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Single Step Synthesis and Characterisation of Nanocrystalline Cobalt Ferrite by Auto-Combustion Method
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 2 (2015) 3605 – 3609
4th International Conference on Materials Processing and Characterization
Single Step Synthesis and Characterisation of Nanocrystalline Cobalt Ferrite by Auto-Combustion Method T. Shanmugavela,*, S. Gokul Rajb, G. Rajarajanc, G. Ramesh Kumard, G. Boopathie a
Department of Physics, Excel Engineering College, Komarapalayam, Namakkal -637303, India b Department of Physics, Vel Tech University, Avadi, Chennai 600 062 India c Department of Physics, Selvam College of Technology, Namakkal-637005 India d Department of Physics, University College of Engineering, Anna University Chennai, Arni 632317, India e Department of Physics, Presidency College (Autonomous), Chennai - 600005, India *Email: [email protected] / [email protected]
Abstract Nano-Crystalline cobalt ferrite nanoparticles were synthesized from an aqueous solution containing metal nitrates and citric acid as a capping agent by an auto-combustion method followed by calcined at high temperature at 600ºC. The structural characteristics and single phase formation of the calcined sample is determined by X-ray diffraction (XRD). Magnetization measurements were obtained at room temperature by using a vibrating sample magnetometer (VSM), which showed that the calcined sample exhibited typical magnetic behaviour. © 2014 The Authors. Elsevier Ltd. All rights reserved. © 2015 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the conference committee members of the 4th International conference on Selection and peer-review under responsibility of the conference committee members of the 4th International conference on Materials Materials Processing and Characterization. Processing and Characterization. Keywords: Nano-crystalline Cobalt ferrite; Auto-combustion synthesis; XRD analysis; FTIR; VSM; SEM;
1. Introduction Recently metal–oxide nanoparticles have been the subject of much interest because of their unusual optical, electronic and magnetic properties, which often differ from the bulk. Cobalt ferrite, CoFe2O4, is a well-known spinel ferrite and magnetic material with high crystalline anisotropy, high coercivity, and moderate saturation magnetization. Nanocrystalline cobalt ferrites have been synthesized using a variety of physical methods, including mechanochemical
2214-7853 © 2015 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the conference committee members of the 4th International conference on Materials Processing and Characterization. doi:10.1016/j.matpr.2015.07.106
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T. Shanmugavel et al. / Materials Today: Proceedings 2 (2015) 3605 – 3609
[1], and thermal decomposition [2]. Wet chemical methods are particularly interesting for their versatility, lowtemperature preparation, and potential for production scale up. CoFe2O4 have been obtained by co-precipitation [3], hydrothermal [4], sol–gel [5], sonochemical [6], and micelle micro-emulsion [7] approaches. In all applications, the nanoparticle preparation method is of primary importance for the particle size distribution, shape, surface characteristics and magnetic properties. Cobalt nanocrystalline ferrites having wide applications in the field of electronic devices, ferrofluids, magnetic drug delivery, microwave devices, high-density information storage, catalysts and gas sensors [8-10]. Hence, they have been widely used in paint and coating systems [11]. Present work, we prepared CoFe2O4 using auto-combustion method, a simple, non-grinding, economic and versatile technique, which can be extended for large-scale production [12]. The prepared powder shows excellent magnetic properties and an average grain size of 35nm is produced in single step. 2. Experimental 2.1. Materials Iron nitrate(III) Fe(NO3)3·9 H2O, and cobalt nitrate(II) Co(NO3)2·6H2O, were purchased from Merck with purities exceeding 98.3%.Citric acid was purchased from Sigma Aldrich and was used without further purification. An appropriate amount of iron nitrate and cobalt nitrate were dissolved in to deionized water in the ratio (Fe:Co=2:1), then aqueous solution was continuously stirred by a magnetic stirrer. Chelating agent (citric acid) is added to produce the metal spinel ferrite with proposed ratio and it was added with nitrate aqueous solution until viscous resin was obtained. The resulting powder is calcined to high temperature 600ºc. 2.2. Characterization The characterization of the prepared cobalt ferrite nanoparticles was conducted by using various techniques to verify the particle size and distribution and to explore other parameters of interest. The structure of the CoFe 2O4 nanoparticles was characterized by the XRD technique using a Shimadzu diffractometer (model XRD 6000) using C u Kߙ (0.154 nm) radiation to generate diffraction patterns from the crystalline powder samples at ambient temperature over the 2 ߠ range from 10° to 80°. The Particle morphology was investigated by a Scanning Electron Microscope. Magnetic characterization of the cobalt ferrite nanoparticles was performed by using a vibrating sample magnetometer (VSM) (Lake Shore 4700) at room temperature with a maximum magnetic field of 10 kOe. 3. Result and Discussion Fig. 1 shows the powder XRD patterns of the CoFe2O4 obtained for calcined for 600°C. The characteristic peaks could be indexed for that cubic structure CoFe2O4, which is close agreement with the reported data (JCPDS File No. 03-0864). From that, it is known that the sample was pure CoFe2O4 crystals without impurity phases. Meanwhile, the reflection peaks become sharper and stronger with the increase of temperature. The peak broadening is purely due to the reduced particle size. The crystallite size of samples was determined from the broadening of cubic CoFe2O4 (311) X-ray spectral peaks using the Scherrer formula:[13] D = Kλ /β cos θ
[1]
4. where D is the crystallite size, λ the wavelength of the X-ray radiation, K usually taken as 0.89, and β is the line width at half maximum height, after subtraction of equipment broadening. Due to the annealing process results in a decrease in the defects, coalescence of crystallites, which in turns results in an increase in the average size of the nanoparticle [14].
3607
(311)
T. Shanmugavel et al. / Materials Today: Proceedings 2 (2015) 3605 – 3609
(440)
(511)
(422)
(400)
(222)
Intensity
(111)
(220)
Co600
JCPDS 03-0864
10
20
30
40
50
2 Theta
60
70
80
o
Fig.1. Powder X–ray diffraction patterns of (a) JCPDS 03-0864; (b) CoFe2O4 at 600 °C.
The morphology was examined by scanning electron microscopy (SEM) (Philips, XL30 EDAX model). Fig. 2 shows the FE-SEM image of CoFe2O4 nanoparticles. The structural morphology of the nanoparticles was investigated through FE-SEM[15]. It shows that the CoFe2O4 nanoparticle prepared by auto-combustion method have some agglomeration of the nanoparticle was observed. SEM images reveal that the samples’ surfaces exhibit welldefined crystalline nanoparticles of spherical shapes with soft agglomeration. The size of the particle, determined from the FESEM micrographs, is the order of 12–30nm. These values of particle size are in good agreement with the particle size calculated by Scherrer’s formula. Fig. 3 shows SEM micrographs of the powders.
Fig.2.FE-SEM for CoFe2O4 at 600 °C.
Fig.3.SEM for CoFe2O4 at 600 °C.
Fig. 4 shows the hysteresis loops of the samples calcined at 600°C. At room temperature, the sample exhibited hysteresis loop typical of magnetic behavior, indicating that the presence of an ordered magnetic structure can exist in the spinel system. It was known that the magnetic properties of nanosize particles depended on the preparation method and the particle size [16]. The values of saturation magnetization (Ms) of the samples at room temperature are 57 emu/g . The Ms value for CoFe2O4 sample is less than the value of saturation magnetization reported for bulk cobalt ferrite (80.8 emu/ g) [17]. While annealing generally decreases the lattice defects and strains, however, it can also cause coalescence of crystallites those results in increasing the average size of the nanoparticles. The magnetization sharply increases at low applied fields but at high field region it increases slowly and reach the saturation at l0 kOe magnetic field. As the temperature decreases, the coercivity values and saturation magnetizations of the samples increase. Due to the good ferromagnetic properties of samples, it is a capable material for high-density magnetic storage and medical diagnostics, etc.
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T. Shanmugavel et al. / Materials Today: Proceedings 2 (2015) 3605 – 3609
Co600
70 60 50
Momment (emu/gm)
40 30 20 10 0 -10
Ms= 56.71 emu/g Mr= 22.24 emu/g Hci= 1178.97 (Oe) Mr/Ms= 0.392
-20 -30 -40 -50 -60 -70 -10000
-5000
0
5000
10000
Field (Oe)
Fig. 4. VSM for CoFe2O4 at 600 °C.
4. Result and Discussion In conclusion, Nanocrystalline CoFe2O4 was synthesized by a low-temperature auto-combustion method utilizing only cobalt nitrate and iron nitrate as precursors, Citric acid as an agglomeration capping agent, and deionized water as a solvent. The modified citrate-gel method allows to mix the metal ions at atomic scale using stirring and to combine them through metal-citric gel network, leading to a perfect reaction between ions to form CoFe2O4. The X-ray diffraction analysis confirmed the cubic spinel phase formation and broadness of (3 1 1) indicates the smaller particle formation. The considerable broadening as well as the low intensity of all diffraction peaks indicate that the studied samples consist of quite small crystallites. There are no detectable traces of extra-crystalline phases. Scanning electron microscopy analysis reveals the highly agglomerated particles. This simple, cost-effective, and environmentally friendly method that produces no by-product effluents can be used to synthesize pure crystalline spinel cobalt ferrite nanoparticles. Furthermore, it can be extended to synthesizing other spinel ferrite nanoparticles of interest in nanotechnology. Acknowledgements One of the authors T. Shanmugavel wishes to thank to all the Management members and Department of Physics, and various department staff members of Excel Engineering College, Namakkal – 637 303, for providing a platform to perform the research. References [1] Y. Shi, J. Ding and H. Yin, 2000 , CoFe2O4 Nanoparticles Prepared by the Mechanical Method, Journal of Alloys and Compounds, Vol. 308, No. 1, pp. 290-295. [2] T. Hyeon, Y. Chung, J. Park, S.-S. Lee, Y.-W. Kim, B.H. Park, 2002, synthesis of high crystalline and monodisperse cobalt ferrite nanocrystals, J. Phys. Chem. B 106 6831–6833. [3] S. Komarneni, M.C. D’Arrigo, C. Leonelli, G.-C. Pellacani,1998, Microwave hydrothermal synthesis of nano ferrites. J. Am. Ceram. Soc. 81 ,3041–3043.
T. Shanmugavel et al. / Materials Today: Proceedings 2 (2015) 3605 – 3609
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[4] J.-G. Lee, J.-Y. Park, C.-S. Kim, 1998, Growth of ultra fine cobalt ferrite particles by their magnetic properties.,J. Mater. Sci. 33 ,3965– 3968. [5] J. de Vicente, A.V. Delgado, R.C. Plaza, J.D.G. Duran, F. Gonzalez- Caballero, 2000, Stability of cobalt ferrite colloidal particles. Effect of pH and applied magnetic fields,langmuir, 16(21), 7954-7961 . [6] M. Rajendran, R.C. Pullar, A.K. Bhattacharya, D. Das, S.N. Chintalapudi, C.K. Majumda,2001, , Magnetic properties of nanocrystalline CoFe2O4 powders prepared at room temperature: variation with crystallite size, J. Magn. Magn. Mater. 232 , 71–83. [7] S. Li, L. Liu, V.T. John, C.J. O’Connor, V.G. Harris,2001, Cobalt-ferrite nanoparticles: Correlations between synthesis procedures, structural characteristics and magnetic properties, IEEE Trans. Magn. 37 , 2350–2352. [8] F. Mazaleyrat, L.K. Varga, J. Magn. Magn. Mater. 215ˀ216 (2000) 253. [9] K. Yamaguchi, K. Matsumoto, T. Fujii, 1990, Magnetic anisotropy by ferromagnetic particles alignment in a magnetic field, J.Appl. Phys. 67 4493ˀ4495. [10] Y. Shahoo, A. Goodarzi, M.T. Swihart, J. Phys. Chem. B 109 (2005) 3879ˀ3885. [11] Z. Aixiang, X. Weihao, X. Jian, 2005, Electroless Ni–P coating of cenospheres using silver nitrate activator,Surf. Coat. Technol. 197 142ˀ 147. [12] J. F. Crider, Ceram. Eng. Sci. Proc. 3 (1982) 519. [13] H.G. Jiang, M. Rühle, E.J. Lavernia, J. Mater. Res. 14 (1999) 549. [14] T.P. Raming, A.J.A. Winnubst, C.M. van Kats, P. Philips, J. Colloid Interface Sci. 249 (2002) 346. [15] Manish Srivastava, S. Chaubey, Animesh K. Ojha, Investigation on size dependent structural and magnetic behavior of nickel ferrite nanoparticles prepared by sol–gel and hydrothermal methods, Materials Chemistry and Physics 118 (2009) 174–180. [16] Y. Ahn, E.J. Choi, S. Kim, H.N. Ok, Magnetization andM¨ossbauer study of cobalt ferrite particles from nanophase cobalt iron carbonate, Mater. Lett. 50 (2001) 47–52. [17] D.J. Craik, Magnetic Oxides, Part II, Wiley, London, 1975, p. 703.
ScienceDirect Materials Today: Proceedings 2 (2015) 3605 – 3609
4th International Conference on Materials Processing and Characterization
Single Step Synthesis and Characterisation of Nanocrystalline Cobalt Ferrite by Auto-Combustion Method T. Shanmugavela,*, S. Gokul Rajb, G. Rajarajanc, G. Ramesh Kumard, G. Boopathie a
Department of Physics, Excel Engineering College, Komarapalayam, Namakkal -637303, India b Department of Physics, Vel Tech University, Avadi, Chennai 600 062 India c Department of Physics, Selvam College of Technology, Namakkal-637005 India d Department of Physics, University College of Engineering, Anna University Chennai, Arni 632317, India e Department of Physics, Presidency College (Autonomous), Chennai - 600005, India *Email: [email protected] / [email protected]
Abstract Nano-Crystalline cobalt ferrite nanoparticles were synthesized from an aqueous solution containing metal nitrates and citric acid as a capping agent by an auto-combustion method followed by calcined at high temperature at 600ºC. The structural characteristics and single phase formation of the calcined sample is determined by X-ray diffraction (XRD). Magnetization measurements were obtained at room temperature by using a vibrating sample magnetometer (VSM), which showed that the calcined sample exhibited typical magnetic behaviour. © 2014 The Authors. Elsevier Ltd. All rights reserved. © 2015 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the conference committee members of the 4th International conference on Selection and peer-review under responsibility of the conference committee members of the 4th International conference on Materials Materials Processing and Characterization. Processing and Characterization. Keywords: Nano-crystalline Cobalt ferrite; Auto-combustion synthesis; XRD analysis; FTIR; VSM; SEM;
1. Introduction Recently metal–oxide nanoparticles have been the subject of much interest because of their unusual optical, electronic and magnetic properties, which often differ from the bulk. Cobalt ferrite, CoFe2O4, is a well-known spinel ferrite and magnetic material with high crystalline anisotropy, high coercivity, and moderate saturation magnetization. Nanocrystalline cobalt ferrites have been synthesized using a variety of physical methods, including mechanochemical
2214-7853 © 2015 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the conference committee members of the 4th International conference on Materials Processing and Characterization. doi:10.1016/j.matpr.2015.07.106
3606
T. Shanmugavel et al. / Materials Today: Proceedings 2 (2015) 3605 – 3609
[1], and thermal decomposition [2]. Wet chemical methods are particularly interesting for their versatility, lowtemperature preparation, and potential for production scale up. CoFe2O4 have been obtained by co-precipitation [3], hydrothermal [4], sol–gel [5], sonochemical [6], and micelle micro-emulsion [7] approaches. In all applications, the nanoparticle preparation method is of primary importance for the particle size distribution, shape, surface characteristics and magnetic properties. Cobalt nanocrystalline ferrites having wide applications in the field of electronic devices, ferrofluids, magnetic drug delivery, microwave devices, high-density information storage, catalysts and gas sensors [8-10]. Hence, they have been widely used in paint and coating systems [11]. Present work, we prepared CoFe2O4 using auto-combustion method, a simple, non-grinding, economic and versatile technique, which can be extended for large-scale production [12]. The prepared powder shows excellent magnetic properties and an average grain size of 35nm is produced in single step. 2. Experimental 2.1. Materials Iron nitrate(III) Fe(NO3)3·9 H2O, and cobalt nitrate(II) Co(NO3)2·6H2O, were purchased from Merck with purities exceeding 98.3%.Citric acid was purchased from Sigma Aldrich and was used without further purification. An appropriate amount of iron nitrate and cobalt nitrate were dissolved in to deionized water in the ratio (Fe:Co=2:1), then aqueous solution was continuously stirred by a magnetic stirrer. Chelating agent (citric acid) is added to produce the metal spinel ferrite with proposed ratio and it was added with nitrate aqueous solution until viscous resin was obtained. The resulting powder is calcined to high temperature 600ºc. 2.2. Characterization The characterization of the prepared cobalt ferrite nanoparticles was conducted by using various techniques to verify the particle size and distribution and to explore other parameters of interest. The structure of the CoFe 2O4 nanoparticles was characterized by the XRD technique using a Shimadzu diffractometer (model XRD 6000) using C u Kߙ (0.154 nm) radiation to generate diffraction patterns from the crystalline powder samples at ambient temperature over the 2 ߠ range from 10° to 80°. The Particle morphology was investigated by a Scanning Electron Microscope. Magnetic characterization of the cobalt ferrite nanoparticles was performed by using a vibrating sample magnetometer (VSM) (Lake Shore 4700) at room temperature with a maximum magnetic field of 10 kOe. 3. Result and Discussion Fig. 1 shows the powder XRD patterns of the CoFe2O4 obtained for calcined for 600°C. The characteristic peaks could be indexed for that cubic structure CoFe2O4, which is close agreement with the reported data (JCPDS File No. 03-0864). From that, it is known that the sample was pure CoFe2O4 crystals without impurity phases. Meanwhile, the reflection peaks become sharper and stronger with the increase of temperature. The peak broadening is purely due to the reduced particle size. The crystallite size of samples was determined from the broadening of cubic CoFe2O4 (311) X-ray spectral peaks using the Scherrer formula:[13] D = Kλ /β cos θ
[1]
4. where D is the crystallite size, λ the wavelength of the X-ray radiation, K usually taken as 0.89, and β is the line width at half maximum height, after subtraction of equipment broadening. Due to the annealing process results in a decrease in the defects, coalescence of crystallites, which in turns results in an increase in the average size of the nanoparticle [14].
3607
(311)
T. Shanmugavel et al. / Materials Today: Proceedings 2 (2015) 3605 – 3609
(440)
(511)
(422)
(400)
(222)
Intensity
(111)
(220)
Co600
JCPDS 03-0864
10
20
30
40
50
2 Theta
60
70
80
o
Fig.1. Powder X–ray diffraction patterns of (a) JCPDS 03-0864; (b) CoFe2O4 at 600 °C.
The morphology was examined by scanning electron microscopy (SEM) (Philips, XL30 EDAX model). Fig. 2 shows the FE-SEM image of CoFe2O4 nanoparticles. The structural morphology of the nanoparticles was investigated through FE-SEM[15]. It shows that the CoFe2O4 nanoparticle prepared by auto-combustion method have some agglomeration of the nanoparticle was observed. SEM images reveal that the samples’ surfaces exhibit welldefined crystalline nanoparticles of spherical shapes with soft agglomeration. The size of the particle, determined from the FESEM micrographs, is the order of 12–30nm. These values of particle size are in good agreement with the particle size calculated by Scherrer’s formula. Fig. 3 shows SEM micrographs of the powders.
Fig.2.FE-SEM for CoFe2O4 at 600 °C.
Fig.3.SEM for CoFe2O4 at 600 °C.
Fig. 4 shows the hysteresis loops of the samples calcined at 600°C. At room temperature, the sample exhibited hysteresis loop typical of magnetic behavior, indicating that the presence of an ordered magnetic structure can exist in the spinel system. It was known that the magnetic properties of nanosize particles depended on the preparation method and the particle size [16]. The values of saturation magnetization (Ms) of the samples at room temperature are 57 emu/g . The Ms value for CoFe2O4 sample is less than the value of saturation magnetization reported for bulk cobalt ferrite (80.8 emu/ g) [17]. While annealing generally decreases the lattice defects and strains, however, it can also cause coalescence of crystallites those results in increasing the average size of the nanoparticles. The magnetization sharply increases at low applied fields but at high field region it increases slowly and reach the saturation at l0 kOe magnetic field. As the temperature decreases, the coercivity values and saturation magnetizations of the samples increase. Due to the good ferromagnetic properties of samples, it is a capable material for high-density magnetic storage and medical diagnostics, etc.
3608
T. Shanmugavel et al. / Materials Today: Proceedings 2 (2015) 3605 – 3609
Co600
70 60 50
Momment (emu/gm)
40 30 20 10 0 -10
Ms= 56.71 emu/g Mr= 22.24 emu/g Hci= 1178.97 (Oe) Mr/Ms= 0.392
-20 -30 -40 -50 -60 -70 -10000
-5000
0
5000
10000
Field (Oe)
Fig. 4. VSM for CoFe2O4 at 600 °C.
4. Result and Discussion In conclusion, Nanocrystalline CoFe2O4 was synthesized by a low-temperature auto-combustion method utilizing only cobalt nitrate and iron nitrate as precursors, Citric acid as an agglomeration capping agent, and deionized water as a solvent. The modified citrate-gel method allows to mix the metal ions at atomic scale using stirring and to combine them through metal-citric gel network, leading to a perfect reaction between ions to form CoFe2O4. The X-ray diffraction analysis confirmed the cubic spinel phase formation and broadness of (3 1 1) indicates the smaller particle formation. The considerable broadening as well as the low intensity of all diffraction peaks indicate that the studied samples consist of quite small crystallites. There are no detectable traces of extra-crystalline phases. Scanning electron microscopy analysis reveals the highly agglomerated particles. This simple, cost-effective, and environmentally friendly method that produces no by-product effluents can be used to synthesize pure crystalline spinel cobalt ferrite nanoparticles. Furthermore, it can be extended to synthesizing other spinel ferrite nanoparticles of interest in nanotechnology. Acknowledgements One of the authors T. Shanmugavel wishes to thank to all the Management members and Department of Physics, and various department staff members of Excel Engineering College, Namakkal – 637 303, for providing a platform to perform the research. References [1] Y. Shi, J. Ding and H. Yin, 2000 , CoFe2O4 Nanoparticles Prepared by the Mechanical Method, Journal of Alloys and Compounds, Vol. 308, No. 1, pp. 290-295. [2] T. Hyeon, Y. Chung, J. Park, S.-S. Lee, Y.-W. Kim, B.H. Park, 2002, synthesis of high crystalline and monodisperse cobalt ferrite nanocrystals, J. Phys. Chem. B 106 6831–6833. [3] S. Komarneni, M.C. D’Arrigo, C. Leonelli, G.-C. Pellacani,1998, Microwave hydrothermal synthesis of nano ferrites. J. Am. Ceram. Soc. 81 ,3041–3043.
T. Shanmugavel et al. / Materials Today: Proceedings 2 (2015) 3605 – 3609
3609
[4] J.-G. Lee, J.-Y. Park, C.-S. Kim, 1998, Growth of ultra fine cobalt ferrite particles by their magnetic properties.,J. Mater. Sci. 33 ,3965– 3968. [5] J. de Vicente, A.V. Delgado, R.C. Plaza, J.D.G. Duran, F. Gonzalez- Caballero, 2000, Stability of cobalt ferrite colloidal particles. Effect of pH and applied magnetic fields,langmuir, 16(21), 7954-7961 . [6] M. Rajendran, R.C. Pullar, A.K. Bhattacharya, D. Das, S.N. Chintalapudi, C.K. Majumda,2001, , Magnetic properties of nanocrystalline CoFe2O4 powders prepared at room temperature: variation with crystallite size, J. Magn. Magn. Mater. 232 , 71–83. [7] S. Li, L. Liu, V.T. John, C.J. O’Connor, V.G. Harris,2001, Cobalt-ferrite nanoparticles: Correlations between synthesis procedures, structural characteristics and magnetic properties, IEEE Trans. Magn. 37 , 2350–2352. [8] F. Mazaleyrat, L.K. Varga, J. Magn. Magn. Mater. 215ˀ216 (2000) 253. [9] K. Yamaguchi, K. Matsumoto, T. Fujii, 1990, Magnetic anisotropy by ferromagnetic particles alignment in a magnetic field, J.Appl. Phys. 67 4493ˀ4495. [10] Y. Shahoo, A. Goodarzi, M.T. Swihart, J. Phys. Chem. B 109 (2005) 3879ˀ3885. [11] Z. Aixiang, X. Weihao, X. Jian, 2005, Electroless Ni–P coating of cenospheres using silver nitrate activator,Surf. Coat. Technol. 197 142ˀ 147. [12] J. F. Crider, Ceram. Eng. Sci. Proc. 3 (1982) 519. [13] H.G. Jiang, M. Rühle, E.J. Lavernia, J. Mater. Res. 14 (1999) 549. [14] T.P. Raming, A.J.A. Winnubst, C.M. van Kats, P. Philips, J. Colloid Interface Sci. 249 (2002) 346. [15] Manish Srivastava, S. Chaubey, Animesh K. Ojha, Investigation on size dependent structural and magnetic behavior of nickel ferrite nanoparticles prepared by sol–gel and hydrothermal methods, Materials Chemistry and Physics 118 (2009) 174–180. [16] Y. Ahn, E.J. Choi, S. Kim, H.N. Ok, Magnetization andM¨ossbauer study of cobalt ferrite particles from nanophase cobalt iron carbonate, Mater. Lett. 50 (2001) 47–52. [17] D.J. Craik, Magnetic Oxides, Part II, Wiley, London, 1975, p. 703.