Microwave-assisted combustion synthesis of pure and zinc-doped copper ferrite nanoparticles: Structural, morphological, optical, vibrational, and magnetic behavior

Journal Pre-proof Microwave-assisted combustion synthesis of pure and zinc-doped copper ferrite nanoparticles: Structural, morphological, optical, vibrational, and magnetic behavior A. Tony Dhiwahar, M. Sundararajan, P. Sakthivel, Chandra Sekhar Dash, S. Yuvaraj PII:

S0022-3697(19)31884-0

DOI:

https://doi.org/10.1016/j.jpcs.2019.109257

Reference:

PCS 109257

To appear in:

Journal of Physics and Chemistry of Solids

Received Date: 24 July 2019 Revised Date:

1 November 2019

Accepted Date: 2 November 2019

Please cite this article as: A. Tony Dhiwahar, M. Sundararajan, P. Sakthivel, C.S. Dash, S. Yuvaraj, Microwave-assisted combustion synthesis of pure and zinc-doped copper ferrite nanoparticles: Structural, morphological, optical, vibrational, and magnetic behavior, Journal of Physics and Chemistry of Solids (2019), doi: https://doi.org/10.1016/j.jpcs.2019.109257. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier Ltd.

Graphical Abstract

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XCF1 XCZF2 XCZF3 XCZF4 XCZF5 XCZF6

Magnetization (emu/g)

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20

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-20

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-60 -15000

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Microwave-assisted combustion synthesis of pure and zinc-doped copper ferrite nanoparticles: structural, morphological, optical, vibrational, and magnetic behavior A. Tony Dhiwahara,c*, M. Sundararajanb,*,P.Sakthivelc, Chandra Sekhar Dashd, S. Yuvaraje

a

Department of Physics, Nehru Arts and Science College, Coimbatore, Tamil Nadu, 641105,

India b

PG and Research Department of Physics, Paavendhar College of Arts & Science, M.V. South,

Attur, Salem, Tamil Nadu, 636121, India c

PG & Research Department of Physics Urumu Dhanalakshmi College, Tiruchirappalli, Tamil

Nadu, 620020, India d

Department of Electronics and Communication Engineering, Centurion University of

Technology and Management, Bhubaneswar, Odisha,752050, India e

Department of Physics, Paavai Engineering College, Namakkal, Tamil Nadu,637408, India

*Corresponding author: Mobile no: +91-9047725916& +91-6374792232 E-mail: [email protected] & [email protected]

Abstract A microwave combustion method was used to synthesize Cu1-xZnxFe2O4 (x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) nanoparticles. The synthesized Zn-doped CuFe2O4 nanoparticles were characterized by techniques such as X-ray diffraction, high-resolution scanning electron microscopy, UVvisible diffuse reflectance spectroscopy, photoluminescence spectroscopy, Fourier transform IR spectroscopy, and vibrating-sample magnetometry. X-ray diffraction and Fourier transform IR spectroscopy results confirmed the formation of Cu1-xZnxFe2O4(x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) nanoparticles. The crystallite size and lattice parameter were determined as 15–19 nm and 8.319–8.400 Å, respectively. High-resolution scanning electron microscopy revealed the presence of agglomerated spherical particles of Cu1-xZnxFe2O4. Elemental mapping of pure and Zn-doped CuFe2O4 was done by energy-dispersive X-ray analysis. The band gap was calculated with the Kubelka-Munk function and was found to lie in the range from 2.30 to 2.51 eV. Finally,

1

M-H curves were plotted and the magnetic properties, such as coercivity, remanent magnetization, and saturation magnetization, were determined.

Keywords: Copper ferrite; Structural analysis; Morphological analysis; Vibrational analysis; Ferromagnetic materials

1. Introduction Recently, nanoferrites have been widely studied and used in various magnetic material applications, such as ferrofluid technology, magnetic resonance imaging, magnetocaloric refrigeration, high-density information storage systems, medical diagnostics, and gas sensors [1– 17]. The general chemical formula for the spinel ferrite structure is MFe2O4, where M= Co, Mg, Mn, Cu, Zn, Ni, etc. The spinel ferrite is formed by the distribution of cations that occupy tetrahedral (A) and octahedral (B) sites [18–20]. In general, the cation occupancy site is determined by factors such as the ionic radius, electronic configuration, crystal field, and ionic polarization [21]. Copper ferrite (CuFe2O4) possesses an inverse spinel structure, where Cu2+ions occupy the B site and Fe3+ and Cu2+ions occupy A and B sites [22–26]. Spinel-structured ferrite nanoparticles have been synthesized by various chemical techniques by mixing all the reagents at the molecular or atomic level. The most popular methods for the synthesis of ferrites are coprecipitation [27], sol-gel auto combustion [28], the standard ceramic method [29], the hydrothermal method [30], and combustion and microwave combustion [31, 32]. Wet-chemical methods [33] suffer from lower product yield and complex schedules. When compared with the aforementioned methods, the microwave combustion technique is attractive because of the interaction of the material with microwaves, which generates heat within the sample [34]. This energy assists in heating the sample at the molecular orbital level. During the reaction, molecular dipoles are induced and are caused to oscillate by microwaves. This oscillation enhances the rate of molecular collisions, thereby producing a huge amount of heat. Furthermore, this technique causes early phase formation and gives a fine particle size [35–42] as the heating is achieved within a few minutes. Thus it is feasible to control the reaction kinetics and thermodynamic aspects of the chemical reaction through microwaves in the combustion technique [43]. It further

2

offers certain advantages, such as low cost, higher yield, homogeneous chemical composition, and reaction products with higher purity [44, 45]. It was reported that pure zinc ferrite is an extraordinary semiconducting photocatalyst as it exhibits good photochemical stability in the visible region [46]. By doping with zinc ions, the composition of the host material can be modified, and this leads to improvement of structural, electrical, optical, and magnetic properties. Although zinc atoms are considered to be nonmagnetic, incorporation of zinc ions alters the entire structure (i.e., from normal to inverted spinel) and enhances the magnetic behavior. In particular, Zn2+-doped metal ferrites are used in various device applications, such as spintronic devices, massive storage devices, and gas-sensing devices [47]. Cu-Zn spinel ferrites possess excellent magnetic behavior that depends on the concentration of Zn2+ ions in CuFe2O4. The large saturation magnetization (Ms), high initial permeability, and high resistivity of Cu-Zn ferrites make them a prominent material for various applications, such as transformers, microwave latching devices, electrical switches, memory devices, inductors, and antenna cores[48,49]. In this work we report the preparation of Cu1-xZnxFe2O4 (x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) nanoparticles using the microwave combustion method and L-arginine as a fuel. The prepared nanoparticles were characterized by techniques such as X-ray diffraction (XRD), high-resolution scanning electron microscopy, energy-dispersive X-ray (EDX) spectroscopy, UV-visible diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy, Fourier transform IR (FT-IR) spectroscopy, and vibrating-sample magnetometry.

2. Experimental 2.1. Materials and methods All the chemicals used were of analytical grade and were obtained from Merck, India, and were used as obtained without further purification. Copper nitrate (Cu(NO3)23H2O; 98%), ferric nitrate (Fe(NO3)39H2O; 98%), and zinc nitrate (Zn(NO3)26H2O; 98%) were used precursor materials to synthesize Zn-doped CuFe2O4 nanoparticles, and L-arginine (C6H14N4O2; 98%) was used as a fuel. Zn-doped CuFe2O4 nanoparticles were prepared by incorporation of Zn2+ions in CuFe2O4invarious molar ratios to give Cu1-xZnxFe2O4(x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.5).

3

Precursor materials were mixed with L-arginine and transferred to a silica crucible, which was placed inside a microwave oven. Different kinds of compounds that contain nitrogen are used as fuels and reducing agents. High exothermicity of the reaction provides the self-propagating nature of the combustion process. In particular conditions, the temperature attained is very high within the reactant, which aids the formation. Metal ions and L-arginine are connected by intermolecular hydrogen bonds, leading to homogeneity [76, 77]. L-Arginine is used as an effective fuel as it assists in the phase formation of pure and Zn-doped CuFe2O4 of various compositions when calcination is performed at 500 °C. It helps in obtaining crystalline copper ferrite and Zn-doped copper ferrite nanoparticles [56]. The samples were irradiated with microwaves. Initially, the output power of the microwave oven was set at 800W for 15 min and the frequency was set at 2.54 GHz. On completion of the reaction, the solid powder obtained was cleaned with ethanol and deionized water and then calcined at 500 °C for 2 h. The stoichiometric reactions involved in the formation of pure and zinc-doped copper ferrite samples during the microwave combustion process using L-arginine as a fuel are as follows: 17Cu(NO3)2 3H2O(s) + 34Fe(NO3)3 9H2O(s) + 20C6H14N4O2(s)→ 17CuFe2O4(s) + 497H2O(g)↑ + 120CO2 (g)↑+ 108N2 (g)↑

(1)

17Cu(NO3)23H2O(s) + 17Zn(NO3)2 6H2O(s) + 34Fe(NO3)3 9H2O(s) + 26C6H14N4O2(s)→ 17CuZnFe2O4(s) + 641H2O(g)↑ + 156CO2(g)↑+ 137N2(g)↑

(2)

2.2. Characterization The phase composition and crystalline structure of as-prepared pure and Zn-doped CuFe2O4 were determined with a Rigaku Ultima IV high-resolution X-ray diffractometer with CuKα radiation at λ =0.15418 nm. The lattice parameters and crystallite size of the prepared ferrite samples were deduced from XRD data. Morphological and elemental analyses were performed with a JEOL JSM6360 high-resolution scanning electron microscope equipped with EDX analysis capability to determine the elements. The band gaps of the ferrite samples were estimated from the UV4

visible diffuse reflectance spectra; the DRS data were recorded with a Thermo Scientific Evolution 220UV-visible spectrophotometer. We used a Varian Cary Eclipse fluorescence spectrophotometer to record photoluminescence properties. The FT-IR spectra were recorded with a PerkinElmer Spectrum RX1spectrophotometer. Magnetic measurements were performed at room temperature with a PMC MicroMag 3900 vibrating-sample magnetometer equipped with a 1 T magnet.

3. Results and discussion 3.1. XRD analysis XRD patterns (see Fig.1) were studied to determine the crystal structure and phase purity of the synthesized Cu1-xZnxFe2O4 (x = 0.1, 0.2, 0.3, 0.4, and 0.5) nanoparticles. The observed reflection planes (220), (311), (400), (422), (511), (440), and (533) correspond to diffraction angles of 30.32°, 35.76°,43.04°, 53.76°, 57.51°, 62.80°, and 74.19°, respectively. The observed diffraction peaks matched perfectly with JCPDS card number 77-0010 for standard CuFe2O4. The XRD pattern of Zn2+-doped CuFe2O4 confirmed the formation of a single-phase cubic spinel structure with space group Fd m [50]. On comparing the diffraction peak at 2θ = 35.76° of pure CuFe2O4 with that of Zn-doped CuFe2O4 samples, we observed a slight shift in the diffraction peak to lower diffraction angle. This peak shift is attributed to the incorporation of Zn2+ ions into the host lattice of CuFe2O4. As shown in Fig.2, with increase in Zn dopant composition, the peak approached the strong diffraction peak of undoped CuFe2O4.The average crystallite size L was deduced for various Zn-substituted CuFe2O4 samples with use of the Debye-Scherrer equation:

L=

kλ , β cosθ

(3)

where L is the crystalline size, λ is the X-ray wavelength (0.15418 nm), β is the full width at half maximum, and 2θ is the diffraction angle. The concentration of the Zn2+ ion in copper ferrite affects the strength of the crystalline phase. In this case, the crystalline phase of CuFe2O4is considered as the most incomplete and of the lowest strength, whereas the Cu0.7Zn0.3Fe2O4 crystal phase is the most complete and has the highest strength. Because of the change in the crystalline phase, the peak intensity decreases for x = 0.4 and then increases for x = 0.5 [51]. As indicated in the XRD patterns, the linear change in

5

peak width was reflected in a linear decrease in crystallite size from 19.37 to 15.21 nm with increase in Zn content in the host sublattice of CuFe2O4, as shown in Table 1. This eventually leads to a decrease of the particle size. From the XRD patterns, the most intense peak is found to correspond to the (311) reflection plane. The lattice constants of the pure and Zn-doped copper ferrite nanoparticles were calculated from the respective (hkl) and dspacing parameters with use of Eq. (4), (4)

a = d hkl (h 2 + k 2 + l 2 ) where h, k, and l are Miller indices of the crystal planes and d is the interplanar distance. Lattice constants were determined for every sample individually and are summarized in Table 1. An increase in the lattice constant from 8.319 to 8.400 Å is observed with increase in Zn2+ ion content in the host sublattice of CuFe2O4, thus obeying Vegard’s law [27]. This increase in the lattice constant is governed by following factors: (i) the increased ionic radius, as the doping cation Zn2+ (0.74Å) has a bigger ionic radius than Cu2+(0.73Å); (ii) probable redistribution of Cu2+ ions within the tetrahedral/octahedral ionic site, which is responsible for tuning the magnetic properties [27, 52–55]. The effective particle size (D) is deduced with use of the Williamson-Hall equation Eq. (5), (5)

β cos θ k 4ε sin θ = + λ D λ

where β is the full width at half maximum of the XRD peak, θ is the diffraction angle, k is a constant equal to 0.89, λ is the wavelength of the X-ray source (λ = 0.15418 nm), and ε is the strain associated with the nanoparticles. Strain (ε) is determined with Eq. (5) by a WilliamsonHall plot of 4sin θ/λ versus βcos θ/λ, and the effective particle size (D) is determined from the intercept (k/D). Williamson-Hall plots of copper ferrite and zinc-doped copper ferrite samples are shown Fig. 3.The effective particle size determined by the Williamson-Hall method was lower than the average crystallite size obtained with the Debye-Scherer formula, which may be due to the strain components in the Williamson-Hall method. From Table 1, it is obvious that the crystallite size decreases with increasing Zn2+ content (x), while the lattice constant increases.

6

3.2. High-resolution scanning electron microscopy analysis High-resolution scanning electron microscopy was performed to study the morphology of Cu1xZnxFe2O4(x=0.0,

0.1, 0.2, 0.3, 0.4, and 0.5) nanoparticles; images are shown in Fig. 4.On visual

inspection, Cu1-xZnxFe2O4 samples revealed a compact arrangement of spherical well-defined crystallite grains. Fig. 4(a) shows an image of undoped CuFe2O4nanoparticles and Fig. 4(b)–(f) shows images of Zn-doped Cu ferrite nanoparticles, which were found to be homogeneous and agglomerated. The agglomerates are observed because of the interaction between molecules. It is highly likely that agglomerates formed during the microwave irradiation phase of the microwave combustion method. Homogeneous spherical nanoparticles were obtained as a result of calcination of the nanoparticles at 500 °C. Such homogeneous spherical nanoparticles were also observed by Sundararajan et al. [56, 57] in Mg-doped cobalt ferrite spinel nanoparticles and Cosubstituted zinc ferrite nanoparticles.

3.3. EDX analysis EDX spectra of pure and Zn-doped copper ferrite are depicted in Fig.5. The presence of Fe, Cu, and O peaks indicates the formation of undoped CuFe2O4 (see Fig. 5(a)). Fig. 5(b)–(f) shows the EDX spectra of Zn-doped CuFe2O4 samples. The percentages of Zn and Cu obtained match well with the amount of Zn and Cu desired in the as-prepared stoichiometric CuFe2O4 and Zn-doped CuFe2O4samples. The experimental conditions completely favor the formation of mixed ferrite. The results confirm the impurity formation of CuFe2O4 and Zn-doped CuFe2O4. 3.4. UV-visible DRS analysis UV-visible DRS measurements were used to determine the band gap of the Cu1-xZnxFe2O4(x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) nanoparticles. The Tauc relation was used to determine the band gap. In general, the Kubelka-Munk function was applied with Eq. (6) to convert the diffuse reflectance into the absorption coefficient:

α = F ( R) =

(1 − R ) 2 , 2R

(6)

7

where α denotes to absorption coefficient, F(R) is the Kubelka-Munk function, and R is reflectance. The Tauc relation is given by Eq. (7): F(R)hν= A(hν−Eg)n,

(7)

where n = 2 denotes a direct transition, which corresponds to a direct band gap, while n=1/2 denotes an indirect transition and corresponds to an indirect band gap [58].(F(R)hʋ)2 was plotted versus the band gap (hʋ), and the intercept obtained is the band gap (Fig. 6). The estimated band gaps of Cu1-xZnxFe2O4(x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) nanoparticles are2.30, 2.35, 2.38, 2.40, 2.43, and 2.51 eV, respectively (Fig. 7). The band gap of pure copper ferrite was observed to be lower than that of the bulk CuFe2O4 nanoparticles (3.35 eV) [27]. An increase in the optical band gap and a decrease in crystallite size is clearly seen, which is mainly attributed to the quantum confinement effect. The same effect was observed by Hammad et al. [27], Wang et al. [59], and Chen et al. [60]. In general, different parameters, such as impurities, carrier concentrations, crystallite size, and lattice strain, may influence and cause an increase in the optical band gap when Zn2+ ions are incorporated into copper ferrites. In this case, the increase in the optical band gap is due to the sp-d exchange interaction between the band electrons of copper ferrites and localized d electrons of divalent zinc ions [61–65].

3.5. Photoluminescence analysis To investigate on the phenomenon of recombination and the relative energy position of subband-gap defect states, photoluminescence spectra were recorded [66]. Fig.8 depicts the photoluminescence spectra of Cu1-xZnxFe2O4 nanoparticles recorded at room temperature with an excitation wavelength of 385 nm. Because of the recombination of excited electrons and holes, peaks were observed in the range from 415 to 437 nm. Violet emission was seen in the visible region between 400 and 450 nm because of the presence of oxygen vacancies and grain boundaries in Cu1-xZnxFe2O4 nanoparticles [67]. As a result of incorporation of Zn into the matrix of CuFe2O4, an increase in the luminescence intensity was observed with increase in the value of x upto 0.4, but a sudden decrease in luminescence intensity was seen with increase in Zn concentration (x=0.5). This indicates saturation of Zn concentration in the tetrahedral (A) site. Although utmost care was taken while preparing the samples, the increase in the luminescence intensity is attributed to the increase in the distance between the dopant (activator) and the array [68]. Furthermore, the presence of defect centers, which serve as trap levels, and the presence of 8

Zn2+ activators are responsible for the increase in the luminescence intensity in Zn-doped copper ferrites [69].

3.6. FT-IR analysis The FT-IR spectra of copper ferrite and zinc-doped copper ferrite spinels were recorded in the range between 4000 and 400cm-1at room temperature, as shown in Fig. 9.A broad band around 3480 cm-1 is observed, which is assigned to the stretching vibrations of O–H groups of the water molecule [70].The peaks at 2357 and 1615 cm-1are assigned to H–O–H bending vibration of the free or absorbed water [71]. Furthermore, during the preparation of the nanoparticles, some water was retained in them, which is confirmed by the occurrence of bands at1115cm-1[70]. The main band, located at 883 cm-1, confirms the formation of the spinel phase and is assigned to vibration of Cu–O [72]. Because of the effect of intrinsic stretching vibrations of the tetrahedral sites of Fe3+–O2−, a band at 575 cm-1 is observed. Furthermore, a band was observed in the range from800 to 400cm-1, which is associated with the stretching vibrations of the metal at, tetrahedral (A) sites, Mtetra↔O. Finally, a band in the range from 470 to 477 cm-1was found and is associated with the metal stretching of Cu cations at octahedral (B) sites [73].

3.7. Magnetization analysis The magnetic characteristics of the Cu1-xZnxFe2O4(x=0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) nanoparticles were studied with a vibrating-sample magnetometer and variation of the applied magnetic field in the range from -15 to +15kOe at room temperature. The magnetic characteristics of the crystalline materials are dependent on factors such as the distribution of the cations in the tetrahedral (A) and octahedral (B) sites and the chemical composition of the synthesized nanoparticles [68].The synthesized samples exhibited ferromagnetic behavior; the hysteresis loops obtained for nanocrystalline Cu1-xZnxFe2O4 samples are illustrated in Fig.10. Xiao et al. [74] and Jiang et al. [75] also observed ferromagnetic (S-shaped loop) behavior. The magnetic parameters are summarized in Table 2. We recorded the highest value of Ms (54.46 emu/g) for x=0.4; it dropped to a minimum value of 17.37 emu/g with decrease in Zn content (i.e., x=0). Similarly, coercivity (Hc) increased with increase in Zn content (Fig. 11) and had a 9

maximum value of 162.95 emu/g for x=0.4 and dropped to a lower value of 63.79 emu/g for x = 0.3.The magnetic and structural behavior of nanocrystalline Cu-Zn ferrites is highly related to the cation distribution and chemical composition. Upto x = 0.3, some nonmagnetic Zn2+ ions migrate into the B site from the A site and cause a decrease in Hc. For x = 0.4, Hc increases because of the modification of the magnetic ion distribution where nonmagnetic Zn2+ ions occupy the tetrahedral (A) site and Fe3+ ions occupy both the tetrahedral (A) site and the octahedral (B) site. Hence the net magnetization of Cu-Zn ferrite depends solely on the occupation sites of nonmagnetic Zn2+ ions in copper ferrites. We recorded maximum remanent magnetization (Mr) of 13.02 emu/g for x= 0.4 and a minimum value of 5.21 emu/g for x= 0 due to cation redistribution in the nanoregime at octahedral and tetrahedral sites, lattice defects, and magnetic super exchange interaction between tetrahedral and octahedral sites [62, 64]. This magnetic interaction results in a compositional variation and is caused by the distribution of cations in the octahedral and tetrahedral sites. The structural and magnetic properties of Zn-Cu ferrite nanoparticles are strongly influenced by the percentage of Zn doping.

4. Conclusions

Cu1-xZnxFe2O4 (x = 0.1, 0.2, 0.3, 0.4, and 0.5) nanoparticles were successfully synthesized by a microwave-assisted combustion method. X-ray analysis revealed the formation of a single-phase cubic spinel structure. The lattice parameter increased from 8.319 to 8.400 Å with increase in Zn2+ concentration. The band gap of the pure CuFe2O4 nanoparticles was found to be 2.30 eV. A quantum confinement effect was confirmed as the band gap increased from 2.30 to 2.51 eV and the crystallite size decreased. Ms and Mr increased with the increase in Zn2+concentration in copper

ferrites

upto

x=0.4

and

subsequently decreased

with

further

increase

of

Zn2+concentration. The decrease in magnetization for x = 0.5is due to the change in the cation distribution at tetrahedral and octahedral sites. It also confirmed that Cu1-xZnxFe2O4 nanoparticles exhibited a soft magnetic nature.

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[77] R. Ianos, I. Lazau, C. Pacurariu, P. Barvinschi, Application of new organic fuels in the direct MgAl2O4combustion synthesis, Eur. J. Inorg. Chem. 2008(6) (2018) 931-938. Figure Captions Fig. 1.X-ray diffraction patterns of Cu1-xZnxFe2O4nanoparticles. Fig. 2.Peak-shift position of (311) diffraction planes in Cu1-xZnxFe2O4 nanoparticles. Fig. 3.Williamson-Hall patterns of Cu1-xZnxFe2O4nanoparticles.XCF1, CuFe2O4; XCZF2,

Cu0.9Zn0.1Fe2O4; XCZF3, Cu0.8Zn0.2Fe2O4; XCZF4, Cu0.7Zn0.3Fe2O4; XCZF5, Cu0.6Zn0.4Fe2O4; XCZF6, Cu0.5Zn0.5Fe2O4. Fig. 4.High-resolution scanning electron microscopy images of (a) CuFe2O4, (b) Cu0.9Zn0.1Fe2O4,

(c) Cu0.8Zn0.2Fe2O4, (d) Cu0.7Zn0.3Fe2O4, (e) Cu0.6Zn0.4Fe2O4, and (f) Cu0.5Zn0.5Fe2O4. Fig.5.Energy-dispersive X-ray spectra of (a) CuFe2O4, (b) Cu0.9Zn0.1Fe2O4, (c) Cu0.8Zn0.2Fe2O4,

(d) Cu0.7Zn0.3Fe2O4, (e) Cu0.6Zn0.4Fe2O4, and (f) Cu0.5Zn0.5Fe2O4. Fig. 6.(F(R)hʋ)2 versus hʋ for Cu1-xZnxFe2O4nanoparticles.XCF1, CuFe2O4; XCZF2,

Cu0.9Zn0.1Fe2O4; XCZF3, Cu0.8Zn0.2Fe2O4; XCZF4, Cu0.7Zn0.3Fe2O4; XCZF5, Cu0.6Zn0.4Fe2O4; XCZF6, Cu0.5Zn0.5Fe2O4. Fig. 7.Band gap versus Zn2+ fraction of Cu1-xZnxFe2O4nanoparticles. Fig.8. Photoluminescence (PL) spectra of Cu1-xZnxFe2O4nanoparticles.XCF1, CuFe2O4; XCZF2,

Cu0.9Zn0.1Fe2O4; XCZF3, Cu0.8Zn0.2Fe2O4; XCZF4, Cu0.7Zn0.3Fe2O4; XCZF5, Cu0.6Zn0.4Fe2O4; XCZF6, Cu0.5Zn0.5Fe2O4. Fig. 9. FT-IR spectra of Cu1-xZnxFe2O4 for (a) x =0 (b) x = 0.1(c) x = 0.2 (d) x = 0.3 (e) x = 0.4and (f) x = 0.5 nanoparticles. Fig. 10.Hysteresis loop of Cu1-xZnxFe2O4nanoparticles.XCF1, CuFe2O4; XCZF2,

Cu0.9Zn0.1Fe2O4; XCZF3, Cu0.8Zn0.2Fe2O4; XCZF4, Cu0.7Zn0.3Fe2O4; XCZF5, Cu0.6Zn0.4Fe2O4; XCZF6, Cu0.5Zn0.5Fe2O4. Fig. 11. Variation of (a) coercivity, (b) Remanent magnetization, and (c) saturation

magnetization of Cu1-xZnxFe2O4nanoparticles. 18

Table Captions Table 1.Crystallite size, lattice parameter, and energy gap of Cu1-xZnxFe2O4nanoparticles. Table 2.Coercivity, remanent magnetization, and saturation magnetization of Cu1-xZnxFe2O4

nanoparticles. Table 1

Sample

Crystallite

Effective

Lattice

Energy gap

size, L (nm)

crystallite

parameter, a

Eg, (eV)

size, D (nm),

(Å)

by WilliamHall plot CuFe2O4

19.37

19.24

8.319

2.30

Cu0.9Zn0.1Fe2O4

19.25

18.75

8.323

2.35

Cu0.8Zn0.2Fe2O4

18.51

17.25

8.328

2.38

Cu0.7Zn0.3Fe2O4

17.14

16.35

8.331

2.40

Cu0.6Zn0.4Fe2O4

16.67

14.55

8.337

2.43

Cu0.5Zn0.5Fe2O4

15.21

13.15

8.400

2.51

19

Table 2

Sample

Hc(Oe)

Mr(emu/g)

CuFe2O4

337.01

5.21

17.37

Cu0.9Zn0.1Fe2O4

109.48

6.37

33.31

Cu0.8Zn0.2Fe2O4

81.32

8.96

44.10

Cu0.7Zn0.3Fe2O4

63.79

10.48

52.49

Cu0.6Zn0.4Fe2O4

162.95

13.02

54.46

Cu0.5Zn0.5Fe2O4

97.29

9.41

49.91

20

Ms (emu/g)

533

440

511

422

400

220

311

x=0.5

Intensity (a.u)

x=0.4

x=0.3

x=0.2 x=0.1 x=0

20

30

40

50

60

70

80

2θ (degree)

Fig. 1. XRD patterns of Cu1-xZnxFe2O4 (0 ≤ x ≤ 0.5) nanoparticles.

26

2θ=35.655

(311) x=0.5

Intensity (a.u)

x=0.4

x=0.3 x=0.2

2θ=35.801

x=0.1 x=0

35.1

35.2

35.3

35.4

35.5

35.6

35.7

35.8

35.9

36.0

36.1

36.2

2 Theta (deg)

Fig. 2. The peak-shift position of (311) diffraction planes in Cu1-xZnxFe2O4 (0 ≤ x ≤ 0.5) nanoparticles.

27

β cosθ/λ

0.2

0.1

XCF1 XCZF2 XCZF3 XCZF4 XCZF5 XCZF6

0.0

-0.1 0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

4sinθ/λ

Fig. 3. W-H patterns of Cu1-xZnxFe2O4 (0 ≤ x ≤ 0.5) nanoparticles.

28

(b)

(a)

(f)

(d)

(c)

(f)

(e)

s1 s1

Fig. 4. HR-SEM images of (a) XCF1, (b) XCZF2, (c) XCZF3, (d) XCZF4, (e) XCZF5 and (f) XCZF6 samples.

29

(b)

(a)

(c)

(d)

(e)

(f)

Fig.5. EDX spectra of (a) XCF1, (b) XCZF2, (c) XCZF3, (d) XCZF4, (e) XCZF5 and (f) XCZF6 samples.

30

XCF1

1200

XCZF2

1400 1200

1000

1000 800

800 600

600 400

400 200

200 0

0 1.5

2.0

2.5

3.0

3.5

1.5

4.0

2.5

3.0

3.5

4.0

2.0

2.5

3.0

3.5

4.0

XCZF4

1400

XCZF3

1400

2.0

1200 1200

(F(R)hʋ)2

1000 1000 800 800 600 600 400 400 200 200 0 0

1.5 1.5

2.0

2.5

3.0

3.5

4.0 1600

1500

XCZF5

XCZF6

1400 1200

1200 1000

900 800 600

600 400

300 200 0 1.5

2.0

2.5

3.0

3.5

2.0

4.0

2.5

hʋ (eV)

Fig. 6. (F(R)hʋ)2 versus hʋ plot of Cu1-xZnxFe2O4 (0 ≤ x ≤ 0.5) nanoparticles.

31

3.0

3.5

4.0

2.50

Band gap (eV)

2.48

2.46

2.44

2.42

2.40

2.38 0.0

0.1

0.2

0.3

0.4

0.5

2+

Zn fraction

Fig. 7. Band gap versus Zn2+ fraction of Cu1-xZnxFe2O4 (0 ≤ x ≤ 0.5) nanoparticles.

32

XCF1 XCZF2 XCZF3 XCZF4 XCZF5 XCZF6

1200000

PL Intensity (a.u)

1000000

800000

600000

400000

200000

0 400

450

500

550

Wavelength (nm)

Fig. 8. Photoluminescence spectra of Cu1-xZnxFe2O4 (0 ≤ x ≤ 0.5) nanoparticles.

33

(f) (e)

Transmittance (%T)

(d) (c)

(b) (a)

3500

3000

2500

2000

1500

1000

-1

Wavenumber (cm )

Fig. 9. FT-IR spectra of Cu1-xZnxFe2O4 (0 ≤ x ≤ 0.5) nanoparticles.

34

500

60

XCF1 XCZF2 XCZF3 XCZF4 XCZF5 XCZF6

Magnetization (emu/g)

40

20

0

-20

-40

-60 -15000

-10000

-5000

0

5000

10000

15000

Applied field (Oe)

Fig. 10. Hysteresis loop of Cu1-xZnxFe2O4 (0 ≤ x ≤ 0.5) nanoparticles. .

35

14

a

300

Coercivity Hc(Oe)

b Remanant magnetization Mr(emu/g)

350

250

200

150

100

12

10

8

6

4

50 0.0

0.1

0.2

0.3

0.4

0.0

0.5

0.1

0.2

0.4

0.5

Zn fraction

c

55

Saturation magnetization Ms (emu/g)

0.3 2+

2+

Zn fraction

50 45 40 35 30 25 20 15 0.0

0.1

0.2

0.3

0.4

0.5

2+

Zn fraction

Fig. 11. Variation of (a) coercivity, (b) remanant magnetization and (c) saturation magnetization of Cu1-xZnxFe2O4 (0 ≤ x ≤ 0.5) nanoparticles.

36

Highlights •

Zinc-doped copper ferrite was synthesized by a microwave combustion method.

•

Structural, morphological, optical, vibrational, and magnetic properties are studied.

•

Zinc-doped copper ferrite nanoparticles exhibit ferromagnetic behavior.

1

Authors declare no conflict of Interest.