Microwave combustion synthesis of zinc substituted nanocrystalline spinel cobalt ferrite: Structural and magnetic studies

Microwave combustion synthesis of zinc substituted nanocrystalline spinel cobalt ferrite: Structural and magnetic studies

Materials Science in Semiconductor Processing 40 (2015) 1–10 Contents lists available at ScienceDirect Materials Science in Semiconductor Processing...

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Materials Science in Semiconductor Processing 40 (2015) 1–10

Contents lists available at ScienceDirect

Materials Science in Semiconductor Processing journal homepage: www.elsevier.com/locate/mssp

Microwave combustion synthesis of zinc substituted nanocrystalline spinel cobalt ferrite: Structural and magnetic studies M. Sundararajan a, L. John Kennedy a,n, Udaya Aruldoss b, Sk. Khadeer Pasha c, J. Judith Vijaya d, Steve Dunn e a

Materials Division, School of Advanced Sciences, Vellore Institute of Technology (VIT) University, Chennai Campus, Chennai 600127, India Department of Chemistry, College of Engineering Guindy, Anna University Chennai, Chennai 600025, Tamil Nadu, India c Materials Physics Division, School of Advanced Sciences, Vellore Institute of Technology (VIT) University, Vellore Campus, Vellore 632014, India d Catalysis and Nanomaterials Research Laboratory, Department of Chemistry, Loyola College, Chennai 600034, India e School of Engineering & Materials Science, Queen Mary, University of London, Mile End Road, London, United Kingdom b

a r t i c l e i n f o

Keywords: Ferrite nanoparticles Microwave processing Optical property Stretching frequencies Magnetic property

abstract Zinc doped cobalt ferrite spinel nanoparticles were prepared by the microwave combustion method. All the samples were characterized by using X-ray diffraction technique (XRD), Scanning Electron Microscopy, energy dispersive X-ray analysis, UV–visible diffuse reflectance spectroscopy, Fourier transformed infrared (FT-IR) spectroscopy and vibrating sample magnetometry. The XRD patterns confirmed the formation of single phase CoFe2O4 inverse spinel structure without impurities. The lattice parameter increased from 8.380 to 8.396 Å with increasing Zn2 þ fraction. The average crystallite sizes obtained by a Scherrer method varied between 46.22 nm and 30.79 nm. The estimated band gap energy values increases with an increasing zinc fraction (1.88–2.10 eV). The elemental composition of Zn, Co, and Fe was qualitatively obtained from energy dispersive X-ray (EDX) analysis. & 2015 Elsevier Ltd. All rights reserved.

1. Introduction Nanostructured materials that are finding wider applications are prepared using bottom-up approach in the past few years. The spinel ferrite structure MFe2O4, where M refers to the metal, can be described as a cubic close-packed arrangement of oxygen atoms, with M2 þ and Fe3 þ at two different crystallographic sites. These sites have tetrahedral and octahedral oxygen coordination termed as A and Bsites, respectively [1,2]. The spinel crystal structure has A2 þ cations at Wyckoff positions 8a (1/8, 1/8, 1/8), B3 þ cations at

n Corresponding author. Tel.: þ91 44 39931326; fax: þ91 44 39932555. E-mail address: [email protected] (L.J. Kennedy).

http://dx.doi.org/10.1016/j.mssp.2015.06.002 1369-8001/& 2015 Elsevier Ltd. All rights reserved.

16d (1/2, 1/2, 1/2), and oxygen at 32e (u, u, u), where the positional parameter of oxygen is conventionally called as u-parameter. There are three ideal structures namely normal, inverse and mixed spinel structures. Normal spinel structure, where all M2 þ ions occupy A-sites (tetrahedral site) and Fe3 þ ions occupy B-sites (octahedral site); struch i tural formula of such ferrites is M2 þ Fe32 þ O24  . Inverse spinel structure, where all M2 þ ions are in B-positions and Fe3 þ ions are equally distributed between A and B-sites, structural formula of these ferrites are Fe3 þ [M2 þ Fe3 þ ] O24  . Mixed spinel structure, when cations M2 þ and Fe3 þ occupy both A and B-positions; structural formula of this h i 2 3þ ferrite is M21 þ M2δ þ Fe32 þ  δ Feδ  δ O4 , where δ is the degree of inversion [3,4].

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Among the ferrites, cobalt ferrite (CoFe2O4) is a well known inverse spinel structure, because of its high coercivity, moderate saturation magnetization, large magnetocrystalline anisotropy, large magnetostrictive coefficient at room temperature [5]. The mechanical hardness, chemical stability, flexible magnetic properties makes these materials a promising one for magneto-optical recording, electronic devices, high density magnetic recording devices [6,7], supercapacitors, photo-magnetic devices, photocatalysis and hydrogen production [8–11]. Various preparation methods like microemulsions [12], solvo-thermal, hydrothermal approach [13], sol–gel method [14], combustion, laser deposition, thermal decomposition method [15], chemical co-precipitation technique etc., [16] are reported for the synthesis of cobalt ferrites. Among the various methods reported, microwave combustion technique is probably opted for homogeneity, high purity and improved characteristics. The microwave energy is an internal means of heat energy generation and conversion. The microwave energy is transformed into heat energy by strong intermolecular friction and rises the temperature of the precursor materials suddenly [17]. Fuels like urea, glycine, citric acid, Lalanine or carbohydrazide in an appropriate stoichiometric ratio controls the combustion process in accordance with the propellant chemistry principles [22]. As a result, the crystallite size, morphology, textural, surface area, and other physicochemical properties are largely altered. Also, the use of microwave energy as heating source, speeds up the chemical reaction and kinetics, improve the economical viability, and reduces the energy loss [18]. In the present work, we have synthesized zinc substituted cobalt ferrite nanoparticles by the microwave combustion method employing L-arginine as a fuel. L-arginine is found to facilitate the homogeneous mixing of cations in solution and it undergoes decomposition and promotes combustion. The literature on the preparation of zinc ferrite using L-arginine is found to be scarce. We have investigated the effect of this fuel to evaluate the characteristics like surface morphology, size distribution, and magnetic properties of pure and zinc substituted cobalt ferrite nanoparticles. The ferrites thus prepared were characterized by X-ray diffraction (XRD) for the structural analysis; scanning electron microscopy (HR-SEM) for surface morphology; energy dispersive X-ray (EDX) analysis for chemical composition; diffuse reflectance spectroscopy (DRS) for energy band gap estimation; and Fourier transform infrared (FT-IR) spectral studies for vibrational stretching frequencies. The magnetic behavior of the samples was studied using vibrating sample magnetometry (VSM).

2.2. Preparation of Zn doped CoFe2O4 spinels The mole percentage of Co1 xZnxFe2O4 with x fraction varying as 0, 0.1, 0.2, 0.3, 0.4, and 0.5 was prepared by dissolving stoichiometric quantities of precursors like zinc nitrate, cobalt nitrate, ferric nitrate and L-arginine in double distilled water. The precursor solution in a beaker was stirred for about 1 h at room temperature to obtain a clear homogeneous solution. L-arginine served as a fuel, while the nitrates in the precursors served as the oxidizers. The fuel to oxidizer ratio (F/O) was taken to be 1 as per the concept of propellant chemistry. The homogeneous reaction solution mixture after rigorous stirring were transferred into silica crucible and placed inside a microwave oven (SAMSUNG, India Limited) for irradiation. Microwave was irradiated over the precursor solution for 10 min at 900 W output power at 2.54 GHz frequency. Primarily, the solution boiled and underwent rigorous decomposition with gas evolution. When the solution reached the point of spontaneous combustion, ignition took place resulting in a rapid flame and yielding a solid fluffy final products of Co1  xZnxFe2O4 (x¼0–0.5). The samples CoFe2O4, Co0.9Zn0.1Fe2O4, Co0.8Zn0.2Fe2O4, Co0.7Zn0.3Fe2O4, Co0.6Zn0.4Fe2O4, Co0.5Zn0.5Fe2O4, were labeled as CoF1, CoZF2, CoZF3, CoZF4, CoZF5, and CoZF6 respectively. The chemical reaction involved in the formation of cobalt ferrite during the combustion process employing L-arginine is given in Eq. (1) CoðNO3 Þ2 6H2 OðSÞ þ 2FeðNO3 Þ3 9H2 OðSÞ þ1:176C6 H14 N4 O2ðSÞ -CoFe2 O4ðSÞ þ 32:23H2 OðgÞ ↑ þ7:05CO2ðgÞ ↑ þ 6:35N2ðgÞ ↑

ð1Þ

2.3. Characterization techniques The crystalline structure of the resultant nanoparticles was performed using Rigaku Ultima IV high resolution Xray powder diffractometer for 2θ values ranging from 101 to 801 using CuKα radiation at λ ¼1.5418 Å. The surface morphology of the samples were analyzed at a desired magnification with a Joel JSM 6360 high resolution scanning electron microscope (HR-SEM) equipped with energy dispersive X-ray (EDX) analyzer for elemental composition analysis. The diffuse reflectance spectrum (DRS) in the UV– visible range was recorded using Thermo scientific evolution 300 UV–visible spectrophotometer to estimate the optical band gap. The FT-IR spectrum was recorded on a Thermo scientific Nicolet iS10 infrared spectrophotometer. The vibrating sample magnetometry measurements were carried out using Lakeshore VSM 7410 model equipped with 3 T magnets at 300 K.

2. Experimental 3. Results and discussion 2.1. Materials 3.1. XRD analysis All the chemicals used in the present study, such as, zinc nitrate, cobalt nitrate, ferric nitrate and L-arginine were of analytical grade, purchased from Merck, India. The chemicals were used as received without further purification. Double distilled water was used during the sample preparation.

The crystal structure and phase purity of pure and Zn doped CoFe2O4 samples were confirmed from the X-ray diffraction patterns as shown in Fig. 1(a)–(f). The diffraction peaks at 2θ values of 18.271, 30.051, 35.431, 37.011, 43.021, 56.951 and 62.481 are indexed to (111), (220), (311),

M. Sundararajan et al. / Materials Science in Semiconductor Processing 40 (2015) 1–10

(222), (400), (511) and (440) reflections planes of cobalt ferrite respectively. All the peaks match well with the JCPDS card number, 22-1086 signifying the cubic spinel structure with Fd3m space group symmetry. There are no additional peaks attributing to the impurity phases in all the zinc substituted samples indicating the substitution of Zn in cobalt ferrite matrices. The average crystallite size was calculated according to the Scherrer equation (2) [19] L¼

0:89λ β cos θ

ð2Þ

was estimated using the relation (3). h

β ¼ β2 measured –β2 instrumental

i1=2

ð3Þ

The estimated crystallite size for pure and zinc doped cobalt ferrites are shown in Table 1. The crystallite size calculated for CoF1, CoZF2, CoZF3, CoZF4, CoZF5 and CoZF6 ferrites are found to be 46.22, 43.33, 41.31, 35.27, 32.58 and 30.79 nm respectively. The decrease in the crystallite size against increase in Zn2 þ ions concentration is due to the lower bond energy of Zn þ 2 –O  2 (159 kJ/mol) as compared to Co þ 2 –O  2 (384 kJ/mol) [20]. The lattice parameters of the ferrite spinels were calculated from the Xray diffraction patterns using Eq. (4) as follows [28]: 2

2

2

a ¼ dhkl ðh þk þl Þ1=2

ð4Þ

where ‘a’ is the lattice parameter; dhkl, the interplanar spacing corresponding to the miller indices; and h, k, and l are the miller indices of the crystal planes [21]. The calculated lattice parameters are shown in Table 1. It is inferred that the lattice parameter, ‘a’ for CoFe2O4 is in good agreement with the reported value (8.383 Å) by Tang

311

where β is the full width at half maximum (FWHM) of diffraction peak; λ, the X-ray wavelength (0.15418 nm); L, the crystallite size; and 2θ, the diffraction angle. The width of the Bragg peak is the combination of both instrument and sample broadening effects. Hence, the line broadening due to the instrument has to be decoupled with that of the sample by recording the diffraction pattern and studying the line broadening of a standard material such as aluminum oxide (corundum). The instrumental corrected broadening [19], β corresponding to the diffraction peak of cobalt ferrites

3

440

(f)

8.394

Lattice parameter a, (Å)

220

400

511

8.397

Intensity (a.u.)

(e) (d) (c)

(b)

8.391

8.388

8.385

8.382

(a) 8.379 10

20

30

40

50

60

70

80

0.0

0.1

0.2

0.3

0.4

0.5

Zinc fraction

θ (degree) Fig. 1. X-ray diffraction patterns of (a) CoF1, (b) CoZF2, (c) CoZF3, (d) CoZF4, (e) CoZF5 and (f) CoZF6 samples.

Fig. 2. Lattice parameter of Co1  xZnxFe2O4 (0 r xr 0.5) with zinc fraction.

Table 1 Sample code, crystallite size, lattice parameter, Rietveld refinement factors and band gap energy values of Co1  xZnxFe2O4 system. Sample

Sample code

Crystallite size, L (nm)

Lattice parameters, a (Å)

Fit parameters

Energy gap (eV)

CoFe2O4

CoF1

46.22

8.380

1.88

Co0.9Zn0.1Fe2O4 CoZF2

43.33

8.382

Co0.8Zn0.2Fe2O4 CoZF3 Co0.7Zn0.3Fe2O4 CoZF4

41.31 35.27

8.386 8.390

Co0.6Zn0.4Fe2O4 CoZF5

32.58

8.393

Co0.5Zn0.5Fe2O4 CoZF6

30.79

8.396

Rwp ¼5.72% Rp ¼ 4.46% Re ¼ 5.97% S ¼0.96 χ2 ¼ 0.92 Rwp ¼6.03% Rp ¼4.66% Re ¼6.42% S ¼0.94 χ2 ¼ 0.88 Rwp ¼6.51% Rp ¼4.85% Re ¼ 6.14% S ¼1.06 χ2 ¼1.12 Rwp ¼6.12% Rp ¼ 4.83% Re ¼ 6.79% S¼ 0.90 χ2 ¼ 0.81 Rwp ¼7.19% Rp ¼ 5.31% Re ¼ 6.78% S ¼ 1.06 χ2 ¼ 0.89 Rwp ¼7.92% Rp ¼ 6.29% Re ¼8.06% S ¼0.98 χ2 ¼ 0.97

1.89 1.90 2.03 2.05 2.10

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M. Sundararajan et al. / Materials Science in Semiconductor Processing 40 (2015) 1–10 800

600

Yobs Ycal Yobs-Ycal Braggs Position

CoF1

700

500

500

Intensity (arb.units)

Intensity (arb.units)

600

400 300 200

Yobs Ycal Yobs-Ycal Braggs Position

CoZF2

400

300

200

100

100 0

0

-100 10

20

30

40

50

60

70

80

10

20

30

2 theta (degree) 900 800

500

60

70

80

Yobs Ycal Yobs-Ycal Braggs Position

CoZF4

450 400

Intensity (arb.units)

600

Intensity (arb.units)

50

550

Yobs Ycal Yobs-Ycal Braggs Position

CoZF3

700

500 400 300 200

350 300 250 200 150 100

100

50

0

0

-100

-50 10

20

30

40

50

60

70

80

10

20

30

2 theta (degree) 450

40

50

60

70

80

2 theta (degree) Yobs Ycal Yobs-Ycal Braggs Position

CoZF5

400 350

400

Yobs Ycal Yobs-Ycal Braggs Position

CoZF6

350 300

300

Intensity (arb.units)

Intensity (arb.units)

40

2 theta (degree)

250 200 150 100

250 200 150 100

50

50

0

0

-50 10

20

30

40

50

60

70

2 theta (degree)

80

10

20

30

40

50

60

70

80

2 theta (degree)

Fig. 3. Rietveld refined XRD patterns for (a) CoF1, (b) CoZF2, (c) CoZF3, (d) CoZF4, (e) CoZF5 and (f) CoZF6 samples.

et al. [22]. As the Zn ion concentration increases, lattice parameter also increases and obeys Vegard's Law as shown in Fig. 2. The linear increase in the lattice parameter with increasing Zn2 þ concentration indicate the occurrence of lattice expansion without disturbing the lattice symmetry [23]. This is due to the fact that the size of Zn2 þ ions radius

(0.82 Å) is larger than the radius of Co2 þ ions radius (0.78 Å) [24]. Rietveld refinement analyses were performed for all the pure and zinc doped cobalt ferrite samples using FULLPROF program [25] to characterize the structural aspect of the material. The refinements were carried out in the Fd3m space

M. Sundararajan et al. / Materials Science in Semiconductor Processing 40 (2015) 1–10

5

Fig. 4. HR-SEM images of (a) CoF1, (b) CoZF2, (c) CoZF3, (d) CoZF4, (e) CoZF5 and (f) CoZF6 samples.

group. As shown in Fig. 3, the observed XRD pattern of the samples matches well with the calculated one. No other new phases were observed. Fig. 3 suggests that the observed and

the calculated profile patterns match perfectly. The refinement confirmed the spinel-type structure of the samples. The χ2 values for all the ferrite samples (zinc fraction 0–0.5) given in

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Fig. 5. Energy dispersive X-ray analysis of (a) CoF1, (b) CoZF2, (c) CoZF3, (d) CoZF4, (e) CoZF5 and (f) CoZF6 samples.

Table 1 are closer to 1. The goodness of fit index (S) is calculated from S¼Rwp/Re, where Rwp and Re are the weighted profile and expected weighted profile reliability patterns respectively. The value of ‘S’ around ‘1’ also indicates the excellent goodness of fit and confirms that the refinements made are accurate. 3.2. High resolution scanning electron microscopy (HR-SEM) analysis The surface morphology admits the agglomerated coalescence behavior of the particles as seen in Fig. 4(a)–(f). This agglomeration may be due to the interfacial surface tension phenomenon. The conversion of microwave energy into internal heat energy by strong intermolecular friction

would have resulted in the agglomeration and coalescence of the particles during the course of microwave irradiation. The EDX spectra of the samples are depicted in Fig. 5(a)–(f). The peaks corresponding to Co, Fe and O elements are observed in Fig. 5(a), whereas the peaks due to Zn atoms are observed in all the doped CoFe2O4 samples (Fig. 5(b)– (f)). The zinc fraction with respect to cobalt fraction is achieved as evidenced in the values given in the inset table in Fig. 5(a)–(f). 3.3. UV–visible diffused reflectance spectroscopy (DRS) analysis The diffuse reflectance spectra (DRS) is a standard tool to determine the optical band gap of the nanoparticles.

M. Sundararajan et al. / Materials Science in Semiconductor Processing 40 (2015) 1–10

7000

8000

CoF1

7

CoZF2

6000 6000

5000 4000

4000 3000 2000

2000

1000 0 2

3

4

5

6

0 2

3

4

5

6

3

4

5

6

3

4

5

6

7000

CoZF3

2500

CoZF4 6000 5000

(F(R)hν)2

2000

4000

1500

3000 1000 2000 500

1000

0 2 2000

3

4

5

6

0 2

CoZF5 5000

1500

CoZF6

4000

3000

1000

2000 500 1000

0 2

3

4

5

6

0 2

hν (eV) Fig. 6. (F(R)hν)2 versus hν plots for (a) CoF1, (b) CoZF2, (c) CoZF3, (d) CoZF4, (e) CoZF5 and (f) CoZF6 samples.

The band gap values of cobalt ferrites were calculated using the Tauc relation [26]. In general Kubelka–Munk function F(R) is applied to convert the diffused reflectance (R) in accordance with Eq. (5) p ¼ FðRÞ ¼

ð1  RÞ2 2R

ð5Þ

where F(R) is Kubelka–Munk function, R, the reflectance and α, is the absorption coefficient. Thus, the Tauc relation becomes, FðRÞhν ¼ Aðhν Eg Þn

ð6Þ

where n ¼1/2 and 2 represents direct and indirect transitions, thereby giving direct and indirect band gaps

respectively. The plots of (F(R)hν)2 versus hν for all the samples are shown in Fig. 6(a)–(f). Extrapolation of linear regions of these plots to (F(R)hν)2 ¼0 gives the direct band gap values [27]. The estimated band gap values of Co1  xZnxFe2O4 (x¼ 0, 0.1, 0.2, 0.3, 0.4 and 0.5 fractions) are 1.88 eV, 1.89 eV, 1.90 eV, 2.03 eV, 2.05 eV and 2.10 eV respectively. The value of direct band gap obtained for pure cobalt ferrite in the present study is lower than the bulk, which is around 1.95 eV [28]. Further, on doping with zinc, the band gap goes on increasing with increase in Zn (x ¼0.1 to x¼0.5) mole percentage in cobalt ferrite matrices [29]. The energy gap value increase is attributed to the quantum confinement phenomenon taking place at the nano-regime. The decrease in the crystallite size with

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(e)

the tetrahedral sites of Fe3 þ –O2  respectively [34,35]. The band at 382 and 296 cm  1 is attributed to the octahedral group of Co2 þ –O2  respectively [36].

(d)

3.5. Magnetization analysis

(f)

Transmittance (%)

(c) (b) (a)

4000

3600

3200

2800

2400

2000

1600

1200

800

400

Wavenumber (cm-1) Fig. 7. FTIR spectra of Co1  xZnxFe2O4 for (a) CoF1, (b) CoZn2, (c) CoZn3, (d) CoZF4, (e) CoZF5 and (f) CoZF6 samples. 80

CoF1 CoZF2 CoZF3 CoZF4 CoZF5 CoZF6

Magnetization (emu/g)

60 40 20 0 -20 -40 -60 -80 -15000

-10000

-5000

0

5000

10000

15000

Applied field (Oe) Fig. 8. Magnetic hysteresis of Co1  xZnxFe2O4 samples measured at 300 K from  15 kOe to þ15 kOe.

increasing the optical band gap confirms quantum size effect [30]. 3.4. FT-IR spectra The FT-IR spectra of pure and zinc substituted cobalt ferrite spinels are recorded in the 4000–400 cm  1 region (Fig. 7). All the samples exhibiting broad band around 3436 cm  1 is assigned to the stretching vibrations of O–H groups of water molecule [33]. The peak observed at 2350 cm  1, is assigned to H–O–H bending vibration of the free or absorbed water [31]. The peak observed at 1630 cm  1 is assigned to C ¼O stretch, respectively [32]. The bands observed at 1390 cm  1 and 1101 cm  1 is assigned to the retained water in the nanoparticles by the preparation technique adopted [33]. The band at about 569 cm  1 is due to the intrinsic stretching vibrations of

The hysteresis loops of Co1  xZnxFe2O4 samples prepared by microwave combustion technique were measured at 300 K from  15 kOe to þ 15 kOe applied magnetic field range. The shape of the M–H curve in Fig. 8 is narrow and indicate that the ferrites fall under the soft ferrite category. The magnetic properties, such as, saturation magnetization (Ms), coercivity (Hc) and remanence magnetization (Mr) were calculated from the hysteresis curves. The Ms, Hc, and Mr behavior varied as a function of zinc fraction as seen in Fig. 9(a)–(c). All the Ms, Hc and Mr values suddenly decreased from 65.84 to 41.5 emu/g, 770.32 to 435.30 Oe, 26.82 to 9.87 emu/g respectively at x¼0.1 zinc fraction. However, the Ms and Mr values gradually increases from 42.49 to 59.42 emu/g, 10.87 to 15.09 emu/g from x ¼0.2 to 0.5 respectively. The observed drop in the magnetization values is attributed to the following facts (i) decrease in the magnetocrystalline anisotropy, (ii) non-stoichiometry compositional change, (iii) size decreasing effect, due to Zn2 þ doping, and (iv) increase in the surface spin canting effect [37]. A further gradual increase in the saturation magnetization and remnants values beyond x ¼0.3 shall be due to the facts explained by Tahar et al. [36] and Zare et al. [38]. On the basis of (i) transition from Neel's like collinear ferrimagnetic structure to a Yafet–Kittel like canting behavior and (ii) departure of the structure from thermodynamical stable cation distribution over the spinel sub lattice. Similar kind of simultaneous increase and decrease in the magnetization values with increasing zinc composition in the cobalt ferrite systems is in agreement with the earlier reports [39–45]. 4. Conclusions Nanostructured pure and zinc substituted cobalt ferrite was successfully prepared by the microwave combustion method using L-arginine as a fuel. The XRD pattern matched well with the JCPDS card number 22-1086 signifying the cubic spinel structure with Fd3m space group. Rietveld refinement analyses confirmed the spinel-type structure of the samples indicating the absence of any other new phases. The lattice parameter increased with increasing zinc mole percentage, due to the substitution of Zn (larger ionic radius) in the cobalt sites (smaller ionic radius). SEM images showed the presence of aggregated nanoparticles. The direct band gap (Eg) energy of pure cobalt ferrite nanoparticles is 1.88 eV. Quantum confinement phenomena were observed with increasing the zinc mole percentage in the doped cobalt ferrite system. FT-IR spectra showed the band at about 569 cm  1 that is due to the intrinsic stretching vibrations of the tetrahedral sites of Fe3þ – O2 respectively. The band at 382 and 296 cm  1 is attributed to the octahedral group of Co2þ –O2 respectively. The saturation magnetization (Ms) of pure and zinc doped cobalt ferrites were due to the cation redistribution in the nanoregime. The results obtained in the present study suggests that

M. Sundararajan et al. / Materials Science in Semiconductor Processing 40 (2015) 1–10

9

70

Saturation magnetization, Ms (emu/g)

800

Coercivity (Oe)

700

600

500

400

300 0.0

0.1

0.2

0.3

0.4

0.5

65

60

55

50

45

40

0.0

0.1

Zinc fraction

0.2

0.3

0.4

0.5

Zinc fraction

Remanant magnetization, Mr (emu/g)

28

24

20

16

12

8 0.0

0.1

0.2

0.3

0.4

0.5

Zinc fraction Fig. 9. Variation of (a) coercivity, (b) saturation magnetization and (c) remnant magnetization for Co1  xZnxFe2O4 (0 rx r 0.5).

the Co1 xZnxFe2O4 (0rxr0.5) nanostructures can be prepared by microwave combustion technique employing Larginine as fuel and can be a potential candidate in magnetic electronics and optoelectronic applications.

Acknowledgment The Authors highly thank the VIT University management, Chennai for providing the financial assistance through Research Associate Fellowship (Ref: VIT/CC-Estt/2013/2207.5 ) to carry out the research program. References [1] Z. Liang, J. Guang-Fu, Z. Feng, G. Zi-Zheng, Chin. Phys. B 20 (2011) 047102–047107. [2] K.E. Sickafus, J.M. Wills, N.W. Grimes, J. Am. Ceram. Soc. 82 (1999) 3279–3292. [3] A. Nakatsuka, Y. Ikeda, Y. Yamasaki, N. Nakayama, T. Mizota, Solid State Commun. 128 (2003) 85–90.

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