World Journal of Condensed Matter Physics
Vol.1 No.3(2011), Article ID:6934,4 pages DOI:10.4236/wjcmp.2011.13016

Structural and Magnetic Properties of BaCoxFe12-xO19 (x = 0.2, 0.4, 0.6, &1.0) Nanoferrites Synthesized via Citrate Sol-Gel Method

Sonal Singhal*, Kirandish Kaur, Sheenu Jauhar, Santosh Bhukal, S. Bansal


Department of Chemistry, Panjab University, Chandigarh, India.

Email: *

Received May 4th, 2011; revised May 26th, 2011; accepted June 10th, 2011.

Keywords: Barium Ferrite, Magnetic Moment, Coercivity, XRD


Cobalt substituted barium ferrites, BaCoxFe12-xO19 (x = 0.2, 0.4, 0.6 & 1.0) have been synthesized via citrate sol-gel method. All the samples have been annealed at 1000℃ and characterized using Fourier Transform Infra Red spectroscopy, X-Ray Diffractography and Vibrating Sample Magnetometry. The FT-IR spectra of the samples exhibit two frequency bands in the range of 580 cm1 and 460 cm1, corresponding to the formation of metal oxides. The XRD studies reveal a crystallite size of ~55 nm. The saturation magnetization decreases from 96.3 emu/g to 47.8 emu/g with increasing concentration of cobalt due to the lower magnetic moment of Co2+ (3 µB) as compared to Fe3+ (5 µB). The coercivity values also show a decreasing behaviour from 3800 Oe to 1750 Oe with increasing cobalt concentration due to reduced magnetocrystalline anisotropy.

1. Introduction

M-type Barium hexaferrites are magnetically hard materials that possess versatile properties like high saturation magnetization, high coercivity, large uniaxial anisotropy and excellent chemical and magnetic stability. These properties make them well suited materials for numerous applications. They have been extensively used in permanent magnets, high density recording media and magneto optical recording technologies [1-4]. In addition, they are suitable microwave absorbing materials due to a significant permeability value (>1) [5].

BaFe12O19 has a magnetoplumbite structure and its unit cell is a combination of two structural blocks aligned in the direction of hexagonal c-axis: RSR*S*. In R block, the lattice is made of O2 ions, forming a hexagonal closed packed structure, with iron ions occupying the tetrahedral, octahedral and bipyramidal sites. However, in S block, O2 ions form a cubic closed packed lattice and iron ions occupy the tetrahedral and octahedral sites [6]. It is well known that their structural and magnetic properties are closely connected to the distribution of Fe ions among various interstitial sites, and it has been found that these properties can be changed by doping of Fe3+ and Ba2+ with different types of cations and cation combinations. Due to this, researchers have a lot of interest in modifying structural, magnetic and electrical properties of nanoferrites, according to the requirement for various practical applications by different cation substitutions and by using different synthetic routes under varying conditions [7-11]. Sandaranarayanan et al. [7] studied the effect of annealing temperature on Barium ferrites and reported that their crystallization begins around 550℃ and fully crystalline phase is obtained in the range of 700℃ - 900℃. Mendoza-Suarez et al. [8] synthesized Zn-Sn doped Ba ferrites, BaFe12-2xZnxSnxO19, using ball milling method and found that the coercivity decreases due to reduction of the magnetocrystalline anisotropy. The saturation magnetization has also been reported to decrease with increase in Zn-Sn concentration. Kresisel et al. [9] reported that with increasing concentration of Co-Ti dopants in barium ferrites, axial anisotropy reduced and further changed to nearly planar magnetic anisotropy. Teh et al. [10] synthesized Co2+ and Co3+ substituted Ba ferrites via sol-gel method and found that Co2+ doping decreases the value of coercivity and saturation magnetisation significantly. However, Co3+ doping shows less change in magnetic properties. Ghasemi et al. [11] prepared Mn-Co-Zr substituted Ba ferrites and studied that substitution of these cations is very effective in reduction of coercivity at low level of substitution.

The present work deals with the formation of nanoferrites of cobalt substituted M-type barium ferrites via citrate sol-gel method. Their characterisation has been done by Fourrier Transform Infrared (FT-IR) spectroscopy, powder X-Ray Diffraction (XRD) studies and Vibrating Sample Magnetometry (VSM). The effect of increasing Co2+ concentration on the magnetic properties has also been studied.

2. Experimental

2.1. Synthesis

BaCoxFe12-xO19 (x = 0.2, 0.4, 0.6, 0.8 & 1.0) were synthesized using the citrate sol-gel method [12,13]. AR grade Ba(NO3)2, Fe (NO3)3·9H2O, Co(NO3)2·6H2O and citric acid were weighed in appropriate stoichiometric proportions and dissolved in minimum amount of distilled water at 80℃. Ethylene glycol was added as gelling agent. Then, all the dissolved solutions were mixed with continued stirring and a homogenous mixture was obtained. The resulting solution was then heated at 10℃ and stirred using a hot plate magnetic stirrer that resulted in gel formation. Thermal decomposition was carried out and the ferrite powder was obtained, which was annealed at 1000℃ for 2 hours in muffle furnace.

2.2. Physical measurements

Fourier Transform infra red (FT-IR) spectra have been recorded using Perkin Elmer RX-1 FT-IR spectrophotometer with KBr pellets in the range 4000 - 400 cm–1. Powder X-ray diffraction (XRD) studies have been carried out using a Bruker AXS, D8 Advance spectrophotometer with Cu-Kα radiation Hitachi (H-7500). The magnetic properties have been measured at room temperature by a Vibrating Sample Magnetometer (VSM) (155, PAR) up to a magnetic field of ±10 kOe.

3. Results and Discussion

3.1. FT-IR Measurements

The FT-IR spectra of all the ferrite compositions have been recorded in the range of 4000 - 400 cm–1, using KBr plates. In the low frequency range, the spectra show two main peaks corresponding to the vibrational modes of metal oxide of ferrites that are interpreted in the light of literature study of absorption region of ferrite [14]. The peak observed in the range of 580 cm–1 is attributed to the stretching vibration of tetrahedral group. However, the peak in the range of 460 cm–1 is due to stretching vibration of octahedral group.

3.2. X-Ray Diffraction Studies

The powder X-Ray diffractographs for all the as obtained as well as annealed samples have been recorded and are shown in Figure 1. The XRD patterns of the ferrite samples show characteristic diffraction peaks corresponding to the M-type barium ferrite structure, having point group P63/mmc, indicating that the crystal structure does not transform and remains hexagonal magnetoplumbite after substitution with cobalt ions. The average crystallite size for each composition has been calculated from the line broadening of the most intense peak corresponding to (1,1,4) plane of magnetoplumbite structure according to Scherrer equation [15] given below

D = kλ/βcosθ

where D is the average size of the crystallites, k is the scherrer constant, λ is the wavelength of radiation (1.5405 Å), β is the peak width at half height or full width half maximum. The values of crystallite size are listed in Table 1 and the average crystallite size is found to be ~55 nm.

The lattice parameters, a and c, have been calculated using Powley as well as Le-Bail refinement methods (built in TOPAS V2.1 of BRUKER AXS), and are listed in Table 1. It is observed that the lattice parameters remain constant on increasing Co2+ concentration.

3.3. Magnetic Properties

The room temperature magnetic hysteresis loops for all the as obtained as well as annealed samples have been recorded. Typical loops for all the annealed ferrite samples are shown in Figure 2. From these plots, saturation magnetization (Ms), coercivity (Hc) and squareness ratio (Sq) have been calculated and are given in Table 1. From Table 1, it is seen that the saturation magnetization decreases as the Co2+ concentration is increased. This is

Figure 1. X-Ray diffractographs of (a) BaCo0.2Fe11.8O19; (b) BaCo0.4Fe11.6O19; (c) BaCo0.6Fe11.4O19; (d) BaCo0.8Fe11.2O19; (e) BaCo1.0Fe11O19 annealed at 1000℃.

Table 1. Crystallite size, D (nm); Lattice parameter (a); Saturation Magnetisation (Ms), Coercivity (Hc) and Squareness Ratio (Sq) of the ferrites annealed at 1000℃.

Figure 2. Hysteresis loops of BaCoxFe12-xO19 (x = 0.0, 0.2, 0.4, 0.6, 1.0) annealed at 1000℃.

attributed to the lesser magnetic moment of Co2+ ions (3 µB) as compared to Fe3+ ions(5 µB) and their substitution in 12k and 2a sites of the lattice, in preference to the 4f2 sites. The coercivity value decreases from 5200 to 1750 Oe with increasing cobalt concentration (x = 0.0 to 1.0) due to reduction in magnetocrystalline anisotropy [16,17].

The value of squareness ratio has been calculated by formula

Sq = Mr/Ms

where Mr is the remnance and Ms is the saturation magnetisation. From Table 1, it is observed that the squareness ratio increases with increase in cobalt ion concentration.

4. Conclusions

Cobalt substituted barium ferrites BaCoxFe12-xO19 (0.2, 0.4, 0.6 & 1.0) were synthesized using citrate sol-gel method. The formation of M-type ferrites has been confirmed by FT-IR and XRD characterization. The crystallite size is found to be ~55 nm. The values of saturation magnetization and coercivity decrease with increasing cobalt substitution due to less magnetic moment of Co2+ ions as compare to Fe3+ ions and reduced magnetocrystalline anisotropy respectively.

5. Acknowledgements

Grateful thanks to the UGC for the financial support for this research work under the scheme of UGC-major project.


  1. M. Koleva, P. Atanasov, R. Tomov, O. Vankov, C. Matin, C. Ristoscu, I. Mihailescu, D. Iorgov, S. Angelova, C. Ghelev and N. Mihailov, “Pulsed Laser Deposition of Barium Hexaferrite (BaFe12O19) Thin Films,” Applied Surface Science, Vol. 154-155, 2000, pp. 485-491. doi:10.1016/S0169-4332(99)00404-3
  2. H. Sözeri, İ. Küçük and H. Özkan, “Improvement in Magnetic Properties of La Substituted BaFe12O19 Particles Prepared with an Unusually Low Fe/Ba Molar Ratio,” Journal of Magnetism and Magnetic Materials, Vol. 323, No. 13, 2011, pp. 1799-1804. doi:10.1016/j.jmmm.2011.02.012
  3. R. Carey, P. A. Gago-Sandval, D. M. Newman and B. W. J. Thomas, “The Magnetic and Magneto-Optical Properties of Co, Cr, Mn, and Ni Substituted Barium Ferrite Films,” Journal of Applied Physics, Vol. 75, No. 10, 1994, pp. 6789-6791. doi:10.1063/1.356831
  4. T. Yamauchi, Y. Tsukahara, T. Sakata, H. Mori, T. Chikata, S. Katoh and Y. Wada, “Barium Ferrite Powders Prepared by Microwave-Induced Hydrothermal Reaction and Magnetic Property,” Journal of Magnetism and Magnetic Materials, Vol. 321, No. 1, 2009, pp. 8-11. doi:10.1016/j.jmmm.2008.07.005
  5. X. Ping, H. Xijiang and M. Wang, “Synthesis and Magnetic Properties of BaFe12O19 Hexaferrite Nanoparticles by a Reverse Microemulsion Technique,” The Journal of Physical Chemistry C, Vol. 111, No. 16, 2007, pp. 5866- 5870. doi:10.1021/jp068955c
  6. D. Lisjak, K. Bobzin, K. Richardt, M. Begard, G. Bolelli, L. Lusvarghi, A. Hujanen, P. Lintunen, M. Pasquale, E. Olivetti, M. Drofenik and T. Schlafer, “Preparation of Barium Hexaferrite Coatings Using Atmospheric Plasma Spraying,” Journal of the European Ceramic Society, Vol. 29, No. 11, 2009, pp. 2333-2341. doi:10.1016/j.jeurceramsoc.2009.01.028
  7. V. K. Sandaranarayanan and D. C. Khan, “Mechanism of the Formation of Nanoscale M-Type Barium Hexaferrite in the Citrate Precursor Method,” Journal of Magnetism and Magnetic Materials, Vol. 153, No. 2, 1996, pp. 337- 346. doi:10.1016/0304-8853(95)00537-4
  8. G. Mendoza-Suarez, K. K. Johal, H. Mancha-Mohinar, J. I. Escalante-Garcia and M. M. Cisneros-Guerrero, “Magnetic Properties of Zn-Sn-Substituted Ba-Ferrite Powders Prepared by Ball Milling,” Materials Research Bulletin, Vol. 36, No. 15, 2001, pp. 2597-2603. doi:10.1016/S0025-5408(01)00751-6
  9. J. Kresisel, H. Vincent, F. Tasset, M. Pate and J. P. Ganne, “An Investigation of the Magnetic Anisotropy Change in BaFe12−2xTixCoxO19 Single Crystals,” Journal of Magnetism and Magnetic Materials, Vol. 224, No. 1, 2001, pp. 17-29. doi:10.1016/S0304-8853(00)01355-X
  10. G. B. Teh, S. Nagalingam and D. A. Jefferson, “Preparation and Studies of Co(II) and Co(III)-Substituted Barium Ferrite Prepared by Sol-Gel Method,” Materials Chemistry and Physics, Vol. 101, No. 1, 2007, pp. 158-162. doi:10.1016/j.matchemphys.2006.03.008
  11. A. Ghasemi and A. Morisako, “Static and High Frequency Magnetic Properties of Mn-Co-Zr Substituted Ba-Ferrite,” Journal of Alloys and Compounds, Vol. 456, No. 1-2, 2008, pp. 485-491. doi:10.1016/j.jallcom.2007.02.101
  12. X. F. Yang, Q. L. Li, J. X. Zhao, B. D. Li and Y. F. Wang, “Preparation and Magnetic Properties of Controllable-Morphologies Nano-SrFe12O19 Particles Prepared by Sol-Gel Self-Propagation Synthesis,” Journal of Alloys and Compounds, Vol. 475, No. 1-2, 2009, pp. 312-331. doi:10.1016/j.jallcom.2008.08.019
  13. L. A. Garc´ıa-Cerda, O. S. Rodr´ıguez-Fernández, and P. J. Reséndiz-Hernández, “Study of SrFe12O19 Synthesized by the Sol-Gel Method,” Journal of Alloys and Compounds, Vol. 369, No. 1-2, 2004, pp. 182-184. doi:10.1016/j.jallcom.2003.09.099
  14. M. J. Iqbal and Barket-ul-Ain, “Synthesis and Study of Physical Properties of Zr4+-Co2+ Co-doped Barium Hexagonal Ferrites,” Materials Science and Engineering B, Vol. 164, No. 1, 2009, pp. 6-11.
  15. B. D. Cullity, “Elements of X-Ray Diffraction,” Addison-Wesly Publishing, Boston, 1976.
  16. M. Kishimoto, S. Kitahata and M. Amemiya, “Effect of Magnetic Anisotropy of Ba-Ferrite Particles on Squareness of Perpendicular Recording Media,” Journal of Applied Physics, Vol. 61, No. 8, 1987, pp. 3875-3877. doi:10.1063/1.338626
  17. G. Mendoza-Suarez, L. P. Rivas-Vazquez, J. C. Corral-Huacuz, A. F. Fuentes and J. I. Escalante-Garcia, “Magnetic Properties and Microstructure of BaFe11.6−2x- TixMxO19 (M = Co, Zn, Sn) Compounds,” Physica B: Condensed Matter, Vol. 339, No. 2-3, 2003, pp. 110-118.