Zn- Cd Fe2O4/SnO2 phase in the range (20° ≤ 2θ ≤ 80°). A cubic spinel structure type FCC (13) with planes [ (220), (311), (222), (400), (422), (511), (440) and (533)] is confirmed by the indexed x-ray diffraction patterns of Zn0.5Cd0.5Fe2O4/SnO2 which are displayed in figure 1. The diffraction values agree with the card numbers (no.22-1012), and (no.22-1063). Lattice parameters were calculated using (Match! software) and the Scherrer equation was used to get the mean crystallite size (14, 15). Dsh = 0.9λ/βcosθ (1) Where D is the crystallite size, λ is the X-ray wavelength (1.54 Å), β is the full width at half maximum and θ is the incidence angle. The following equation’s x-ray density must be calculated (16): ρ=8Mw /NA. a 3 (2) Where (MW) is the molecular weight, (NA) is the number of the Avogadro and (a) is the lattice constant Figure 1. X-Ray diffraction of the Zn-CdFe2O4/SnO2(0.15) nano-ferrite. Table (2) demonstrates that the CdFe2O4/SnO2(0.15) sample’s lattice constant is greater than the ZnFe2O4/SnO2(0.15), Zn0.5Cd0.5Fe2O4/SnO2(0.15) sample's, the reason for this is that cadmium ionic radius(92pm) is greater than zinc ionic radius (47pm). The lattice constant rises when the cadmium ion enters the lattice or is positioned between host ions. This aligns with the researcher's findings (17) However, table2 illustrates that the crystallite size, as calculated by Scherrer equations, is at the nanoscale. We also used the Williamson-Hall to calculate the grain size (18,19) βhkl =(Kλ/D) +4ε sinθ (3) where K: is constant, λ: is the Cu kα radiation wavelength, D: the average grain size, and ε: is the microstrain, the equation is plotted with sin θ on the x-axis and β cos θ on the y-axis for all samples to determine the average crystallite size and strain from the slope (the intercept Kλ/D and the 4ε) and y-axis intercept of the fitted line as shown in Figure 2 according to the Williamson-Hall, according to Table 2 , the microstrain for ZnFe2O4/SnO2(0.15) , Zn0.5Cd0.5Fe2O4/SnO2(0.15) positive and for CdFe2O4/SnO2(0.15) is negative .This is explained by the fact that the transfer of iron ions between the octahedral and tetrahedral positions who created flaws in the magnetic nano oxide's structure that caused the sample's lattice to contract (20). IHJPAS. 2025, 38(3) 180 Figure 2. Williamson-Hall analysis of Zn-CdFe2O4/SnO2(0.15) nanoparticles. Table 2. Lattice constants, crystallite size and density of Zn-CdFe2O4/SnO2(0.15) nano-ferrite. Microstrain ε * 10 -3 D W-H (nm) D Sch. (nm) Density (g/cm 3 ) Lattice constant (Å) samples 4.275 66.9 27.54 5.324 8.4418 M1 -3.35 10.8 28.33 6.249 8.7003 M2 2.101 4.27 26.46 6.108 8.4926 M3 3.2. Morphological analysis The samples of the generated compound (Zn-CdFe2O4/SnO2(0.15)) were photographed using the emission field scanning electron microscopy (FE-SEM) technique. It has been verified that the material is in the nanoscale region, as seen in Figure (3), it was observed that the particles had a spherical or semi-spherical form with some gaps and gatherings: this suggests that the compound is porous, which enhances the sensor's reaction to the gas (21). 3.3. Elemental analysis EDX was used to analyze the samples produced using the auto-combustion process. The elements Fe, Zn, Cd, Sn, and O are represented by the observed peaks, which show that the Zn0.5Cd0.5Fe2O4/SnO2(0.15) sample's components have been examined in Figure 4 EDX spectra. Demonstrating that the auto combustion (sol-gel) technique creates oxides with a high degree of elemental similarity (22, 23). 3.4. Sensing Properties The powder was compressed at a pressure of 1.5t/cm 2 using a manual press. After that, the 1cm in diameter and 3.5 mm thick pellets were heated for two hours at 900°C. After that, they were automatically left to cool and heat in the oven. The electrodes for the samples were then made. The sensitivity of each sample to NO2 gas across the specified temperature range (200°C, 250°C, and 300°C) was ascertained using gas sensitivity test equipment. At the concentration, the gas is 129.18pm (Figure 5). IHJPAS. 2025, 38(3) 181 Figure 3. FE-SEM of Zn-CdFe2O4/SnO2(0.15) ferrite nanoparticles samples. Figure 4. EDX of the nano ferrite samples Zn-CdFe2O4/SnO2(0.15) M1 M2 M3 M1 M2 M3 IHJPAS. 2025, 38(3) 182 Figure 5. The relationship between sensitivity and operating temperature of Zn-CdFe2O4/SnO2(0.15) Table (3) shows the maximum sensitivity values for the Zn-CdFe2O4/SnO2(0.15) samples, and it is noteworthy that the maximum sensitivity value was at 250 °C. Table 3. The highest sensitivity values of the NO2 gas for Zn-CdFe2O4/SnO2(0.15) nanoparticles. Highest sensitivity value (%) Operating Temperature Samples 228.409 200°C M1 21.315 300°C M2 324.390 250°C M3 The sensitivity of Zn-CdFe2O4/SnO2(0.15) samples to the oxidizing nitrogen gas (NO2) was investigated, and it was found that all samples were sensitive to NO2, enabling its usage in a variety of applications because of Zn0.5Cd0.5Fe2O4/SnO2(0.15) combination contains zinc, cadmium, and tin together, it has the lowest particle size, as seen in Table (2), and it can find that it had the best sensitivity at 250°C. Therefore, a tiny particle size is linked to a compound's higher sensitivity (24). The tin element can improve the distribution of pore sizes, specific surface area, and porosity. More surface area indicates more active sites for NO2 gas, which raises the sensitivity of gas sensors (25). The response and recovery time of nano ferrite Zn-CdFe2O4/SnO2(0.15) exposed to NO2 gas are displayed in Table (4). Sample Zn0.5Cd0.5Fe2O4/SnO2(0.15) had the shortest response time (15.3 sec), and sample ZnFe2O4/SnO2(0.15) had the shortest recovery time (49.5 sec). This is because of the sol-gel process and its significant advantages, which include increased homogeneity, high purity, more uniform phase distributions in multi-component systems, and the potential to create novel nanophases (26). IHJPAS. 2025, 38(3) 183 Table 4. Minimum response and recovery time for Zn-CdFe2O4 / SnO2(0.15) samples to NO2 gas. Operating Temperature (°C) Minimum recovery Time (s) Operating Temperature (°C) Minimum response Time (s) Samples 300°C 49.5 250°C 19.8 M1 250°C-300°C 54 200°C 16.2 M2 250°C 62.1 300°C 15.3 M3 3.5. Magnetic properties: Figure (7) displayed the magnetic hysteresis ring, size, and shape of each of the Zn- CdFe2O4/SnO2(0.15) sample’s ferrite nanoparticles as determined by the vibration magnetic device (VSM) The composition of ferrite is the other factor that affects the rate at which cations diffuse in the solid state during sintering (27). To react to gases, ferrite sensors need to be thermally excited. The best response and recovery time is obtained at the optimum operating temperature 300°C (Figure 6). Table (4) demonstrates that samples of the produced compound had a minimum response time for NO2 gas at operating temperature (300°C) and a minimum recovery time at operating temperature (300)°C. Figure 6. Relationship of recovery time and response time of NO2 gas at operating temperature of Zn- CdFe2O4/SnO2(0.15) samples, where the blue line indicates response time, while the red line indicates recovery time. The illustration (magnetic hysteresis loops) of nano ferrite is shown in Figure (7). Because of its tiny size, it has a soft magnetic nature. The tiny crystal size was demonstrated by examining XRD in Table 2 (28), where earlier research verified that super magnetism is displayed by nanoparticles with a size less than 30nm or less than the critical size of the magnetic field (29, 30), The small and narrow hysteresis ring size significantly influenced by magnetic characteristics. Shape and width of the hysterical loop are influenced by the IHJPAS. 2025, 38(3) 184 chemical content (31). The findings show that the magnetic characteristics of ferrite are altered by variations in the concentration of zinc and cadmium (32). Figure 7. The relationship between magnetism and the applied field of Zn-CdFe2O4/SnO2(0.15). Cd Ferrite is a strong contender for use as soft magnets and low-loss materials at high frequencies due to its outstanding electromagnetic performance, exceptional chemical stability, low coercive force, and mild saturation magnetization (33). Zinc causes lower crystalline magnetic anisotropy compared to Cd (17). Tiny may be added to samples to increase their magnetic (34) since SnO2 is an n-type semiconductor with a wide energy gap Eg=3.6 eV (35) since the nanoparticles functioned as monopole particles causing a coherent spin magnetization reversal(36), because of variation in the lattice site configurations, crystal structures, particle compositions, and sizes the computed differences between Ms, Mr, and Hc (37, 38). Hc is the lowest for the ZnFe2O4/SnO2(0.15) and greatest for Zn0.5Cd0.5Fe2O4/SnO2(0.15) has Zn/Cd ratio 50/50, this is consistent with researchers' findings (17). Table 5. Magnetic factor variation for ZnCdFe2O4/SnO2(0.15) nanoparticles. Compound Ms(emu/g) Mr(emu/g) Hc (Oe) ZnFe2O4/SnO2(0.15) 1.02 0.04 17.10 CdFe2O4/SnO2(0.15) 2.71 0.47 60.54 Zn0.5Cd0.5Fe2O4/SnO2(0.15) 0.41 0.02 610.39 4. Conclusion Sol-gel synthesis was used to create Zn-CdFe2O4/SnO2(0.15) nano ferrite. The lattice constant of the sample CdFe2O4/SnO2(0.15) was higher than of the sample ZnFe2O4/SnO2(0.15), Zn0.5Cd0.5Fe2O4/SnO2(0.15), according to x-ray diffraction. Using Scherrer and Williamson- Hall analysis, we determined the grain size. The semi-spherical or spherical grains with some clusters and gaps in the scanning electron microscope (FE-SEM) pictures indicate the compound's nature and improve the sensor's responsiveness to gas. The sample recorded the highest sensitivity at the operating temperature of 250°C and the shortest response and recovery time at the temperature of 300°C. The nano ferrite exhibits good sensitivity to NO2 IHJPAS. 2025, 38(3) 185 at various temperatures. Using a hysteresis loop, the generated sample's soft magnetic nature was verified, where the results showed the Hc value was the highest for the sample Zn0.5Cd0.5Fe2O4/SnO2(0.15). Acknowledgment I would like to thank the staff of the Physics Department, Deanship of the College of Education for Pure Science (Ibn Al-Haitham), for their support in writing this research. Conflict of Interest The authors declare that they have no conflicts of interest. Funding None. References 1. Rossinyol E, Arbiol J, Peiró F, Cornet A, Morante JR, Tian B, Bo T, Zhao D. Nanostructured metal oxides synthesized by hard template method for gas sensing applications. Sens Actuators B Chem 2005;109(1):57–63. https://doi.org/10.1016/j.snb.2005.03.016 2. Kadhim GA, Mohammed MA. Effect of the chloroform as a chemical treatment on gas sensing for cupcts/alq3 thin films. Dig J Nanomater Biostruct 2021;16(1). 3. Lassoued A, Lassoued MS, Karolak F, García-Granda S, Dkhil B, Ammar S, Gadri A. 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