Zinc substitution effect on the structural, spectroscopic and electrical properties of nanocrystalline MnFe2O4 spinel ferrite.

This paper reports the structural, morphological, spectroscopic, dielectric, ac conductivity, and impedance properties of nanocrystalline Mn1-xZnxFe2O4. The nanocrystalline Mn-Zn ferrites were synthesized using a solvent-free combustion reaction method. The structural analysis using X-ray diffraction (XRD) pattern reveals the single-phase of all the samples and the Rietveld refined XRD patterns confirmed the cubic-spinel structure. The calculated crystallite size values increase from 8.5 nm to 19.6 nm with the Zn concentration. The surface morphological analysis using field emission scanning electron microscopy and the transmission electron microscopy confirms the nano size of the prepared ferrites. X-ray photoelectron spectroscopy was used to study the ionic state of the atoms present in the samples. Further, the high-resolution Mn 2p, Zn 2p, Fe 2p, and O 1s spectra of Mn1-xZnxFe2O4 does not result in the appearance of new peaks with Zn content, indicating that the Zn substitution does not change the ionic state of Mn, Zn, Fe, and O present in nanocrystalline Mn1-xZnxFe2O4. The investigated electrical properties show that the dielectric constant, tan δ and ac conductivity gradually decrease with increasing Zn substitution and the sample Mn0 · 2Zn0 · 8Fe2O4 has the lowest value of conductivity at 303 K. The ac conductivity measured at different temperatures shows the semiconducting nature of the ferrites. The impedance spectra analysis shows that the contribution of grain boundary is higher compared with the grain to the resistance. The obtained results suggest that the Zn substituted manganese ferrite nanoparticles can act as a promising candidate for high-frequency electronic devices applications.

Introduction

Nanomaterials with dimensions of 1 nm–100 nm show paradigm change in chemical, physical, electrical, magnetic, and optical properties compared with its bulk counterpart [[1], [2], [3], [4], [5], [6]]. The ultimate goal of nanoscience is to exploit these unusual properties to develop next-generation devices. Based on the area of application, the field of nanoscience has expanded and rechristened as nanoelectronics, nanomagnetism, nanophotonics, and nanomechanics [[7], [8], [9]]. In the field of nanomagnetism, the spinel ferrites are important materials because they exhibit unusual magnetic and electrical properties in comparison with their bulk counterpart [4,[10], [11], [12]]. Nanocrystalline spinel ferrites have been demonstrated as useful material for hyperthermia [13,14], detection of COVID-19 [15], visible light-enabled photodegradation [16] and, the catalyst for the synthesis of chalcones [17]. The molecular formula of spinel-type ferrite is MFe2O4 (M = Co, Ni, Mn, Mg, or other divalent cations) [18]. Two types of interstitial sites exist such as tetrahedral site coordinates 4 surrounding O ions and the octahedral site coordinates 6 surrounding O ions [19]. The important properties of ferrites are determined by the distribution of cations within these interstitial sites. Depending on the occupancy of divalent cations and the Fe3+ ions in interstitial sites, the spinel ferrites are generally categorized as normal, inverse, and mixed. Among these three types, mixed ferrites are considered significant materials because of their wide range of tunability in properties. In recent decades, several investigations have been done to explore and enhance the magnetic and electrical properties of end member ferrites by substituting different divalent and trivalent cations using various synthesis methods [16,[20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34]]. Among the spinel ferrites, the Zn substituted ferrites are attracted special interest due to the strong tetrahedral site preference of Zn2+ ion. Choodamani et al. [25] prepared the Zn substituted MgFe2O4. The evaluated crystallite sizes were in the range of 47–80 nm. The dielectric constant, tan δ, and electrical conductivity were the lowest for x = 0.50 sample. The saturation magnetization of the ferrites increases up to x = 0.5 with the Zn concentration. In our previous work, we investigated the nanocrystalline Cu1-xZnxFe2O4 mixed ferrites. The size of the crystallites was in the range of 9.6–31 nm. The magnetization of the samples increases up to x = 0.2 (44.16 emu/g). The prepared ferrites exhibit superparamagnetic behavior for x ≥ 0.4 concentration of Zn [35]. Andhare et al. [27] prepared the Co1-xZnxFe2O4 mixed ferrite nanoparticles. The crystallite size, lattice constant, and X-ray density were increases with zinc substitution. The energy band gap of prepared ferrites was increasing from 2.258 eV to 2.8306 eV. The hysteresis curve of ferrites shows that the prepared ZnFe2O4 was magnetically softer than CoF2O4. Anupama et al. [29] synthesized the nanocrystalline Ni1-xZnxFe2O4 samples through the combustion technique. The cubic structure of the prepared sample without the formation of impurity phases was confirmed using Rietveld refinement. The magnetic properties reveal that the highest value of magnetization obtained for x = 0.4. It is observed from the literature results that the Zn substitution significantly improves the properties of Mg, Cu, Co, and Ni based nano ferrites. Among the number of spinel-type ferrites, manganese ferrite (MnFe2O4) is an attractive ferrite with important applications in catalysis [36,37], gas sensor [38], MRI contrast agents [39], hyperthermia [40], transformer core [41,42], deflection yokes [43], and microwave device [44,45] because of the high value of magnetization and resistivity. The bulk MnFe2O4 is crystallized in cubic symmetry with Fdm space group, in which 80% of Mn ions occupy the A sites, and 20% occupy the B sites [46]. Over the past few decades, researchers focused on the synthesis of various nano ferrites to explore the novel properties. The synthesis method and synthesis parameters have an important impact on the size of the particles which subsequently results into the change in properties for the same ferrite [32,47,48]. Since different synthesis methods yield different magnetic and electrical properties, in this work a simple and low-cost solvent-free synthesis method is used to synthesize nano-sized Zn substituted MnFe2O4 with the chemical formula of Mn1 - xZnxFe2O4. The advantage of this synthesis route is that it does not involve any solvent to dissolve the precursor. Since the metal nitrates used during the synthesis are hygroscopic in nature, they tend to form a homogeneous mixture so that the solvent evaporation time can be minimized. The total synthesis process completed within an hour. In our previous investigation the structural and magnetic properties of the same compounds were reported [28]. In this work, the structural, morphological, spectroscopic, dielectric, ac conductivity, and impedance properties of the Mn–Zn ferrites were systematically studied and the obtained results are discussed in detail in the following sections.

Experimental details

Synthesis

Nanocrystalline Mn1−xZnxFe2O4 (where x = 0.0 to 1.0 in steps of 0.2) ferrites were synthesized through a solvent-free combustion reaction method. To synthesize Mn1−xZnxFe2O4, nitrates of manganese, zinc, iron, and citric acid were used as precursor materials. The reactants were weighed and then mixed for 30 min using a magnetic stirrer. Then the nitrate and citric acid mixture were heat-treated at 75 °C until it forms a dry gel. Since the metal nitrates are hygroscopic in nature, the mixed metal nitrates form gel during mixing. The obtained dried gel was heated continuously until self-combusted. The resultant ferrite powder was heat-treated for 1 h at 300 °C and then used for further characterization [28,49].

Characterization

The X-ray diffraction (XRD) pattern of the ferrites was recorded using a powder X-ray diffractometer (Ultima IV, RIGAKU) by employing Cu-Kα1 (Wavelength-1.5406 Å) radiation. Rietveld refinement was carried out using the GSAS program and its EXPGUI user interface. The surface morphology image of the ferrites was examined using Carl Zeiss SUPRA 55 field emission scanning electron microscope (FE-SEM). Particle morphology was obtained using transmission electron microscopy (TEM) observations using a JEOL JEM-2100F microscope that operates at 200 kV. The spectra of oxidation states at the surface were recorded using a Thermo Fisher ESCALAB 250xi photoelectron spectroscopy (XPS). The pass energy for a wide survey and narrow spectra is 100 eV and 30 eV, respectively. The AC electrical properties were measured using a broadband dielectric spectrometer (BDS) Alpha Analyser Concept 80, Novocontrol.

Results and discussion

X-ray diffraction analysis

The Rietveld refined powder XRD patterns of spinel Mn1-xZnxFe2O4 ferrites are shown in Fig. 1 . The broadening of diffraction peaks shows that the prepared ferrite samples are smaller sized [28]. No additional reflection peaks correspond to any secondary phase was observed in nanocrystalline Mn1-xZnxFe2O4. The values of crystallite sizes are calculated using Scherrer's formula [49] and given in Table 1 .

Fig. 1

Rietveld refined XRD patterns of Mn1-xZnxFe2O4 mixed ferrites [28].

Table 1

Crystallite size (D) and lattice constant (a) of nanocrystalline Mn1-xZnxFe2O4.

x	D (nm)	a (Å)
0.0	8.5	8.358
0.2	8.2	8.362
0.4	9.4	8.419
0.6	10.5	8.427
0.8	11.5	8.429
1.0	19.6	8.435

The size of the nanocrystalline MnFe2O4 is 8.5 nm. Moreover, no significant change in crystallite size was observed for the initial x = 0.2 substitution. For further substitution, the size of the crystallites increases slowly up to x = 0.8 and suddenly reaches to 19.6 nm for x = 1.0. This finding indicates that the Mn and Zn ratio has a major influence on the crystallites size [50]. The lattice constant values of nanocrystalline Mn1-xZnxFe2O4 are determined using the relation given in Ref. [49] and are given in Table 1. The Zn substitution increases the values of the lattice constant gradually. Nevertheless, the Zn2+ (0.74 Å) ionic radius is larger than that of the Mn3+ (0.645 Å), an increased lattice constant value is observed for Zn-substituted samples. The Rietveld refinement was carried out for all the samples and the Mn1-xZnxFe2O4 are seen to crystallize in spinel structure with the space group . The structural parameters of Mn1−ZnFe2O4 ferrites such as goodness of fit, lattice constant, bond length, bond angle, and cation occupancy obtained from the Rietveld refinement are given in Table 2 . The lattice constant values are almost similar to that of the value calculated theoretically. The bond length O–B, O-A, and the bond angle A-O-B, B–O–B, and O–B–O of MnFe2O4 are slightly affected for the Zn substituted samples which confirm the substitution of Zn. The cation occupancy in different sites also was refined and given in Table 2 which indicates the change in cation distribution with Zn concentration.

Table 2

Structural parameters of Mn1−ZnFe2O4 obtained from the Rietveld refinement of XRD patterns.

Structural parameters		x = 0.0	x = 0.2	x = 0.4	x = 0.6	x = 0.8	x = 1.0
Goodness of fit (χ2)		8.491	8.886	8.075	8.121	8.119	7.837
Lattice Constant (Ǻ)		8.334	8.349	8.403	8.418	8.436	8.438
Bond length (Ǻ)	O–B	2.0342(4)	2.0196(14)	2.0020(8)	2.0480(7)	2.0345(6)	2.0763(4)
	O - A	1.96368(30)	1.9290(10)	2.0000(6)	1.9229(5)	1.9604(4)	1.88536(25)
Bond Angle (degree)	A-O-B	122.12	122.45	121.04	123.00	122.18	123.95
	B–O–B	94.35	93.91	95.81	93.20	94.27	91.85
	O–B–O	85.48	85.95	83.88	86.71	85.56	88.12
Cation occupancy	Mn (A site)	0.8718	0.6504	0.4836	0.3251	0.1604	0
	Zn (A site)	0	0.1701	0.3196	0.4795	0.6399	0.8073
	Fe (A site)	0.2765	0.2113	0.2036	0.1992	0.1996	0.2001
	Mn (B site)	0.0942	0.0671	0.0633	0.0387	0.0194	0
	Zn (B site)	0	0.0186	0.0413	0.0599	0.0809	0.0991
	Fe (B site)	0.8895	0.8973	0.8790	0.8996	0.9055	0.8990
	O	1.0405	0.8959	0.9123	0.9370	0.9687	1.0227

Surface morphological analysis

FE-SEM analysis

The surface morphology images of Mn1-xZnxFe2O4 ferrites are shown in Fig. 2 . The images confirm the nano size of the samples, and the prepared samples are roughly spherical in shape. Furthermore, the substitution of Zn does not greatly affect the surface morphology of nanocrystalline Mn1-xZnxFe2O4 up to x = 0.8.

Fig. 2

FE-SEM images of Mn1-xZnxFe2O4 mixed ferrites.

TEM analysis

The TEM images for selected samples of Mn1-xZnxFe2O4 (x = 0.0, 0.4 and 1.0) are shown in Fig. 3 . The particles are aggregated, and the images further showed that the particles of x = 1.0 sample have bigger sizes than other samples, as observed in FE-SEM analysis.

Fig. 3

The TEM images and SAED patterns of Mn1-xZnxFe2O4 (where x = 0.0, 0.4 and 1.0) mixed ferrites.

The selected area electron diffraction (SAED) patterns of the Mn1-xZnxFe2O4 (where x = 0.0, 0.4, and 1.0) nanoparticles presented in Fig. 3 shows the concentric rings and bright spots over the rings, which point out the polycrystalline nature of the prepared ferrites. The size distribution from the TEM images was calculated and fitted for the Lorentzian shape as shown in Fig. 4 . The calculated values of particle size of the samples x = 0.0, x = 0.4 and x = 1.0 are 7.54, 8.71 and 17.73 nm, respectively. The obtained values of particle size are agreed well with the XRD results.

Fig. 4

The particle size distribution for the TEM images of Mn1-xZnxFe2O4 (where x = 0.0, 0.4, and 1.0) mixed ferrites fitted for the Lorentzian shape.

X-ray photoelectron spectroscopy analysis

The XPS wide-scan spectra of Mn1-xZnxFe2O4 nanoparticles are shown in Fig. 5 . Given that the binding energy varies for different elements, the binding energy values are used to find out the elements present in the samples. The survey scan of the samples shows the presence of elements, such as carbon, oxygen, iron, manganese, and zinc.

Fig. 5

XPS survey spectra of Mn1-xZnxFe2O4 mixed ferrite nanoparticles.

Mn 2p peak

The high-resolution Mn 2p spectra of MnFe2O4 are shown in Fig. 6 . The XPS spectra that correspond to Mn 2p shows two major peaks around 641.6 eV (Mn 2p3/2) and 653.4 eV(Mn 2p1/2) for MnFe2O4. The peak position of the Mn 2p spectra was fitted using the Lorentzian–Gaussian model [51]. No satellite peak is observed between Mn 2p3/2 and Mn 2p1/2. This provides clear evidence for the absence of manganese in Mn2+ state at the surfaces [37]. The XPS spectra of Zn substituted samples are shown in Fig. 7 . The substitution of Zn has not resulted in the emergence of new peaks, which in-turn confirms the incorporation of Zn into MnFe2O4.

Fig. 6

Mn 2p XPS spectra of nanocrystalline MnFe2O4 ferrite.

Fig. 7

Mn 2p XPS spectra of nanocrystalline Mn1-xZnxFe2O4 mixed ferrites.

Zn 2p peak

Fig. 8 shows the high-resolution Zn 2p spectra of Mn0 · 8Zn0 · 2Fe2O4 ferrite nanoparticles. The peak position of the Zn ions in Zn 2p spectra was fitted using the Lorentzian–Gaussian model and shown in Fig. 8. Two peaks for Zn 2p3/2 and Zn 2p1/2 with the binding energy values of 1021.16eV and 1044.24eV are observed, indicating the presence of Zn2+ ion [52]. Fig. 9 shows that no large change is observed in the position of the peaks implying that the ionic state of Zn remains the same for the high concentration of Zn. Furthermore, these spectra confirm that the Zn atom is fully dissolved in the spinel-structured MnFe2O4.

Fig. 8

Zn 2p XPS spectra of nanocrystalline MnFe2O4 ferrite.

Fig. 9

Zn 2p XPS spectra of nanocrystalline Mn1-xZnxFe2O4 mixed ferrite.

Fe 2p peak

The high-resolution Fe 2p spectra of MnFe2O4 nanoparticles are shown in Fig. 10 . The XPS spectra show two peaks for Fe 2p3/2 and Fe 2p1/2 with the binding energy values of 710.4 eV and 724.2 eV respectively. In addition to that two satellite peaks appear at binding energies of 718.6 and 732.7 eV, indicating the presence of Fe3+ cations [37]. The high-resolution XPS spectra of nanocrystalline Mn1-xZnxFe2O4 ferrites are shown in Fig. 11 . The substitution of Zn does not result in the appearance of new peaks, indicating that Zn does not change the ionic state of Fe present in nanocrystalline Mn1-xZnxFe2O4.

Fig. 10

Fe 2p XPS spectra of nanocrystalline MnFe2O4 ferrite.

Fig. 11

Fe 2p XPS spectra of nanocrystalline Mn1-xZnxFe2O4 mixed ferrites.

O 1s peak

Fig. 12 shows the O 1s high-resolution spectra of MnFe2O4 fitted for the Lorentzian–Gaussian model. Two major peaks for O 1s with the binding energy values of 530.78 eV and 529.54 eV are observed. The peak at 529.54 eV corresponds to the metal cations doubly bonded with metal-oxygen atoms. The peak observed at 530.78 eV corresponds to the cation that is covalently bonded to two atoms [51]. The XPS spectra of nanocrystalline Mn1-xZnxFe2O4 are shown in Fig. 13 . The substitution of Zn increases the binding energy of nanocrystalline Mn1-xZnxFe2O4 ferrites.

Fig. 12

O 1s XPS spectra of nanocrystalline MnFe2O4 ferrite.

Fig. 13

O 1s XPS spectra of nanocrystalline Mn1-xZnxFe2O4 mixed ferrites.

AC electrical properties of nanocrystalline Mn1-xZnxFe2O4

Dielectric constant

The frequency dependant dielectric constant (ε′) of nanocrystalline Mn1-xZnxFe2O4 is shown in Fig. 14 . The dielectric constant values are almost constant at lower frequencies and decreases at higher frequencies. The dielectric dispersion at the lower frequency region is due to the space charge effect that arises from the grain size, Fe2+ ions, and oxygen vacancies present in the samples [25]. The electrical conduction in the spinel arises from the charge carriers hopping between the ions, and the dielectric polarization is also explained through the same mechanism [53,54]. The dielectric polarization in MnFe2O4 is attributed to the hopping of electron between Fe2+↔Fe3+ and the hole hopping between Mn3+↔Mn2+ ions in the octahedral site; in ZnFe2O4, polarization arises from the hopping of electron between Fe2+↔Fe3+ cations [12,25]. These charge carriers hopping between Fe2+↔Fe3+ ions cannot cooperate at higher frequencies with the external electric field, thereby reducing polarization [54]. The substitution of Zn decreases the dielectric constant by up to x = 0.8, and the nanocrystalline Mn0 · 2Zn0 · 8Fe2O4 sample has the lowest value. However, ZnFe2O4 exhibits a higher dielectric constant than Mn0 · 2Zn0 · 8Fe2O4 and also show slightly different dielectric relaxation behavior than the other samples. Such behavior may arise due to the presence of more number of Fe2+ ions in octahedral sites and higher grain size of the ZnFe2O4 [25].

Fig. 14

Frequency-dependent dielectric constant of nanocrystalline Mn1-xZnxFe2O4 at 303 K.

Dielectric loss tangent

Frequency-dependent dielectric loss tangent (tan δ) of nanocrystalline Mn1-xZnxFe2O4 is shown in Fig. 15 . Initially, tan δ decreases with frequency, and a relaxation peak emerges at particular frequencies. When the charge carrier's hopping frequency between Fe2+↔Fe3+ and Mn3+↔Mn2+ is larger than that of the applied field, the charge carriers able to follow the electric field, due to that more absorption occurs at lower frequencies, thereby incurring more loss. However, at higher frequencies, the hopping frequency of the charge carriers cannot follow the external field. Thus, less absorption occurs, and hence less loss is obtained. In addition to that, the dielectric loss also occurs from the dipole relaxation, which dissipates energy [55]. Relaxation peaks in tan δ arise when the charge carrier's hopping frequency is same as the frequency of the applied field. The substitution of Zn decreases tan δ, and the Mn0 · 2Zn0 · 8Fe2O4 sample has the lowest value among all the samples.

Fig. 15

Frequency-dependent tan δ of nanocrystalline Mn1-xZnxFe2O4 at 303 K.

AC conductivity

The frequency-dependent real part of ac electrical conductivity (σ′) of Mn1-xZnxFe2O4 mixed ferrites is shown in Fig. 16 . At lower frequencies, conductivity increases slowly whereas rapidly increases at higher frequencies. At lower frequencies, the resistive natured grain boundaries are more active, and hence low conductivity value is observed. The high conductive nature of grains become highly active at higher frequencies, thereby increasing the hopping of charge carrier between the ions, and conductivity is also increased at high frequencies [56,57]. When the concentration of Zn increases, the value of conductivity gradually decreases, and the Mn0 · 2Zn0 · 8Fe2O4 sample has the lowest value of conductivity among all the samples.

Fig. 16

Variation of the real part of ac conductivity with the frequency of Mn1-xZnxFe2O4 at 303 K.

The ac electrical conductivity of Mn1-xZnxFe2O4 ferrites at various temperatures are measured and shown in Fig. 17 . Conductivity increases with the temperature, which shows the semiconducting behavior of the samples. The temperature-dependent reciprocal ac conductivity is shown in Fig. 18 , and conductivity reveals the Arrhenius-type temperature dependence. The activation energy for the electrical conduction process is calculated from the least square straight-line fit, and the observed values are depicted in Table 3 . The values of activation energy show a strong dependence on Zn concentration. The calculated values of activation energy (0.43eV−0.62 eV) confirm that the electron hopping is main responsible for the process of electrical conduction in the samples [58]. Mn0.2Zn0.8Fe2O4 sample has the highest value of activation energy because of its low conductivity.

Fig. 17

Frequency-dependent variation of the real part of the ac conductivity of Mn1-xZnxFe2O4 measured at different temperatures.

Fig. 18

Arrhenius plots for the electrical conductivity of nanocrystalline Mn1-xZnxFe2O4.

Table 3

Activation energy (Ea) at 1 Hz, grain resistance (Rg), grain boundary resistance (Rgb), grain constant phase element (CPEg), grain constant phase element exponent (ng), grain boundary constant phase element (CPEgb), grain boundary constant phase element exponent (ngb), grain activation energy (Ea (g)) and grain boundary activation energy (Ea (gb)) of nanocrystalline Mn1-xZnxFe2O4 at 303 K.

X	Ea(eV)	Rg(Ω)	Rgb(Ω)	CPEg(F)	ng	CPEgb(F)	ngb	Ea(g)	Ea(gb)
								(eV)	(eV)
0.0	0.43	4.69 × 104	2.51 × 106	3.62 × 10−11	0.83	6.46 × 10−11	0.93	0.42	0.45
0.2	0.48	8.44 × 105	1.09 × 107	1.57 × 10−10	0.76	2.05 × 10−11	0.99	0.46	0.48
0.4	0.53	1.43 × 107	1.09 × 108	2.69 × 10−10	0.68	3.05 × 10−11	0.97	0.53	0.54
0.6	0.55	4.13 × 107	1.21 × 108	6.72 × 10−11	0.77	3.56 × 10−11	0.96	0.53	0.57
0.8	0.62	4.42 × 108	4.37 × 109	4.63 × 10−11	0.80	2.51 × 10−11	0.94	0.59	0.63
1.0	0.50	–	1.11 × 109	–	–	5.34 × 10−11	0.86	–	0.5

Impedance

The Cole–Cole plots of Mn1-xZnxFe2O4 ferrites are shown in Fig. 19 . The plot shows two overlapped depressed semicircles that characterize the grain boundary and grain contribution of the samples [59]. The Cole–Cole plots were modeled using (RgCPEg) (RgbCPEgb) equivalent circuit model and the values are obtained by fitting Cole–Cole plots for the proposed circuit at 303 K and presented in Table 3. Rgb values are higher than those of Rg values, whereas the CPEg values are higher than those of CPEgb values. This analysis shows that the contribution of grain boundary is higher compared with the grain to the resistance. Furthermore, the values of grain boundary and grain resistance increase with Zn, and the sample Mn0 · 2Zn0 · 8Fe2O4 has the highest resistance value because of its low conductivity. The Cole–Cole plot of the nanocrystalline Mn1-xZnxFe2O4 ferrites are measured at different temperatures and shown in Fig. 20 . The radius of the semicircle decreases with the increase in temperature because of the increment in electrical conductivity. The values of Rg and Rgb are obtained by fitting the plot to the proposed model. The values are plotted and shown in Fig. 21 . The Rg and Rgb values increase with Zn substitution. The activation energy calculated using the Arrhenius relation for the grain and grain boundary resistance, and given in Table 3. Among all samples, the x = 0.8 composition has the highest value of activation energy because of its high resistance.

Fig. 19

Cole-Cole plots of nanocrystalline Mn1-xZnxFe2O4 at 303 K.

Fig. 20

Cole-Cole plots of nanocrystalline Mn1-xZnxFe2O4 measured at different temperatures.

Fig. 21

Grain resistance (a) and grain boundary resistance (b) of nanocrystalline Mn1-xZnxFe2O4 at different temperatures.

Conclusion

The nanocrystalline Mn1-xZnxFe2O4 mixed ferrites were successfully synthesized using the combustion reaction method. All samples are single-phase and no extra phase was observed for Zn substitution. Studies on surface morphology analysis indicate that the synthesized ferrites are nano size and spherical shaped. Further, the SAED patterns point out the polycrystalline nature of the prepared ferrites. The X-ray photoelectron spectra show the presence of atoms Mn, Zn, Fe, and O in the Mn 2p, Zn 2p, Fe 2p, and O 1s states. The values of dielectric constant, tan δ, and ac electrical conductivity gradually decreases with Zn substitution up to x = 0.8. The activation energy of the nano ferrites increases from 0.44 eV (x = 0.0) to 0.62 eV (x = 0.8). The impedance study shows that the role of the grain boundary is predominant for electrical resistance, and the highest values of grain (4.42 × 108Ω) and grain boundary (4.37 × 109Ω) resistance are observed in the nanocrystalline Mn0 · 2Zn0 · 8Fe2O4 sample. The obtained results in the present investigation suggest that the prepared Zn substituted MnFe2O4 ferrite Mn0 · 2Zn0 · 8Fe2O4 nanoparticles are useful candidate material for high-frequency electronic device applications.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.