Bhavikatti Ijest 2010 02

A.M.Bhavikatti et. al. / International Journal of Engineering Science and Technology Vol. 2(11), 2010, 6532-6539

CHARACTERIZATION AND ELECTROMAGNETIC STUDIES OF

NANO-SIZED BARIUM FERRITE

A.M.BHAVIKATTI*

Rural Engineering College, Bhalki585328, INDIA

DR.SUBHASH KULKARNI

Jaypraksh Narayan College of Engineering, Mahaboobnagar - 509001, INDIA

DR. ARUNKUMAR. LAGASHETTY

Appa Institute of Engineering and Technology, Gulbarga 580102, INDIA.

Abstract The present article reports some of the interesting and important electromagnetic and impedance studies of nanostructured barium ferrite. Here, the nano-sized barium ferrite (BaFe2O4) was synthesized by using microwave route. The sample was characterized by X-ray diffraction, SEM and IR studies. Electrical resistance(R) measurements of the sample revealed a very high resistivity and the results indicated a fall in resistivity with the rise in temperature. The obtained dc conductivity is found to be very low of the order of 10-8 S/cm .The dc conductivity follows the Arrhenius law. The hysteresis M-H loops for this sample was traced using the Vibrating Sample Magnetometer (VSM) to study the parameters coercivity (Hc), saturation magnetization (Ms) , remanence (Mr) and squareness ratio( SQR). The complex impedance spectroscopy (CIS) technique was used to study the electrical response of the nanostructured sample in a wide range of frequencies (1 KHz to 1MHz) at different temperatures (07000 C). Key words: Microwave synthesis, nano-sized barium ferrite, resistivity, conductivity, impedance studies 1. Introduction Ferrites have continued to attract attention over the years. As magnetic materials, ferrites cannot be replaced by any other magnetic material because they are relatively inexpensive, stable and have a wide range of technological applications in transformer core, high quality filters, high and very high frequency circuits and operating devices. The physical properties of ferrites are controlled by the preparation conditions, chemical composition, sintering temperature and time, type and amount of substitutions [1]. In recent years, nanostructured materials have drawn outstanding attention due to the unique mechanical, electrical, optical, and magnetic properties. The unique properties of nanostructured materials are due to their changed electronic structure, close to that of an isolated atom or molecule. Among the nanoscale inorganic materials, the magnetic metal oxides and their composites are of particular interest due to their exciting applications in the areas of quantum computing, information storage media, magnetic resonance imaging, sensors, refrigeration, electromagnetic wave absorption and modulation [2]. Recent studies have shown that, physical properties of nano particles are influenced significantly by the processing techniques .Since crystalline size, distribution of particle sizes and inter particle spacing have the greatest impact on magnetic particles, the ideal synthesis techniques must provide superior control over these parameters .A variety of techniques have been employed for the synthesis of nano particles with definite shapes and sizes [3]. Nanocrystalline barium ferrites are very interesting because of its chemical properties and thermal studies [4]. These materials are technologically important and have been used in many applications such as magnetic recording media [5]. Recently, nanocrystalline magnetic materials have been receiving more and more attention due to their novel material properties, which are significantly different from those of their bulk counterparts [6].

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Microwave firing of ceramics is a technology that has attracted much scientific interest as a technology for ceramic manufacturing [7-9]. Microwave firing could be an interesting firing technology for crystalline magnetic ceramics, such as barium ferrite, for the following reasons,

Microwave firing can be considered as direct heating method and is therefore expected to be more economic. The energy consumption should be reduced because the ferrite materials are heated directly and less energy is wasted to heat the kiln.

Higher densities are desired for all magnetic properties such as saturation magnetization, magnetic permeability, etc

Microwave firing allows the achievement of high heating rates that cannot be achieved by conventional furnaces and this may lead to significant reduction of the firing cycles times.

Earlier, we have presented the microwave synthesis of nano-sized barium ferrite [10].Recently, we have presented electrical studies of nano sized barium ferrite [11].In the present article, we investigate the dc conductivity, resistivity, magnetic properties, real and imaginary part of impedance of the nano-sized barium ferrite. Barium ferrite, which is a well-known ferric-magnetic material with superior chemical stability and anti-erosion properties, attracted extensive attention in recent years .Owing to its high anisotropy property; this material has been widely used in the fabrication of magnetic and magneto-optic devices. Applications are also found in microwave devices mainly because of its high resistivity and permittivity at high frequency [12] 2. Experimental Procedure

2.1.1 Materials and Methods

Barium chloride, ferrous ammonium sulphate, oxalic acid and urea used were AR grade. Microwave method is used for the synthesis of barium ferrite materials using urea as a fuel for the combustion reaction.

2.1.2 Preparation of pellet

The powders were crushed and ground finally to reduce it to small crystallites of uniform size. The mixture was dried and a small amount of PVA binder was added to the powder .The resulting powders were pressed by applying a pressure of 70Mpa in a stainless steel die to make pellets of 1cm diameter and 1cm thickness. The pellet samples were well polished to remove any roughness present on the surface of pellets. .For the dielectric and conductivity measurements; silver paint was applied on the polished surfaces of the pellets and air-dried to have good ohmic contacts. The binder burn off was carried out by a slow heating rate and soaking time being an hour.

2.1.3 Instrumentation

D c conductivity measurements were carried out with Keithly 2010 electrometer using two probe methods. The resistance R was measured for different temperatures and the conductivity was calculated. The impedance spectroscopy was carried out to find the variation of real and imaginary part of impedance with temperature at different frequencies using HP-4192A Impedance analyzer.

2.1.2 Synthesis of nanosized BaFe2O4

Barium oxalate and iron oxalate precursors was prepared by dissolving equimolar quantities of barium chloride and ferrous ammonium sulphate with oxalic acid and was stirred well in a separate beakers. The precipitates of barium and iron oxalate obtained was filtered through sintered glass crucible and was washed with distilled water till free from chloride ions and oxalic acid, finally with dry acetone and was then dried under vacuum. The barium oxalate, iron oxalate and urea were mixed in weight ratio 1:1:5 and ground well in a pestle and mortar. Resultant solid was placed in a crucible and ignited in microwave oven. The reaction was found to be completed in about ten minutes at high power level and forms a brown crystalline BaFe2O4 material. On cooling to room temperature no trace of carbon impurities was observed in the final residue of nano-sized barium ferrite.

2.2Characterization:

The powder X-ray diffraction pattern was obtained from GEOL JDX-8P or SEIMEN (Japan) X-ray diffractometer using CuK radiation. The morphology of the maghemite sample was obtained from Leica Cambridge-440 scanning electron microscopy. Bonding in as prepared nano-sized barium ferrite was obtained from Perkin-Elmer FTIR spectrophotometer (Model-1000).

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3 Results and Discussion

3.1X-ray diffraction

Table-1 shows observed 2 values as well as literature 2 values of the as prepared barium ferrite obtained from XRD tool. This table also shows the indexing of the XRD peaks of the prepared sample. Observation of literature 2 values and observed 2 shows the formation of BaFe2O4 sample. Unit cell parameters were obtained by least square refinement of the powder XRD data. The lattice parameters are in agreement with the data reported in literature (JCPDS-46-0113). The color of the as synthesized barium ferrite is brown which is similar to the one which is mentioned in the literature. The average crystalline size was found to be about 74nm and was calculated using equation (1). The Average grain size has been calculated using Debye Scherrers equation (1) as shown below D = 0.9 / 1/2 cos -------------------- (1)

Where = wave length of the x- ray beam 1/2 = Angular width at the half max intensity = Braggs angle

Table-1

Indexed XRD data of BaFe2O4 sample

Hkl 2obs 2lit Iobs 402 28.240 28.235 60

212 28.435 28.428 100

610 32.720 32.716 50

020 33.269 33.266 30

802 43.610 43.604 10

422 44.172 44.164 23

2obs = Observed 2 values, 2lit = literature 2 values Iobs = Observed intensity

Table-2 Vibrational Frequencies of BaFe2O4 sample

Peak No. Vibrational

Frequencies (cm-1|) 1 3100 2 1075 3 530 4 475 5 445 6 440 7 250 8 230 9 210

10 200 3.2 Scanning Electron Micrograph

Figure-1 shows SEM image of as prepared barium ferrite sample. The particles are irregular in shape with compact arrangement. In some particles flakes of agglomerates are also observed. Needle shaped particles forms globular arrangement with self assembled blocks.

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- 5 0 0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0 4 0 0- 2 .0 0 E + 0 0 8

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Figure-1: SEM image of as BaFe2O4 sample

3.3Infrared studies The infrared study was performed aiming to ascertain the metal-oxygen and metal-metal bond in the prepared ferrite sample. Table-2 gives the vibrational frequencies of the as synthesized BaFe2O4. The ferrite sample shows the absorption in the region 3100, 1075, 530, 475, 445, 440, 250, 230, 210 and 200 cm-1. The peak at 3100 cm-1 corresponds to water of adsorption and the peak at1075cm-1 is due to the presence of some overtones. The peaks at 530, 475, 445 and 440cm-1 correspond to the metal-oxygen vibrational modes of the spinel compound [13]. The peaks at around 250, 230, 210 and 200cm-1 is observed is due to metal-metal (Ba-Fe) vibration frequency range. This confirms the formation of BaFe2O4.

3.4 Resistivity

High dc resistivity of 1.75 109 Ohm-cm is obtained at room temperature and it decreases with increase of temperature according to the Arrhenius equation. Increasing temperature leads to decrease in resistivity, which is the normal behavior of semiconducting material. Increase in temperature of the sample will help the trapped charges to be liberated and participate in the conduction process, with the result of decreasing the resistivity. This decrease in resistivity could be related to the increase in the drift mobility of the thermally activated electrons according to the hopping conduction mechanism and not to thermally creation of the charge carriers. [14].

Figure-2: Resistivity of BaFe2O4 sample

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0 50 100 150 200 250 300 350 400 450

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3.5 DC Conductivity

DC conductivity increases with increasing temperature indicating a semiconducting behavior. The conductivity obtained here is very less and the maximum conductivity obtained here is 410-8 S/cm at a temperature of 4000 C. The temperature variation of conductivity in this sample studied in the present work confirm to the Arrhenius law [15] as shown in equation (2),

0 exp(- Edc /KT) -------(2) Where, Edc activation energy required for the hopping process.

Figure-3: Conductivity of BaFe2O4 sample

3.6 Magnetic studies

The hysteresis loop gives the relation between the magnetization M and the applied field H. The parameters extracted from the hysteresis loop that are most often used to characterize the magnetic properties of magnetic media include; the saturation magnetization Ms, the remanence Mr, the coercivity Hc, the squareness ratio SQR, which is related to the slope at Hc .The squareness ratio is given by the ratio of (Mr/Ms) and is essentially a measure of how square the hysteresis loop is. In general large SQR values are desired for recording medium [16]. Magnetic parameters were determined for the sample by using a vibrating sample magnetometer at room temperature at a maximum applied field of 81 KOe. Saturation magnetization, remanence magnetization and coercivity were determined from the hysteresis loop and were found to be21.59 emu/gm, 4.55emu/gm and 438.02 Oe, respectively. The squareness ratio is found to be very low i.e.0.2107.Values for both coercivity and saturation magnetization are found to be lower when as compared to reported bulk values. This could be due to presence of minor amounts of phases other than barium ferrite.

The hysteresis curves are used to check the difference between the soft magnetic materials and the hard magnetic materials. For a hard magnetic material, the area inside the hysteresis loop should be large because it represents the amount of useful magnetic energy that can be made available to do work. But for a soft magnetic material, it represents undesirable core loss .Materials having properties between hard and soft materials are referred to as semi-hard magnetic materials.

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Figure-4: M-H Hysteresis curve of BaFe2O4 sample

3.7. Impedance studies The complex impedance spectroscopy (CIS) technique was used to analyze the electrical response of the sample in a wide range of frequencies (1 KHz to 1MHz) at different temperatures (07000 C). The dielectrical properties of a material are often represented in terms of complex dielectric permittivity *, complex impedance Z* and electric modulus M*, which are related to each other as: Z*=Z jZ; M*=1/*() = j(C0)Z*=M + jM, where (Z,M) and (Z,M) are the real and imaginary components of impedance and modulus, respectively, j = -1 the imaginary factor and is the angular frequency, = 2f[1]. Due to the large amount of results obtained (five types of samples), we present the results associated only to the present sample, and however, we claim that the results obtained in all the remaining four samples have similar behavior [17].

(a) (b) (c) (d) Fig (5) Variation of real part of impedance (Z) with temperature at four different frequencies(a) 1KHz (b) 10KHz (c) 100KHz and (d) 1MHz

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3.7.1. Variation of real part of impedance (Z)- The variation of real part of impedance (Z) at selected temperatures and different frequencies is shown in Figs (5). It indicates that the real part of impedance (i.e., resistance) decreases with the rise in frequency and temperature. A decrease in Z with the rise in frequency indicates a possibility of increase in the ac conductivity with the increase in frequency [1].The maximum Z value obtained is 3.5106 Ohms at a frequency of 1 KHz and a temperature of 3500 C. The minimum value of Z obtained is 450 Ohms at 1MHz frequency and a temperature of 500C. Due to the large amount of results obtained (five types of samples are under investigation), we present the results associated only to the present sample, and however, we claim that the results obtained in all the remaining four samples have similar behavior [17]. (a) (b) (c) (d) Fig (6) Variation of imaginary part of impedance (Z) with temperature at four different frequencies(a) 1KHz (b) 10KHz (c) 100KHz and (d) 1MHz

3.7.2. Variation of imaginary part of impedance (Z) Fig (6) represents the variation of imaginary part of impedance (Z) with different temperatures at different frequencies. This plot is suitable for evaluation of the relaxation frequency of the most resistive component. The loss spectrum has some important features: (a) the appearance of two peaks. (b) the value of (Z) decreases and shifts to the higher frequency side as temperature increases, (c) the first peak, typical peak broadening and the second peak, typical peak symmetric and a decrease in the height of the peaks with increasing temperature[1]. 4. Conclusions

In summary, we have successfully synthesized nanostructured barium ferrite by using microwave synthesis. Microwave route for metal oxide materials is very simple, energy efficient technique and easy to scale up. Urea is used as a fuel for the reaction and this fuel can be used for synthesis of other oxide materials. Temperature dependent DC resistivity decreases with increase in temperature ensuring the semiconductor like nature of the nanostructured sample.High value of dc resistivity, of the order of 109 cm, makes this ferrite suitable for the

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high frequency applications where eddy current losses are significant. The observation of magnetic hysteresis loop at room temperature confirms existence of magnetic ordering at room temperature in this sample. Acknowledgements The authors are thankful to Prof. A Venkataraman, Department of Materials Science, Gulbarga University, Gulbarga for helping in XRD analysis. Authors acknowledge Dr. Shashidhar Reddy, IISc,, Bangalore for providing XRD pattern and SEM images .One of the authors(AMB) would like to thank, Dr.B.B.Lal, principal REC Bhalki for his constant encouragement.

5. References [1] M.M. Costa, G.F.M. Pires Junior, A.S.B. Sombra, Dielectric and impedance properties Studies of the lead doped (PbO)-Co2Y type

hexaferrite (Ba2Co2Fe12O22 (Co2Y)), International Journal of Materials Chemistry and Physics, 123, pp 3539, 2010. [2] Manish Srivastavaa, Animesh K. Ojha, S. Chaubey, Prashant K. Sharma, Avinash C. Pandey, Influence of calcinations temperature

on physical properties of the nanocomposites containing spinel and CuO phases ,Journal of Alloys and Compounds 494,pp 275284,2010.

[3] D.Bahadur, S.Rajkumar, Ankit kumar, Influence of Fuel ratios on auto combustion synthesis of barium ferrite nano particles, Intl.J.Chem .Sci.,Vol, 118, No 1,pp15,2006.

[4] S. Maensiri, C. Masingboon, B. Boonchom and S. seraphin, Scipt. Mater,.56 , pp797, 2007. [5] M. Sugimoto, J.Am. Ceram. Soc. 1999, 82, 269. [6] A Lagashetty, S. Kalyani and S.Omprakash. J.Mater. Sci. Res. Ind. 2005, 3(2), 145 [7] Harish Bhat, M., Chakravarthy, B P., Ramakrishnan, P. A., Levasseur, A., and Rao, K. J., Bull. Mater. Sci, 23(6), 461, (2000). [8] Ramesh, P. D., and Rao, K. J., Adv. Mater. 7,177, (1995) [9] A. Lagashetty, V. Havanoor, S. Basavaraja, S. D. Balaji and A. venkataraman. Sci. & Tech. Adv. Mater. , 2008. [10] A.M.Bhavikatti ,Subhash.kulkarni, Arunkumar.Lagashetty, Microwave synthesis of Nano sized Barium Ferrite, at 2nd International

Symposium on advanced materials and Polymers for aerospace and defence applications.(SAMPADA-2008 ) at University of Pune, on DEC-08th to 12th, 2008

[11] A.M.Bhavikatti ,Subhash.kulkarni, Arunkumar.Lagashetty, Electrical studies of Nano-sized Barium ferrite, International Journal of Materials Science, ISSN 0973-4589, Volume 4, No4, pp485-492, 2009.

[12] Wen-Tsang Liu , Jyh-Fu Lee , Jenn-Ming Wu , X-ray absorption spectroscopic study of barium ferrite thin films synthesized by solgel method, Materials Chemistry and Physics, 69 ,pp8994,2001

[13] C. N .R. Rao, Chemical applications of infrared spectoscopy, Academic Press, New York and London 1963. [14] J.Chand, M.Singh, Electric and dielectric properties of Mg Gd0.1Fe1.9O4 ferrite, Journal of Alloys & Compounds, 2009-Article in

press [15] N.R.Reddy, M.Venkataramana, K.Krishnaveni, K.V.Shivakumar, V.R.K.Murthy, Dielectric, elastic, anelastic and conductivity

behavior of ferromagnetic composites Ni0.5Zn0.5Fe1.95O4- +Ba0.8Pb0.2TiO3, Bull. Mater .Sci. Vol.30, No4,pp 357-363,2007. [16] B. C. Dodrill, Magnetic Media Measurements with a VSM, Lake Shore Cryotronics, Ohio. [17] A.M.Bhavikatti, Subhash kulkarni, Arunkumar Lagashetty, Impedance Spectroscopy and dc studies of Nano-sized Magnesium

ferrite, International Journal of Materials Science, ISSN 0973-4589, Volume 5, Number 3, pp 351-359, 2010.

Biographies of authors

A M Bhavikatti received a degree in Electronics & communication in 1985, has completed ME in power electronics in 1991 and is a research scholar in Electronic materials .Till date, he has more than 35 publications in International and National journals and Conferences .Presently he is a Professor and Head of Electronics and Communication Engineering Dept at Rural Engineering College, Bhalki, Karnataka state

Dr.Subhash.S.Kulkarni completed BE in Electronics and Communication Engg in 1988 and Masters program in Electronic Design & Technology from Indian Institute of Science, Bangalore in 1995.He was awarded PhD from IIT, Kharagpur in 2002 in the area Geometric Deformable Models for Image Segmentation .Presently he is working as Principal in Jayaprakash Narayan College of Engineering, Mahabubnagar, Andhra Pradesh. Till date he has more than 30 publications in International & National journals and Conferences and is guiding 8 research scholars.

Dr.Arunkumar.Lagashetty completed M.Sc in 2000 and M.phil in 2001 from Gulbarga University, Gulbarga. He was awarded PhD from Gulbarga University in 2004 in the area of Physical chemistry .He was a Junior Research fellow for an UGC Project. Till date he has more than 28 publications in International and National journals and more than 30 publications in conferences. Presently, he is working as a Head of department of Chemistry at Appa Institute of Engineering and Technology, Gulbarga, Karnataka state.

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