Investigation of structural, thermal and magnetic properties of cadmium substituted cobalt ferrite nanoparticles

Investigation of structural, thermal and magnetic properties of cadmium substituted cobalt ferrite nanoparticles

Superlattices and Microstructures 82 (2015) 165–173 Contents lists available at ScienceDirect Superlattices and Microstructures journal homepage: ww...

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Superlattices and Microstructures 82 (2015) 165–173

Contents lists available at ScienceDirect

Superlattices and Microstructures journal homepage: www.elsevier.com/locate/superlattices

Investigation of structural, thermal and magnetic properties of cadmium substituted cobalt ferrite nanoparticles Ch. Venkata Reddy a, Chan Byon a, B. Narendra b, D. Baskar b, G. Srinivas b, Jaesool Shim a,1, S.V. Prabhakar Vattikuti a,⇑ a b

Department of Mechanical Engineering, Yeungnam University, Gyeongsan 712-749, Republic of Korea Department of Physics, K L University, Vaddeswaram, A.P. 522 502, India

a r t i c l e

i n f o

Article history: Received 23 January 2015 Accepted 4 February 2015 Available online 21 February 2015 Keywords: Ferrites X-ray diffraction Magnetic properties FT-IR Calcination temperature

a b s t r a c t Cd substituted Cobalt ferrite nano particles are synthesis using coprecipitation method. The as prepared samples are calcinated at 300 and 600 °C respectively. The existence of single phase spinal cubic structure of the prepared ferrite material is confirmed by the powder XRD measurement. The surface morphology images, compositional features are studied by SEM with EDX, and TEM. From the FT-IR spectra the absorption bands observed at 595 and 402 cm1 are attributed to vibrations of tetrahedral and octahedral complexes respectively. From the VSM data, parameters like magnetization, coercivity, remanent magnetization and remanent squareness are measured. The saturation magnetization value is increases with increasing calcination temperature. The DSC and TG–DTA curves reveal that the thermal stability of the prepared ferrite nanoparticles. The calcination temperature affects the crystallite size, morphology and magnetic properties of the samples. Ó 2015 Elsevier Ltd. All rights reserved.

⇑ Corresponding author at: School of Mechanical Engineering, Yeungnam University 214-1 Dae-dong Gyeongsan-si, Gyeongsangbuk-do 712-749, Republic of Korea. Mobile: +82 10 4017 8527; fax: +82 53 810 4627. E-mail addresses: [email protected] (J. Shim), [email protected] (S.V. Prabhakar Vattikuti). 1 Co-corresponding author. http://dx.doi.org/10.1016/j.spmi.2015.02.014 0749-6036/Ó 2015 Elsevier Ltd. All rights reserved.

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1. Introduction In the recent years, the synthesis of composite magnetic nanoparticles has been received increasing attention due to their properties [1–4]. Spinel structure ferrites are a very significant group of magnetic materials due to their chemical, thermal strengths, cubic magneto crystalline anisotropy [3], moderate saturation magnetization, electrical insulation and wear resistance [5–7]. Ferrite has attracted considerable attention in the field of technological application as well in a wide range of frequencies. An inverse spinel structure of CoFe2O4 is one of the most significant ferrite, where oxygen atoms make up an FCC lattice and one half of Fe3+ ions occupies the tetrahedral A sites and the other half, together with Co2+ ions locate at the octahedral B sites. It is a ferromagnetic material with a Curie temperature (TC) around 793 K which distinguishes it from other spinel ferrites. Moreover, cobalt ferrite nanoparticles are known to be a photo magnetic material it shows an interesting light-induced coercivity change [8,9] and as active material for lithium ion battery [10,11]. The physical properties of the ferrites depend strongly on the shape and size of the nanoparticles [9,12,13]. To the best of our knowledge, very few research groups were reported on the Cd substituted cobalt ferrite4 materials. In details, Farea et al. studied the electrical properties of cadmium cobalt ferrite and their results implies Cd atoms are plays an important role in enhancement of the dielectric constants e0 and e00 , the loss tangent tan d, and the AC conductivity rac [14–16]. Narendra et al. reported on cadmium-substituted CoFe2O4 nanoparticles exhibits the super paramagnetic behavior [17]. Therefore, this observation is attracting to widely focus on these materials. In addition, Gabr et al. investigated the conductance properties and the catalytic decomposition of 2-propanol of CdCoFe materials [18]. Nikumbh et al. reported on cadmium cobalt ferrite with compositional changes of cadmium and cobalt; the magnetic coupling strengthens A–B interactions takes place at dopant concentration above x P 0.6 [19]. The properties of ferrites strongly depend on the chemical composition, the electronic structure of the magnetic ions, preparation conditions, and the crystal structure of the lattice [15,20–22]. In fact, preparation methods of cobalt ferrite nanoparticles are diverse, such as microemulsions [23], a microwave hydrothermal flash method [24] and polymerized complex method [25]. However, these methods have low yield rate and they require a long processing time. In contrast, the chemical synthesis from aqueous solutions is a relatively simple method that is suitable for mass production. Moreover, the preparation parameters such as the concentration, pH, and complexing agent are easily controllable [26]. In the present work, we report the preparation of Cd0.5Co0.5Fe2O4 nanostructures (in the forms of nanoparticles) by co-precipitation method using a solution that contained NaOH, Oleic acid is used for coated samples. In order to find the temperature effect on structural, morphology, thermal and magnetic properties, the prepared Co0.5Cd0.5Fe2O4 nanoparticles are analyzed using X-ray diffraction, SEM with EDX, TEM, FT-IR, DSC,TG–DTA and VSM techniques.

2. Experimental procedure The chemical co-precipitation method is used for the preparation of Cd0.5Co0.5Fe2O4 nanoparticles. Stoichiometric amounts of aqueous solutions containing CoCl2, CdCl2, and FeCl3 (100 mL of 0.5 M CoCl2, 100 mL of 0.5 M CdCl2, and 100 mL of 2 M FeCl3) are mixed and kept at 60 °C. This mixture is added to a boiling solution of NaOH (0.63 M dissolved in 1200 mL of distilled water). The solutions are maintained at 85 °C for 1 h to adjust the pH to around 12. The pH of the solution is reduced to 10.5 for surfactant coating, for which oleic acid (C18H34O2) is used. The oleic acid is heated with the NaOH solution to convert the oleic acid to sodium oleate. The sodium oleate solution is transfer to a glass beaker and stirred for 3 h. Surfactant coating is carried out at a temperature of about 100 °C for 1 h. Dilute HCl is added to coagulate the oleic-acid-coated particles. After decantation, the product is washed with distilled water to remove soluble impurities. The coated particles were collected after removing the excess water by washing with acetone. The as-prepared samples are then sintered at 300 °C and 600 °C respectively for 1 h hereafter samples named as S1 and S2. The cadmium cobalt ferrite nano particles are characterized using the Powder X-ray diffraction (XRD) pattern using Cu Ka radiation on PANalytical X’Pert PRO diffractometer. The Microstructural

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features are carried out using SEM: CARL ZEISS EVO18. The elemental composition of sample is analyzed using EDX interfaced with SEM. The transmission electron Microscope (TEM) images are recorded using TEM HITACHI H-7600 instrument. The FT-IR analysis is carried out on Perkin Elmer Spectrum for the prepared powders using KBr. The DSC measurements are recorded on NETZSCH DSC 204. The TG–DTA measurements are recorded on SDT Q 600 instrument. The magnetic measurements for the synthesized ferrites are taken on Vibrating Sample Magnetometer (VSM; ADE/DMS model EV73). 3. Results and discussions The powder XRD patterns of Co0.5Cd0.5Fe2O4 nanoparticles are shown in Fig. 1. The samples S1 and S2 consisted of well crystalline Co0.5Cd0.5Fe2O4 phase. The Powder XRD patterns of samples S1 and S2 confirms the formation of cubic spinel structure. The XRD patterns show the planes of a cubic unit cell (2 2 0), (3 1 1), (2 2 2), (4 0 0), (4 2 2), (5 1 1) and (4 4 0) respectively. The planes (2 2 0) and (4 2 2) observed from the X-ray diffraction are sensitive to the cations distribution on tetrahedral sites, while the plane (2 2 2) is sensitive to the cation on octahedral sites [27]. The plane (3 1 1) denotes the spinel phase. The XRD patterns of the nanoparticles reveal that all the diffraction peaks correspond to the cubic spinel lattice of CoFe2O4 (JCPDS File No. 22–1086). This confirms the formation of cubic spinel structure of single phase ferrite without impurities. The average crystallite sizes are calculated from the line broadening of intense peak (3 1 1) using the Scherrer relationship: D = 0.9k/bcos h, where D is the average crystallite size, k is wavelength of the radiation used, b is the half maximum line width, and h is the angle of diffraction. The average crystallite sizes are 8 and 14 nm (within an error of ±2 nm). The average particle size increases with increasing the calcination temperature. The strain (e) and dislocation density (d) are evaluated to obtain more information about the structural characteristics of the prepared ferrite nanoparticles [28]. The average strain (e) of the ferrite nanomaterial is calculate using the Stokes–Wilson equation, estr = (b/4) tan h. The dislocation density (d) is evaluate from the relation d = 15e/aD. The average lattice strain and dislocation density of the Cd0.5Co0.5Fe2O4 nanoparticles are estimated. The strain value is increases with increasing the calcination temperature [29]. The grain sizes, strain, and dislocation density of the Cd0.5Co0.5Fe2O4 nanoparticles are given in Table 1. The average particle size increases with increasing the calcination temperature.

Fig. 1. X-ray diffraction patterns of Co0.5Cd0.5Fe2O4 nanoparticles (a) sample S1 and (b) sample S2.

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Table 1 The grain sizes, strain, dislocation density of Cd0.5Co0.5Fe2O4 nanoparticles. Sample

D ± 2 nm

Strain (e)

Dislocation density (d) (lines/m)

S1 S2

8 14

4.75  103 8.78  103

10.6  1015 11.2  1015

Fig. 2. SEM images of Co0.5Cd0.5Fe2O4 nanoparticles (a) sample S1; (b) sample S2 and EDX spectra (a) sample S1 and (b) sample S2.

The surface morphology and the EDX spectra of the Co0.5Cd0.5Fe2O4 are shown in Fig. 2. In the sample S1, large size flake like structure is observed (shown in Fig. 2(a)). In the sample S2, grains like particles are observed (shown in Fig. 2(b)). It is noticed that the morphology of the sample S2 has been affected by the sintered temperature. In the sample S2 the net magnetization may be increases due to the particle size. The grain size determined by XRD is different from the grain sizes observed from SEM. This indicates the grains seen in the SEM are the domains formed by aggregation of nanosize crystallites [28]. Elemental composition analysis of the Cd0.5Co0.5Fe2O4 nanoparticle specimens are carried out using energy dispersive spectroscopy (EDS). The EDX spectra give information about the chemical composition of the elements present from the surface to the interior of the solids, and they are used to confirm the homogeneity of the investigated samples. The EDX spectra of the sample S1 and S2 are shown in Fig. 2(c) and (d). From the EDX results, the spectra indicated the presence of Fe, Co, Cd, and O as the major elements in the synthesized material with no impurities are observed along with elemental mapping. Thus, the results indicate that most of the undesired precursor materials have been completely removed from the product during the calcination process. Fig. 3 shows TEM images of the Cd0.5Co0.5Fe2O4 nanoparticles. The nanoparticles have a regular cubic spinel structure. This indicates that the ferrite particles are uniform in both morphology and

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Fig. 3. TEM images of Co0.5Cd0.5Fe2O4 nanoparticles (a), (b) sample S1 and (c), (d) sample S2.

particle size distribution. The particle sizes were estimated from TEM to be around 9 and 15 nm (error ±2 mn), which is good agreement with the XRD measurements. Particle agglomeration takes place due to the magneto-static interaction between particles [30] or the nanoparticles experiencing a permanent magnetic moment proportional to their volume [31]. The morphology and size of the materials are significantly affected by the calcination temperature. In addition, as the annealing temperature is increases from 300 °C to 600 °C, the particle size is increases, which is also confirmed by XRD measurement. The FT-IR Spectra of Co0.5Cd0.5Fe2O4 nanoparticles are shown in Fig. 4. In general, the FT-IR analysis shows two distinct frequency regions from 4000 to 1000 cm1 and from 1000 to 400 cm1 respectively. The absorption bands in the range of 400–1000 cm1 corresponds to the stretching vibration of tetrahedral and octahedral sites. These two bands are responsible for the formation of ferrite (spinal structure) material. The bands are observed at 595 and 402 cm1 which are related to the stretching vibrations of tetrahedral and octahedral sites in both samples. The stretching vibration of the tetrahedral metal–oxygen band (FeAO) is related to higher frequency absorption band, and in octahedral sites it is related to the lower frequency band (CdAO) [32]. The bands are observed at 1426 and 2930 cm1 in sample S1 indicates the presence of [email protected], and stretching vibration of the CAH mode. The presence of these two bands may be due to the residual of chemicals. In the sample S2 these bands are disappeared when it is sintered at 600 °C. The bands observed at 3443 cm1 in the samples S1and S2 are assigned to the stretching and bending vibrations of the HAOAH bond, respectively [33]. This shows the physical adsorption of H2O on the surfaces.

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Fig. 4. FT-IR spectra of Co0.5Cd0.5Fe2O4 nanoparticles (a) sample S1 and (b) sample S2.

0.8

1.0

(b)

0.7

0.8

Peak 96.2 οC

Heat Flow (mW/mg)

Heat Flow (mW/mg)

Peak 59.0 οC

(a)

0.6 Area= 33.54 J/g 0.4

0.6

0.5

0.4

0.2 Area= 101.7 J/g

0.3 0.0 0

50

100

Temperature

150

(οC)

200

0

20 40

60

80 100 120 140 160 180 200

Temparature (οC)

Fig. 5. DSC curves of Co0.5Cd0.5Fe2O4 nanoparticles (a) sample S1 and (b) sample S2.

The DSC curves of Co0.5Cd0.5Fe2O4 nanoparticles are shown in Fig. 5(a) and (b). Only one exothermic peak was observed in the DSC curves at 96.2 and 59.0 °C in both samples. In the sample S2 the particle size increased and crystallinity of the sample increased, this is confirmed by the XRD. As revealed by DSC curves, the peak at 96.2 °C is broad and peak at 59.0 °C is sharp and strong. The strong exothermic peak indicates temperature which corresponds to complete melting in Co0.5Cd0.5Fe2O4 spinel and the energy that the melting transition needs in order to occur. This is the enthalpy of the transitions and it is associated with the crystalline of materials. The thermal stability of Cd0.5Co0.5Fe2O4 nanoparticles are investigated using TG–DTA. The TGA– DTA curves of Cd0.5Co0.5Fe2O4 nanoparticles are shown in Fig. 6. The TGA curve shows that a total weight loss of about 28.62% occurred; this can be ascribed to the decomposition of oxides, there is a negligible weight loss occurred after 590 °C. This confirms the formation of a stable phase of Cd0.5Co0.5Fe2O4 materials. The DTA curve exhibits a large exothermic peak starting below 100 °C, which can be ascribed to the evaporation of absorbed water and trapped solvent from the precursor

102 100 98 96 94 92 90 88 86 84 82 80 78 76 74 72 70

171

0.16 0.14 0.10 0.08 0.06 0.04 0.02

o

0.12

Deriv.Weight (%/ C)

Weight (%)

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0.00 -0.02 0

200

400

600

800

1000

1200

Temperature (oC) Fig. 6. TG–DTA curves of Co0.5Cd0.5Fe2O4 nanoparticles.

3

(b)

2

M (emu/g)

1

(a) 0

-1

-2

-3 -20000 -15000 -10000 -5000

0

5000 10000 15000 20000

H (Oe) Fig. 7. Hysteresis loop of the Co0.5Cd0.5Fe2O4 nanoparticles (a) sample S1 and (b) sample S2.

nanoparticles. The prominent exothermic peak at 335 °C corresponds to the decomposition of inorganic salts. The exothermic peaks around 628 °C and 810 °C correspond to the decomposition of oxidative. This confirms that the majority of the mass loss occurs under 628 °C and allows for optimization of the heat treatment program. The magnetic properties of the Cd0.5Co0.5Fe2O4 nanoparticles are studying by the VSM technique at the room temperature under an applied magnetic field of 18 K Oe. The hysteresis curve of Co0.5Cd0.5Fe2O4 nano particles are shown in Fig. 7. The different values of the saturation magnetization (Ms), remanence magnetization (Mr), and coercivity (Hc) of the Cd0.5Co0.5Fe2O4 nanoparticles have been estimated and are given in Table 2. The changes in exchange interaction between tetrahedral and octahedral sub-lattices indicate the dependence of the saturation magnetization and magnetic

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Table 2 Coercivity (Hc), remanence magnetization (Mr), saturation magnetization (Ms), squareness, anisotropy constant (K) and magnetic moment (gB) (bohr magneton) of Cd0.5Co0.5Fe2O4 nanoparticles. Sample

Hc (Oe)

Mr (emu/g)

Ms (emu/g)

Mr/Ms (emu/g)

K (erg/Oe)

gB

S1 S2

40.84 65.852

0.0126 0.0225

0.433 2.265

0.0291 0.0100

18.04 152.19

0.0206 0.1060

moment with respect to their grain size [34]. Canted spin can also label the decrease in the saturation magnetization in the case of the nanoparticles [35,36]. For example, when samples are calcinated at lower temperatures, a large proportion of crystal defects and dislocations can occur within the lattice. Due to this, significant reduction of the magnetic moment occurs within the particles as a result of magneto crystalline anisotropy distortion [37]. The magnetic moment of the samples has been calculated, and the results are tabulated in Table 2. These results were obtained using the Bohr magneton (lB) based on the following relationship [38]: gB = M  Ms/5585, where M is the molecular weight of the composition, and Ms is the saturation magnetization (emu/g). Interestingly, the calculated magnetic moment value (Table 2) is increases with the annealing temperature increases. From the values of coercivity (Hc) and the saturation magnetization (Ms), the value of the anisotropy constant, K, can be calculated using the following relation [39]: Hc = 0.98K/Ms. K increases with increasing the annealing temperature (Table 2), which may be attributed to the lower coercivity of the Cd0.5Co0.5Fe2O4 nanoparticles [40]. The magnetization increases with increasing annealing temperature, which may be explained as follows. (i) The grain size of the prepared material increases, and the microstructure becomes well crystallized. (ii) Because of the particle size of the prepared samples, the number of grain boundaries increases, leading to increasing volume fraction of the surface and an increased interface as well, thus supplying more pinning sites for domain walls [41–43]. The smaller value of saturation magnetization is observed in the present work; due to the maximum Fe3+ ion concentration on tetrahedral sites. Since Cd2+ ions are non-magnetic ions, due to the substitution of Cd2+ ions the hysteresis parameters values are found low. In order to take into account, for both the samples the obtained coercive field (Hc) is small; these facilitate that the present synthesized materials are promising candidate to use in development of actuators and high-density data storage device applications [44].

4. Conclusions In the present study, we have synthesized samples of Co0.5Cd0.5Fe2O4 nanoparticles using co-precipitation method. The reflected peaks from the powder XRD patterns exhibit single phase spinel cubic structure. The SEM micrograph shows grains and flakes like surface morphology. The FT-IR spectra confirmed that the fundamental vibrations of host material. The DSC curves reveal the thermal stability of ferrite material. The particle size, magnetization, and coercivity of the samples increase with the increasing annealing temperature. The room-temperature magnetization measurement was confirmed that the saturation magnetization increases with increasing the particle size. Interestingly, the coercive field is obtained low for both the samples, which facilitate that the present synthesized nanoparticles are promising candidate to use in development of high-density data storage device and actuators applications. The calcination temperature influences the particle size and magnetic properties of the prepared ferrites. The prepared material shows typical super paramagnetic behavior due to its lower coercivity. Acknowledgement This work was supported by the National Research Foundation of Korea (NRF) funded by the Korea government (MEST) (NRF-2012R1A1A2009392).

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