I .1-1

Proceedings

of the OAE Solid State Physics

Symposium

(2005)

Structural and Magnetic Properties of Cu-Zn Fcrritcs M.Sultan and R.Singh School of Physics, University ofHyderabad,

Central University P.O., Hyderabad 500 046, India Abstract

Single phase spinel copper-zinc fe/rites system CII/.X'Lnx Fe]O. f.¥= V.V - I.V in slep ofV.I) were prepared IIsing the conventional double sinlering ceramic technique with final silllering tempera11l/'e of / {){){)°C.Sll1lctlira/prope/'ries sllch as lallice parameters and X-ray del/siry hal'e heen estimated. The lallice parameter increases wilh increasing 7.inc content. The morp/IOI0K!' (if the samples investigated hy SElv! shows the al'erage grain sizes beeween I- 5J1t11.The EDAX re51dts show good homogeneity o/the samples. Tile magnetic parameters like saturation maguetization and coercipe force were measured for all composiriolls at room temperature. The magnetic moment increases ulitli IJlcreasing x according 10 collinear ;Veel theory ojjerrimagnetism lip to x = 0.4. For x >0.4 it decreases in accordance with YajetKittel model. INTRODUCTION

small quantity of polyvinyl alcohol PVA was added as a binder agent. The granulated powders pressed into pellets (1.3cm diameter and -D.3cm thickness) followed by the final silllcring at 1000°C for 12h. 111Csamples were then slowly cooled to room temperature. All samples sinkred at 900 'C were investigated by X-ray dilTraction using Co Ka radiation (I- = 1.7R97A) Jncl XRG 3000 to cvidcncc thc singlc-phasc stmctmc. 111e values of X-ray density dx of dilTer.:nt compoSItions calculated from the relation dx=RMINa3 where M is the molecular \veight, N is Avogadro's number and a is lattice parameter. 111e microstructure of tile sllltered muterials wus examined by scunning .:Iectron microscopy SEM. The characterization of the samples was completed by the EDAX analysis that conlinned the different concentration of Cu, 7,n, Fe and 0 1Il all the samples. The magneti7.ation measurement, of all samples were carned out at room temperanue usmg vibratlllg samplc magnctometer (VSM).

Ferriks are the mixed mdal oxides containing iron oxide as their main component. The practical ferrites are always obtaincd by propcr mixing ofthc fcrritcs [I]. 111C magnetic propcrtics of fcrritcs arc highly scnsitivc to thc teclmology parameters, especially to the sintering conditions and the amOWll of constiment metal oxides. 111e nonmagnetic 7,inc substitution in M-fenites (M= Mn, Ni, Cu ... ctc) has intcrcsting effcct on thcir propcrtics likc magnctic ordcring, pCl1ncability, cocrcivity, porosity and controllcd microstmcturc giving them preferred wide use for many years as high frcqucncy dcvices such as radio frequcncy coils, transformer corcs, antcnna rods ctc [2,31. 111e spinel stnlcture can be considered as two magnetic sublattices: an A- or tetrahedral site surrounded by lour oxyg.:n ions and B- or octahedral site which is sun'olmdcd by six oxygen ions. 'l11Ccation disl1ibution among II and B sitcs dctcl1n inc thc magnetic propcrtics of spinel ferrites [/1]. The magnetic properties described by thc hystcrsis loop arc highly dcpcndcnt on both thc llll1insic properties of the materials (crystal stl1lc111reand composition) and on such extrinsic properties as grain size and d.:nsity [5J. Th.: alln OfUlis pap.:r is to study the crystal structurc, dcnsity and microstmctmc with .Ithc ~---hyst.:rsis parameters of all compositions of tile system CUI.xZnx Fc20.! at room tcmperaturc.

__~_I

I

AND DISCUSSION

The XRD paltems oj' tirree compositions ar.: ShO\\11 in Fig 1.

-.--

0-

I"

J:

-.r

other

~Z)

I ••••••••f-

"1

:1· 00

2i):C

obtained at room

~lro

x

~l " :1 (~

C

'i

too,

3

clarity the in frg.3.

.20O.4 can be explained

in

terms of spin struehlre changes from t\vo sllblattices Ned .(,,;ol1int:ar structure to three sublattJces with triangular arrungcment having 1l01l collinear Yard - Kittel canted spin struehlre on B-sublattice [2,6,7]. for the samples with x ::.0.7 the magnetization increases with the applied magnetic lield so that the sanlration magnetization could not be reached in the applied field up to 5kOe. CONCLUSIONS The whole runge compositions or CUI.X lnx Fe,O, ferrite ~amples prepared by slandanJ ceramic method shuw ~illglephasc spinel structure. The lattice parameter increases linearly \-vith increasing X valve oht:ying Vigard's law. Saturation magnetization reaches maximum at X .= OA which may be attributed to Iransition from collinear to non· collinear spin stnlcUlre arrangement. Coerci\'ity is small und ils del;reasing trend wilh increasing X may he due to the decrease of the magnetic anisotropy as a result of increasing zinc content.

REFERENCES I.

.J.Smit, Magnefic Properties oj Materials, }v1cGraw llill New York. 1971

2.

M.ll.Rana.

--r-'.)r. ~:X(l

Fi/lla (OcfiOlil;:li

·~"'07. -.6.···)",,04

to the

Zn /~Fe

attributed to the larger ionic size of In'+ (0.82A) than that ofCu'+ (0.70A). Fig 3 shows the M-H loops for six samples

for sake of are not included

attributed

la

The rednction Fig. 2. Variation of lattice parameter Cu7.n ferrite system

are

1Il an increase in magnctic momcnt on B· and increase in the net saturation Inngnetizntion

Zmc Content X

".

-----

moment IlB magnetic

'J."'~" ~l"c.

".

'i'

c o

of Cu, ..

'"

'" 1

" .."

40.169 60.9182.61 62.1662.67 55.8382.4 0.714 0.575 1.8402 0.837 1.007 58.481 2.51 1.7604 38.2931.64 51.3842.2 «k) I I27472 H, Saturation I Cot:n.:ivit)

T

and Coereivity

is almost

~~~ ~

Magnetization

·~;;:06 ,~·"'-~~O.2

In ferrites at R.T

It is dear Lhat each loop shows low coerci viI)' He and remanence indicating that all the samples belong to family at soft territes. The variation of eoercivl!)' He l1R \vas obtained from saturation magnetic moment

M. Islam, 1. Ahmed.

Magn. Mater.

low the and the

hystersis loops as a tlmetion of ln content and listed in tablel. It is observed that lIe decreases with increasing In content. This may be attributed to the decreasing of the magnetic anisotropy due to increasing grain size with increasing Zn content. Ms and nB increase \vith increase in In content np to 40%. For higher ln content these parameters show decreasing trend.

and T.Abbas,

.J.

J Alloys

Camp. 291 (1999)208

3.

D.Ravinder,

,1.

Wijn, Ferrites, Philips' Libra!)' ./:.·indliol'en(Holland). 1959 1. Smit

and

H.P.T.

5.

L.W. Gorter, Philips.

6.

N.S. Satya MUlthy et aI., Phys. Re\'. 181 (1969)

7.

Y. Yalet and C. KitteL Phys. Re\'. 87(1952)

692

Magn.

187( 1998) 242

Res. Rep. 9(1954)

tech.

295

29

969

Proceedings of DAE Solid State Symposium (2006)

Dielectric Behaviour in Cu-Zn Ferrites M.Sultan and R.Singh School of Physics, University of Hyderabad, Central University P.o., Hyderabad 500046, India. Email: [email protected] Abstract Room temperature dielectric constant £' and loss tangent tanD of the spinel copper-:::incferrite system have been studied as a jill1ction of composition in the frequency range 60H:::to 10MH:::.High values of the order of Irl - 10./ of £' and its high frequency dispersion in the low frequency range is eJ.plained in terms of Koops theOlY. All samples exhibit normal behaviour of £' and tanD with frequency. Their values decrease with increase in :::inccontent up to x = 0.6followed by an increase with further increase in x value. This could be attributed to the existence of two types of charge carriers created during the sintering process. TRaDUCTION

data using the relation E' = Cp t IEoA where Eo is the permittivity of the free space, t is the thickness of the sample and A is the surface area of the sample. The drive voltage of the LCR meter used was 0.5 volt.

• containing ferrites are widely used in high ,uency and electronic devices because it combines electrical resistivity with useful magnetic and ~ctric properties that depend on several factors as sintering process and chemical composition The study of the frequency variation of dielectric rties of territes, such as dielectric constant and - tangent is significant from the fundamental and ical point of view. Fundamentally, it provides Ie information on the behaviour of localized

RESULTS Figure

I shows the variation

of the dielectric

constant

E' of

this system as a function of frequency. It is observed that the dispersion behaviour exhibited by these samples is normal i.e. the values of E' decreases with increasing frequency, and shows ;,imilar behaviour for all compositions in the whole frequency range. The decrease in the values of E' is rapid in the lower frequency range then becomes slow at higher frequency to reach a fairly constant value in the MHz frequency range.

ge carriers, leading to a good understanding of the .hanism of the dielectric behaviour in this kind of ~rials [2]. Technically, it reveals wealth :mation for the usefulness of these materials

AND DISCUSSION

of for

us applications especially at higher frequency the effect of the frequency on the resistivity can ":lther large .The aim of this work is to study rnatically the room temperature dielectric crties of Cu-Zn ferrites as a nmction of frequency

.-;e

0C() 10' U Q) is U u; 102 Q)

10'

-u-IOMHz) .

~

103

ERIMENTAL polycrystalline compounds CUI_XZnx Fe204 (X= 3,0.4,0.5, 0.6, 0.7, 1.0) were prepared using the entional double sintering ceramic technique for . oxides in air with the final sintering at 1000°c for urs. All samples were investigated by X-ray _~tion using Co K. radiation (A = 1.7897 A) INEL ~ 3000 to evidence the single-phase structure. surfaces of pellets of· -1.2cmdiameter were ed up to thickness of - 0.1 cm and coated with paste to ensure good electrical contacts for ing the dielectric properties. The room rature dielectric properties were carried out by ~ing the parallel capacitance Cp and loss tangent of the samples in the frequency range 60Hz ::'-Iz using a FLUKE (PM6304) LCR meter. The crric constant E' was calculated from Cp and tano

10'

10'

10'

10'

10'

107

Frequency (Hz) Fig.1. Frequency dependence of dielectric constant of CU,.,Zn, Fe20. The observed

high values

of the order of 102 - 104 of

the E' as well as the dispersion in low frequency range can be explained in terms of Koops theory, which is based on the Maxwell-Wagner type interfacial space charge polarization for inhomogeneous nature multi-

675

layer dielectric structure [3]. Accordulg to this model, it is assumed that the dielectric structure is composed of well conductulg ferrite grauls, which are separated by poorly conducting thin layer graul boundaries, such as an equivalent of a resistor and a capacitor.

increasing frequency. 'nle same behaviour with lugh values of tano for some compositions of this system has been reported eaTlier [6, 9].The high values of lanD maybe due to the higher concentration of charge carriers that are fonned durulg sinlering in the present samples. 10;,

Both the dielectric constant and electrical conductivity are basically electrical properties and it has been recognized that the same mechanism viz. exchange of charge carriers between ions, is responsible for both the phenomena. A strong correlation between conduction mechanism and the dielectJic behaviour of ferTites has been established by Iwauchi [4} and Rezlescu and Rezlescu r5]. When an electric field is applied, it could ulduce a local displacement of charge carriers ill the same direction or in the opposite direction of the applied field, dependulg on the type of charge carrier. The two types of charge carrier exchange III tlus system arc Fe2- "" Fe3T and These local displacements cause the polarization Ul ferrites. Under the applied field, the diITerent conductivity regions will affect the charge carTiersthrough hoppurg to reach and accumulate at the separatillg bOlmdaries.The build up of charge carriers at the interfaces corresponds to a charge polarization and dielectric constant. The grain bOUlldaries of lower conductivity were found to be eITeetive at lower frequencies, with the high values of dielectric constant, while ferrite grains of highly conducting nature are effective at lugher frequencies [6]. Cul+""

, ~

10'

"-

~

'''-,:""

-~ ~ ''''''. ~.•..

---

""'~,

-~

"~~~

.~~~, 10'i _ •.~~. 210,

~

~X=0.5

10-'

~'~".~

"'''~

--....

"",.~ '-""''''',,-''0 ~ ~

""'''-~''-, "', u...;;"",,::-....

X=0.7

~-O

'-

'" -"~~'~'~-"e~~~o_ ~ "'-,

~

'"

X=O.4 x ~X=1. = 0.6

.••. ~~~.

.•....•

....¢•• 'o~

'~~~,,\ •.•... "'~

Cu2·.

The lower values of dielectric constant at high frequencies could be attributed to that when the jumping frequency of electric charge carriers CaIUlOtfollow the alteration of applied AC electric field beyond a critical frequency and the probability of charge carriers reachillg the grain boundaries decreases resulting Uldecreasing the polarization and dielectric constant. DIe results obtained Ulthe present work and the explanations given above are ul good agreement \\ith those reported earlier bv Koops and others [3,7]. "DIe n0TI1131dielectric behaviour in ferrites is clearly ShO\\11 ill figure 1 where no relaxation peaks are observed. This maybe due to the lower sinterlllg temperature (1000°C) for these materials compared to that obtailled earlier [5] for the SaIne compositions of the system. The lower surtering temperature means rew Fe2' ions that can be fonned. From the present data it can be conclnded that at low substitution of Zn2+ i.e. up to x = 0.6 only p-type of charge carrier would be domulant. For lugher Zn content leading to illcrease Ul g' value is due to dominant n - type carriers. The values of f.' in the n-type side are not as lligh as reported for other Zn ferrites [6, 7] which were sintered at high temperature (~ 12()()°C). The dielectric loss arises due to lag of the polarization behuld the applied altematillg electric field and is caused by the illlpurities and unperfections UIthe crystal lattice [8]. The variation of loss angle tanb \\ith freqnency is sho\\TIill figure 2. It can be seen that none of the sanlples show relaxation peak behaviour and tanb decreases with

10"

10'

10'

10'

X=0.3

10'

Frequency (Hz) Fig.2.Frequeney dependence

10'

~,~ 0

"", 10

of dielectric loss

tangent of CU",Zn, Fe,O.

The dielectric loss Ul fen'ites is generally reflected Ulthe resistivity measurement, whcre the materials with lower resistivities exhibit higher dielectric loss. The resistivity measurements are in progress to understand the dielectric loss mechanisms ill the present system. CONCLUSIONS

Room temperature dielectric constant c' and loss tangent tanD of the spinel copper-zulc ferrite system have been studied as a function of composition in the frequency range 60Hz to 10MHz. High values of the order of 102 104 of g' and its lugh frequency dispersion ill the low frequency range is explained in tenns of Koops theory All samples exlubit nonllal behaviour of g' and tanDwith ti·equency. Their values decrease with increase in zinc content up to x = 0.6 followed by an illcrease 'Withfurther increase in x value. This could be attributed to the existence of two types of charge carriers created during the silltering process. REFERENCES

1.L.G. Van Uitert Proc. IRE 44 (1956) 1294 2. A Y. Lipare, P.N. Vasambekar, and A.S. Vaingankar 1. Magn. Magn. Mater. 279 (2004) 160. 3 e.G. Koops Phys Rev. 83 (1951) 121. 4. K. lwaucJu , Japn. 1. Appl. Phys. 10 (1971) 1520. 5. N. Rezlescu and E. Rezlescu Phys. Stat. Sol. (a) 23 (1974) 575. 6. AM. Abdeen 1.Magn. Magn. Mater. 192 (1999)121. 7. MA EI Hiti 1. Magn. Magn. Mater. 192 (1999) 305.. 8. A. Venna, T.C. Goel, RG. Mendiratta and M.I.Alam Malter. Sci. Eng. B 60(1999) 156. 9. HM. Zaki Physica B 363 (2005) 232.

676

Proceedings

of the DAE Solid Slate Physics Symposium

(2007)

Synthesis and EPR Studies of Zinc Ferrite N anoparticles M. Sultan and R. Singh School of Physics,

University

of Hyderabad,

Central University

P.O., Hyderabad

500 046, India

Email: [email protected] Abstract The single-phase ZnFel0, nanoparticles have been 5)1nthesized using co-precipitation process at RT The coprecipitated mean particle size calculated fi'mn X-ray diffraction is found to be around 5 nm. The particle sizes could be controlled in the range of 5-30 nm by a suitable heat treatment at temperature rangingfi'om RT to J 200 K. The temperature dependent EPR studies were carried on ZnFe204 samples as a function of particle size in the temperature range J 20-500 K. The EPR linewidth increases with increase in particle size. The resonance field shifts towards the lower value with decrease in temperature. The line broadening and shift to lower magnetic fields with decreasing temperature observed for all the particle sizes is ascribed to superparamagnetic behavior of nanoparticles.

RESULTS

INTRODUCTION .. ano-size zinc ferrite ZnFe204 has been a particular subject of study by numerous researchers because of its unusual structural and magnetic properties as compared to that of bulk material [I). The magnetic properties of ultra fine particles are strongly influenced by finite size effects where It exhibits unique phenomena like superparamagnetism [2]. ~1agnetic resonance is a powerful technique to study the magnetic compounds including their magnetic ordering :ransitions [3). In this paper, we present the temperature .:!ependent EPR studies of as co-precipitated zinc ferrite noparticles.

,~COprecil"itnted

~ ~

Calcined

at 500QC

Calcined

at 700°C

Calcined

at 900"'C

Ceromic

Standard

"'-

j

EXPERIMENTAL -;ne zinc ferrite nanoparticles were prepared by :oprecipitation of an aqueous mixture of metallic salts (zinc :rates Zn(N03h.6H20 and ferric nitrates Fe(N03h·9H20 Zn:Fe = I :2)) in an alkaline medium (NaOH). The -'urion of metallic salts was poured quickly into the ing alkaline solution under vigorous stirring. The ing temperature was maintained at 85C for 6h. The pH e of the solution was adj usted to be more than I O. The :-xipitate was then filtered and washed several times with ~Ied water until the pH value become 7. A precipitate -~ined from the co-precipitation technique was dried in

2,;

Fig. 1: XRD patterns of zinc ferrite nanoparticles

80C il'l an electrically heated oven for 18h. X-ray er diffraction patterns were recorded using Co Ka ion source (A = 1.7897A) Inel XRG3000 -~ctometer. Electron Paramagnetic Resonance (EPR) ~ements were performed at room temperature as well the temperature range (120 -500K) on a JEOL,jpS ESR spectrometer with a resonance cavity of -GHz. :!'r

AND DISCUSSION

Figure 1 shows the XRD patterns of co-precipitated zinc ferrite nanoparticle. A broad single-phase .XRD peak corresponding to the spinel zinc ferrite was observed. This broadening decreases as heat treatment temperature IIlcreases.

This indicates the growth of crystallinity in the powders as well as the particle size with increase in heat treatment temperature. The broadening in XRD peaks may come from different sources namely; the main contributors are the reduced particle size and strain in the crystal. The mean particle size of the samples was estimated from the full width at half maximum of the most intense reflection peak using Scherrer's formula D = 0.9 AJ~ cose where D (nm) is the apparent particle size, A is the wavelength, ~ is the full width at half maximum in radian, and e is the diffraction angle of the most intense peak (311). These studies reveal that with the increase in the calcination temperature the crystallite size gradually increases for all the powders.

257

The average particle size of the powders prepared at different temperature with varying calcination temperature as estimated from X-ray spectra are shown in table! Tablel:

Structural and ESR parameters of coprecipitated zinc fenite nanoparticles

Heat 8.471 size value 32730 2.01 510(A) 8.447 143.6 Ho 325 321 2.04 J.OI 51.9 Lattice 8.461 32520 8.455 99.6 52.4 327 2.00 41.3 (mT) (mT) paramet ger I1Hpp oPalticle (nm) 500

8.440

this temperature (figure 4). The non-Ii near temperature dependency of HR in nanometer size ZnFe204 suggests that the surface anisotropy becomes dominating on the magneto-dynamics of nanoparticles when the diameter of the nanoparticle is smaller than the critical size (The effect of large surface area to volume ratio) [5]. The detailed analysis of the data is in progress. A~

~~ >="

,

.s :a

~~ ~

50

~

A "'4

AA A .:0",-

4A .1:1."'..::.."",,"..:1.

20

I

,

I

r

250

Figure 2 shows the EPR spectra of zinc ferrite nanoparticles as a function of particle size. All the spectra show a single broad signal indicating the complete formation of the compound and absence of isolated Fe3+ ions. The resonance linewidth I1Hpp increases with increase in particle size. There is no significant change in g - value as a function of particle size (table I). A good correlation can be noticed between resonance linewidth and particle size in this

300

Temperalure

Fig 3: Temperature

dependence zinc ferrite nanoparticles

[

350 (OK)

of resonance

linewidth

of

'"

~~~~~~~~~~~~~~~~~~~~~

3" A""a'"

>="

.§..

324

Q)

322

"

x·

compound.

Ii:

~~

B ffi

~

~~

320

~

a:

31.

"

100

~~

150

Calcined at soo"c

.~ ];;

200

250 Temperature

Fig. 4: Temperature ferrite nanoparticles

As cQprecipitated

dependence

350

400

450

500

(OK)

of resonance

field of zinc

CONCLUSION ~e,"m;csamPle 600

200

800

Field intensity (mT)

Fig. 2: ESR spectra of zinc function of heat treatments

ferrite

nanoparticles

as a

The temperature dependence of I1Hpp and resonance field for sample with 5 nm palticle size is shown in Figure3 and 4. The I1Hpp decreases with increasing temperature up to 250K then start increasing. The reduction of I1Hpp with decreasing temperature is due to the variation of both the magnetization and anisotropy [4]. The large values of L',Hpp and g-factor at low temperature are attributed to stronger dipole-dipole interactions. With increasing temperature, this interaction decreases resulting in decreasing of L',Hpp and gfactor. The increase of L',Hpp with temperature above room temperature could be due to thermal broadening. The slightly with decreasing resonance field HR decreases temperature down to 230K followed by a decrease below

The single-phase ZnFe204 nanoparticles have been synthesized using co-precipitation process at RT. The coprecipitated mean particle size calculated from X-ray diffraction is found to be around 5 nm for the as prepared sample and it increases with heat treatment. The EPR linewidth increases with increase in particle size .The line broadening and shift to lower magnetic fields with decreasing temperature could be attributed to superparamaglletic behavior of nanoparticles. REFERENCES 1. 2. 3. 4. 5. 6.

258

Oliver et aI, App. Phys.Lett. 76 (2000) 2761 V. K. Sharma and F. Waldner, J. App1. Phys. 48 (1977) 4298 K. H. Wu et, App1. Surface Sci 228 (2004) 285 P. Kirrani et a1. J. Magn Magn mater 252 (2002)35 R.Berger et al J. Magn. Magn. Mater 234 (2001)