Studies on Mn(1-x)ZnxFe2O4 Nanoparticles Synthesized by Co-Precipitation Method

8/3/2019 Studies on Mn(1-x)ZnxFe2O4 Nanoparticles Synthesized by Co-Precipitation Method

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International Journal of Nanotechnology and ApplicationsISSN 0973-631X Volume 4, Number 1 (2010), pp. 51-59 Research India Publicationshttp://www.ripublication.com/ijna.htm

Studies on Mn (1-x) ZnxFe2O4 Nanoparticles

Synthesized by Co-Precipitation Method

D. Santhosh Kumar1* and K. Chandra Mouli

2

1Solid State Physics & Materials Science Research Laboratories, Dept. of Physics,

Andhra University, Visakhapatnam-530003, India.* Email: [email protected]. of Eng. Physics, A.U. College of Engineering, Andhra University,

Visakhapatnam-530003, India.

Abstract

Fine Nanoscale Particles of Mn(1-x)ZnxFe2O4 were prepared by chemical routeco-precipitation method. The structure of the samples are studied with X-raydiffraction (XRD) using Cu-K radiation and the Transmission ElectronMicroscopy (TEM).The XRD analysis confirms the formation of single phase

spinel structure. The morphology of the particles formed was examined bydirect observation by high resolution TEM. A narrow size distribution of theparticles was observed from this TEM micrograph. This suggests thatsynthesis method can provide well isolated homogenous size distribution ofparticles, will be useful for the Electrical and Magnetic study. The magneticproperties were studied using vibration sample magnetometer (VSM) andelectrical properties of the samples measured using standard two-probemethod.

Keywords: Co-Precipitation, Nano Particles, Hysteresis curves, soft ferrites.

IntroductionThere is an intense demand for high performance and miniaturization of manyelectronic devices, which exclusively needs soft magnetic materials with highpermeability. AB2O4 type of compounds with Spinel structure shows interestingstructural, electrical and magnetic properties, which vary with the nature of the ions,their charge and site distribution amongst tetrahedral and octahedral sites [1, 2].Various cations can be placed in A site and B site to tune its magnetic properties.Depending on A site and B site cations it can exhibit ferromagnetic,antiferromagnetic, spin (cluster) glass, and paramagnetic behaviour [3]. The generalcomposition of such ferrites is MFe

2O

4. Where M represents one or several of the


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52 D. Santhosh Kumar and K. Chandra Mouli

divalent metals. These types of ferrites have been extensively used in many electricaldevices because of its high permeability in the radio frequency region, high electricalresistivity, mechanical hardness, and chemical stability [4-6]. Among themManganese ferrite, Nickel ferrite, Zinc ferrite and Cupper ferrite are most popular andversatile which was investigated by many researchers. In this paper magnetic andelectrical properties of Mn1-xZnxFe2O4 are discussed thoroughly. The performance ofany ferrite is greatly influenced by its synthesizing technique [7-13]. The conventionalceramic method of preparation which involves solid stats reaction between oxides athigh temperatures is cumbersome, time consuming and does not always result in purereproducible product. Therefore, various non-conventional processing techniques[7-9], which are mainly solution techniques are reported. In the present work non-conventional preparation method, known as co-precipitation method, was used for

preparation of MnZn ferrite. Main advantages of this method is that it is inexpensive,time saving and results in superior properties of ferrites processed at much lowertemperature. The absence of ball milling in this method leads to stoichiometriccomposition as there is no possibility of loss or gain of material during milling, as incase of conventional ceramic method. In the present work magnetic and electricalproperties of Mn1-xZnxFe2O4 ferrite synthesized by co-precipitation method wereconsidered.

Manganese Zinc ferrites are widely used in electronic applications such astransforms choke coils and noise filters because of their higher permeabilities and lowmagnetic losses at high frequencies. Their properties largely depend on theirmicrostructure [14]. So the Nano-techniques were introduced to control their ultra

microstructure, instead of the traditional ceramic way. However, preparing a fine andagglomerate/aggregate-free powder is the first and perhaps the most important steptowards fabricating a ceramic material of desirable microstructure and their highsintered density, small grain size and narrow grain size distribution. FineNanoparticles of Mn1-xZnxFe2O4 with stoichiometric proportion (x) varying from 0.2to 0.8 were prepared by the chemical co-precipitation method. The samples werecharacterized utilizing x-ray diffraction (XRD), Transmission electron micrograph(TEM), vibrating sample magnetometer (VSM). The specific saturation magnetization(MS) of the particles was measured at room temperature. Electrical properties of thesamples measured using standard two-probe method.

ExperimentalMn- Zn ferrite of composition Mn1-xZnxFe2O4 Nano scale particles in the presentwork was prepared by co-precipitation method. The materials used were Manganesechloride ( 98.0% Merck, India), Zinc Chloride ( 99.1% Merck, India) Iron III chloride( 99 % Merck, India) and Sodium chloride ( 97 % Merck, India), were weighed out inthe required stoichiometric proportions and dissolved in distilled water, and NaOHsolution was added to this aqueous solution under continuous stirring with a constantspeed. The reaction temperature was maintained constant, with the dropping of themixed solution to the alkaline aqueous solution. The precipitation occurredimmediately and the color of suspension changed from the initially brown to dark


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Studies on Mn (1-x) ZnxFe2O4 Nanoparticles Synthesized 53

brown. It was kept stirred for 2h at constant temperature then it washed with distilledwater to remove sodium and chloride ions. The washed sample was dried in air. Driedsample was examined by X- Ray diffraction, Transmission Electron Microscope andVibration Sample Magnetometer. X-Ray powder diffraction using Cu-K source andestimation mean crystallite size. The estimation is made via Debye-Scherer formulausing the FWHM of the (311) peak of X- ray diffraction [14]. The morphologicalproperties of specimens are observed by TEM. The magnetization loop for the samplewas measured at room temperature using a vibrating sample magnetometer (VSM,JDM-13). Fine powders of Mn1-xZnxFe2O4 was mixed with 5% P.V.A binder andpressed into pellets of the size 10mm diameter and thickness range between 2 and 4mm under a pressure of 50 KN applied for 3 min. these pellets were sintered in air attemperatures 900, 1000, 1100, 1200, 1300OC respectively, for 2h, by setting heating

and cooling rate at 5

O

C per minute. The pellets were coated with silver paste on eitherside to establishing good ohmic contacts with the electrodes. Resistivity as a functionof temperature was measure by using standard two-probe method.

Results and DiscussionThe X-ray diffraction studies were carried out using Cu-K radiation with Philipspowder diffractometer and determined the crystallite size. We taken X-ray diffractionat room temperature, with a copper target, the wavelength is 1.5406 , shows that thesample have formed the single-phase spinal structure. Fig.1 shows the X-raydiffraction pattern of powder samples. The diffraction peaks corresponding to (220),

(311), (400), (422), (511), and (440) planes of polycrystalline MnZn phase areconfirmed. The crystallite size of Mn1-xZnxFe2O4 for the most intense peak (311)plane determines from the X-ray diffraction data using the Debye-Scherrer formula.

dRX = k/ cosWhere dRX is the crystallite size, k = 0.9 is a correction factor to account for

particle shapes, is the full width at half maximum of the most intense diffractionpeak (311) plane, is the wave length of Cu target = 1.5406 , and is the Braggangle. The average crystallite size of the prepared samples at preparation temperatureis 13-19nm. Lattice constant a for the samples was calculated from the observed dvalues and given in the Table 1. The shape, size and morphology of the particlesformed were examined by direct observation via high-resolution transmission electron

microscopy. The transmission electron micrographs of the prepared samples are givenin Fig. 2. Direct observations of the lattice image reveal that the particles areapproximately spherical in shape and agglomerated. Agglomeration of the preparedfine particles can be clearly noticed for the larger values of zinc concentration. Inother words, the decrease in particle size leads to greater agglomeration of magneticfine particles. Because of the smaller size, (single domain) particles experience apermanent magnetic moment proportional to their volume. Hence, each particle ispermanently magnetized and gets agglomerated.


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The densities of the sintered pellets were measured and kept in the Table.2. Thedensities of sintered Mn1-xZnxFe2O4 ferrite are found to be increased with the sinteringtemperature. The density may be attributed to the existence of phase transition whichoccurs during the crystal formation process while sintering. The investigation on finestructure of Mn1-xZnxFe2O4 ferrite clearly indicates the influence of sinteringconditions on the growth [15], density of the sample and crystalline phase of thesample [16]. The usual trend in the density values is also observed in the resistivitytrends of the samples. Fig.3 shows plots ofLog (ohmCm) V/s Temperature 1000/T(K) for Mn1-xZnxFe2O4 ferrite. A semiconductor like general behavior is seen for thesample as the samples undergo a second order ferrimagnetic to paramagnetic phasetransition.

Although the trends depend on the concentration of the Zn in the sample these are

more strongly dependent on the sintering temperature of the sample. Resistivityvalues at 300K are seen to vary between2.12 x106 ohm-cm and 1.898 x106 ohm-cmfor samples sintered at different temperatures the highest and the lowest beingobserved for 9000C and 13000C, respectively.

In ferrites electron conduction mechanisms have been studied by manyinvestigators and reviewed by Klinger et al. various models were proposed; however,the thermally activated hopping model is found to be more appropriate in explainingqualitatively the electrical behavior of MnZn ferrites. In the hopping process theadditional electron on a ferrous (Fe2+) ion requires little energy to move to an adjacent(Fe3+) on the equivalent lattice sites (B sites). In presence of the electric field, theseextra electrons hopping between iron ions give rise to the electrical conduction.

Therefore, any change in the (Fe2+

) ion content in the spinel ferrite lattice and/or thedistance between them is crucial to the intrinsic resistivity of MnZn ferrite grains,including the intrinsic grain boundaries. If the introduction of another cation into thelattice causes a change in the valency distribution on the B sites, then the number ofelectrons potentially available for transfer will be altered. On the other hand, theincorporation of foreign (addition of impurity) ions can change the distance betweenthe B lattice sites, which is crucial for the conduction mechanism. Thus, the formationof an intrinsic grain boundary in doped samples by the segregation of aliovalent ionsmust increase the resistivity. This gives rise to polycrystalline MnZn ferrite withnon-ferrimagnetic grain boundary, ferrimagnetic outer grain region and ferrimagneticconductive core. Thus the contribution to the bulk resistivity may be considered as

resistivity contribution coming from three different regions. To establish a relationbetween the Power loss due to eddy currents and the average grain diameter ahypothetical brick wall model is applied. As per the model each layer can berepresented by a resistancecapacitance (RC) lumped circuit of high Ohmic layers.When the resistivity of the bulk is much lower than the grain boundary layers, theequivalent circuit of the ferrite can be represented by a series of lumped RC circuitsof the grain boundary layers [17]. As the samples under investigation are sinteredfrom Nanoparticle MnZn ferrite in a reducing atmosphere with no additives there isno possibility of formation of high resistivity ferrimagnetic outer grain boundary.Thus the total contribution should come only from the non-ferrimagnetic grainboundaries and ferrimagnetic conductive core.


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In the cubic system of ferrimagnetic spinels, the magnetic order is mainly due to asuperexchange interaction mechanism occurring between the metal ions in the A andB sublattices. The substitution of non-magnetic ion such as Zn, which is having apreferential A site occupancy results in the reduction of the exchange interactionbetween A and B sites. Hence, by varying the degree of zinc substitution the magneticproperties of the fine particles can be varied. Fig.4 shows the room temperaturehysteresis loop of the prepared powder samples for various zinc substitution. Uponincreasing the partial substitution of zinc with manganese the specific magnetization(Ms), remanence (Mr), coercivity (Hc) and Curie temperature (Tc) decrease. Thevariation of coercivity and remanence with the increase in the zinc substitution areshown in Fig.5. The specific magnetization measured at 10 kOe was found to bemaximum (47 emu/g) for x = 0.4 and decreased on further increase in Zn

concentration (30 emu/g) for x = 0:8. The changes in the Saturation Magnetizationand Curie temperature with the degree of zinc substitution are given in Fig.6. Thechanges in magnetic properties such as Ms; Hc; Mr and Curie temperature Tc are dueto the influence of the cationic stoichiometry and their occupancy in the specific sites.In addition, formation of dead layer on the surface, existence of random canting ofparticle surface spins, non-saturation effects due to random distribution of particlesize, deviation from the normal cation distribution, presence of adsorbed water, etc.,were due to the reduction of magnetic properties of nanosized particles.

Table 1: Results obtained from the analysis of XRD.

Name of the Sample (hkl) d(Ao) DaveXRR ao

(a) Mn0.8Zn0.2Fe2O4 311 2.648 19 8.448(b) Mn0.6Zn0.4Fe2O4 311 2.643 17 8.440(c) Mn0.5Zn0.5Fe2O4 311 2.639 16 8.437(d) Mn0.4Zn0.6Fe2O4 311 2.635 14 8.426(e) Mn0.2Zn0.8Fe2O4 311 2.628 13 8.409

Table 2: Table showing density of Un-sintered samples and density of samplessintered at 900,1000,1100,1200, and 1300OC.

Zinc Count

(x)

Un

Sintered

900 C

density

(g/cc)

1000 C

density

(g/cc)

1100 C

density

(g/cc)

1200 C

density

(g/cc)

1300 C

density

(g/cc)

0.2 2.7512 3.982 4.1854 4.3020 4.3893 4.45620.4 2.696 3.7536 4.1127 4.2953 4.3512 4.36230.5 2.396 3.6226 4.0987 4.1287 4.2163 4.24010.6 2.3941 3.5169 3.9833 3.9909 4.1214 3.92510.8 2.3273 3.1825 3.8471 3.8674 4.1037 3.9222


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Figure 1: Indexed XRD pattern for Mn (1-x) ZnxFe2O4 with x varying from 0.2 to 0.8.,(a) Mn0.8Zn0.2Fe2O4, (b) Mn0.6Zn0.4Fe2O4, (c) Mn0.5Zn0.5Fe2O4, (d) Mn0.4Zn0.6Fe2O4and (e) Mn0.2Zn0.8Fe2O4.

Figure 2: Transmission electron micrograph of the prepared samples (a)Mn0.8Zn0.2Fe2O4, (b) Mn0.6Zn0.4Fe2O4, (c) Mn0.5Zn0.5Fe2O4, (d) Mn0.4Zn0.6Fe2O4 and(e) Mn0.2Zn0.8Fe2O4.


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1.0 1.5 2.0 2.5 3.0 3.5

1

2

3

4

5

6

7

8

Log(ohm-Cm)

Temperature 1000/T(K)

0.2 Zn

0.4 Zn

0.5 Zn

0.6 Zn

0.8 Zn

1.0 1.5 2.0 2.5 3.0 3.5

1

2

3

4

5

6

7

8

9

0.2 Zn

0.4 Zn

0.5 Zn

0.6 Zn

0.8 Zn

Log(ohm-Cm)

Temperature 1000/T(K) Figure 3a: Plots ofLog V/s 1000/T forMn1-xZnxFe2O4 ferrites sintered at 900OC.

Figure 3b: Plots ofLog V/s 1000/T forMn1-xZnxFe2O4 ferrites sintered at 1000OC.

1.0 1.5 2.0 2.5 3.0 3.5

1

2

3

4

5

6

7

0.2 Zn

0.4 Zn

0.5 Zn

0.6 Zn

0.8 Zn

Log(ohm-Cm)


1.0 1.5 2.0 2.5 3.0 3.5

1

2

3

4

5

6

7

0.2 Zn0.4 Zn0.5 Zn

0.6 Zn0.8 Zn

Log(ohm-Cm)


Figure 3c: Plots ofLog V/s 1000/T forMn1-xZnxFe2O4 ferrites sintered at 1100

OC.Figure 3:d: Plots ofLog V/s 1000/Tfor Mn1-xZnxFe2O4 ferrites sintered at

1200 OC.

1.0 1.5 2.0 2.5 3.0 3.5

1

2

3

4

5

6

7

8

9

0.2 Zn

0.4 Zn

0.5 Zn

0.6 Zn

0.8 Zn

Log(oh

m-Cm)


Figure 3e: Plots ofLog V/s 1000/T for

Mn1-xZnxFe2O4 ferrites sintered at 1300OC.

Figure 4: Hysteresis curve of theprepared samples Mn(1_x)ZnxFe2O4 (x =0:2-0:8) measured at room temperature.


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0.2 0.3 0.4 0.5 0.6 0.7 0.8

0

2

Mr

Hc

Zinc ConcentrationRemanencemagnetization(Mr)

(emu/g)

8

10

12

14

Coercivity-Hc(Oe)

0.2 0.3 0.4 0.5 0.6 0.7 0.8

28

30

32

34

36

38

40

42

44

46

48

Ms

Tc

Zninc Concentration

SaturationMagnetization(Ms)(

emu/g)

150

200

250

300

350

400

CurieTemperature(Tc)(oC

)

Figure 5: Variation of coercivity andremanence with the increase in the zinc

substitution.

Figure 6: Changes in the SaturationMagnetization and Curie temperature

with the increase in the zinc substitution.

ConclusionIn the present work Mn1-xZnxFe2O4 ferrite Nanoparticles are prepared using co precipitation method. The average crystallite size of the sample is 13-19 nm. Andthese values are having excellent agreement with TEM image. The saturationmagnetization (Ms), remenant magnetization (Mr), and coercive force (Hc) areobserved. And the investigations on the resistivity of the Mn1-xZnxFe2O4 ferritedeveloped by sintering Nanoparticle Mn1-xZnxFe2O4 ferrite, prepared by co precipitation method, show existence of phase transitions thus contributing to

amazingly high electrical resistivity in comparison to the reported values. This is avery important parameter in minimizing the eddy current losses in power applications.It is evident that the material prepared by sintering nanomaterial MnZn ferrite notonly gives low loss material but also produces material with small grain size withlarge surface area as the grain growth is suppressed due to phase transitions. Thisfeature can have remarkable effect on the other properties of the material. Thesemiconductor like behavior of the esistivity shown by this material makes it afavorable material for sensor applications.

Acknowledgementone of the authors D. Santhosh Kumar gratefully acknowledges UGC-SAP (INDIA),for the financial assistance received through SAP Sponsored Research Fellowship inScience for Meritorious Student. And also thank full to Dr. M. R. Panigrahi, FormerCS I R Scientist, Who given continues support in doing my Research work.

References

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[2] J.B. Goodenough, Mag. Chem. Bond, John Wiley, New York, London, 1963,p. 120.

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(2004)1273.[5] A. Goldman, Handbook of Modern Ferromagnetic Materials, Kulwer

Academic Publishers, Boston, USA, 1999.[6] R. Valenzuela, Magnetic Ceramics, Cambridge University Press, Cambridge,

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and Product Technology, 1994, 9(4 - 6): 265 ~ 280[15] Makovec D, Drofenik M, Znidarsic A (2000) Aa I-8 Digest of 8th Int. Conf.

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Studies on Mn(1-x)ZnxFe2O4 Nanoparticles Synthesized by Co-Precipitation Method