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Materials Chemistry and Physics 131 (2011) 413–419

Contents lists available at SciVerse ScienceDirect

Materials Chemistry and Physics

journa l homepage: www.e lsev ier .com/ locate /matchemphys

tructural and vibrational properties of ZnxMn1 − xFe2O4

x = 0.0, 0.25, 0.50, 0.75, 1.0) mixed ferrites

inesh Varshney ∗, Kavita Verma, Ashwini Kumarchool of Physics, Vigyan Bhawan, Devi Ahilya University, Khandwa Road Campus, Indore 452001, India

r t i c l e i n f o

rticle history:eceived 3 May 2011eceived in revised form 16 August 2011ccepted 27 September 2011

eywords:hemical synthesisowder diffraction

a b s t r a c t

In this paper, we report the variations in the crystal structure, average crystallite size, Raman spectra andmagnetic properties of ZnxMn1 − xFe2O4 (x = 0.0, 0.25, 0.5, 0.75, 1.0) mixed ferrite samples synthesizedby chemical co-precipitation method. The X-ray diffraction pattern confirms that the mixed ferrite sam-ples are in cubic inverse spinel structure, which is further validated by Rietveld refinement. The oxygenposition, the lattice parameter, and the cation distribution have been determined by means of Rietveldanalysis, indicating the existence of mixed ferrites in all samples. The final structure was refined in spacegroup Fd3m. The structural studies identify the decrease of lattice parameter, whereas the crystallite

aman spectroscopy and scatteringössbauer spectroscopy

size increases and porosity decreases on increasing the Zn concentration. IR spectra confirm vibration ofFe2+–O2− bond at tetrahedral (A) site. The Raman spectrum reveals active phonon modes at room temper-ature and shifting of modes toward the higher frequency side on moving from MnFe2O4 to ZnFe2O4. Thetransmission Mössbauer spectroscopy determines the site preference of the substituted ions and theireffect on the hyperfine magnetic fields. The results showed that all the samples are superparamagnetic

in nature.

. Introduction

Ferrites are common magnetic iron oxide possessing a cubicpinel structure with a generalized formula AB2O4 as spinel ferrite.he structure of ferrites is almost perfect interstice cubic closed-acked oxygen arrangement, in which 8 tetrahedral sites (A –ite) are occupied by Fe2+ ions and 16 octahedral sites (B – site)re equally occupied by Fe2+ and Fe3+ ions [1]. The uniqueness ofagnetites is a normal spinel structure when doped with a diva-

ent transition metal occupying the tetrahedral site, while to thatnverse spinel structure results with an occupation of divalent tran-ition metal at the octahedral site. The situation becomes complex,s divalent transition metal ions enters on both A and B sublattices,eading to a mixed or disordered structure and is being focusedn the recent past not only on the bulk samples but also on theanosized crystals [2].

The substitution at Fe site causes the cation distributionetween tetrahedral (A) and octahedral (B) sites, which is effective

n revealing the structural and magnetic properties. Zinc-doped fer-ite (ZnFe2O4) is a normal spinel structure, where Zn2+ preferably

ccupy the tetrahedral sites due to their affinity for sp3 bondingith oxygen anions leaving all the ferric ions on the octahedral

ites. The normal spinel structured ZnFe2O4 is antiferromagnetic in

∗ Corresponding author. Tel.: +91 731 2467028; fax: +91 731 2465689.E-mail address: vdinesh33@rediffmail.com (D. Varshney).

254-0584/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.matchemphys.2011.09.066

© 2011 Elsevier B.V. All rights reserved.

nature due to low Neel temperature and is paramagnetic at roomtemperature due to weak superexchange interaction attributed to90◦ angle in Fe3+–O–Fe3+ [3]. Furthermore, for Mn doped MnFe2O4,it is argued that the cation distribution is random either at tetrahe-dral (A) or at octahedral (B) sites [4].

Zinc doped manganese ferrites with spinel structure are tech-nological important due to its applications in information storage,electronic devices, magnetic resonance imaging (MRI) contrastagent, medical diagnostics, drug delivery and others. It is relevant tosynthesize particles with narrow size distribution to meet the tech-nological challenge. Furthermore, the doped ferrites are well suitedfor cores in inductive components at high frequencies because theelectrons are scattered at the grain boundaries of nanostructurematerials, which reduces eddy current losses in electrical applica-tions. The nanosized and single domain nature of ZnxMn1 − xFe2O4ferrites result in the unique superparamagnetic properties [5].

In the recent past, the literature witnesses several tech-niques for synthesizing magnetic nano particles as spray pyrolysis,microwave irradiation of ferrous hydroxide, micro emulsion tech-nique and hydrothermal preparation technique [6–9]. However,co-precipitation method has advantages of being relatively simplertechnique and effective control over particles properties. Raman isthe powerful probe to reveal the vibrational and structural prop-

erties. At room temperature five Raman active modes of Fe3O4 at670 cm−1 (A1g), 410 cm−1 (Eg), 193 cm−1 (T2g(1)), 540 cm−1 (T2g(2)),and 300 cm−1 (T2g(3)) are predicted according to group theory[10]. Mössbauer spectroscopy is useful to investigate the magnetic

4 istry and Physics 131 (2011) 413–419

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14 D. Varshney et al. / Materials Chem

hases and to identify the Fe distribution at tetrahedral (A) andctahedral (B) sites [11]. The Mössbauer spectrum for other substi-uted cation such as (Co, Ni, Zn, etc.) infers that they were uniformlyistributed over the system while cations such as (Mn, Cd, Cu, etc.)ave the tendency to accumulate on the particles surface [12].

In view of the fact that there is diverse research related tohe structural parameters of ZnxMn1 − xFe2O4 ferrite, but litera-ure related to synthesis temperature, site occupancy and cationrdering is rather scarce. In order to explore variation of structural,ibrational and magnetic properties of ZnxMn1 − xFe2O4 ferrites, aeries of ZnxMn1 − xFe2O4 (x = 0.0, 0.25, 0.5, 0.75, 1.0) ferrite haseen prepared by chemical co-precipitation method and were fur-her characterized by various techniques such as X-ray diffractionXRD), Raman spectroscopy, FT-IR and Mössbauer spectroscopy.

. Experiment

.1. Chemicals

For the synthesis of manganese ferrite, zinc doped manganeseerrite and zinc ferrite nanoparticles Mn(NO3)2, Zn(NO3)2·6H2O,e(NO3)3·9H2O, sodium hydroxide, and acetone were used, whichere procured from e-Merck. All the chemicals were GR grade andsed without any further purification. The water used in all thexperiments was distilled with lower conductivity.

.2. ZnxMn1 − xFe2O4 preparation

ZnxMn1 − xFe2O4 fine particles were synthesized by chemi-al co-precipitation technique [13,14]. The aqueous solution ofinc, iron and manganese salts were freshly prepared by tak-ng Zn(NO3)2·6H2O, Fe(NO3)3·9H2O and Mn(NO3)2 in appropriate

olar ratio. This mixture was heated until the temperature reached0 ◦C [15]. While stirring, the pH of the above solution was raised to2 rapidly, by the addition of 6 M NaOH. The particles settled at theottom were collected and the top water layer with excess saltsas discarded. The particles have been washed repeatedly withistilled water to remove salt impurities. Later, the water washedarticles were treated with acetone dried at 300 K and calcined at00 ◦C for 5 h.

.3. Characterization

.3.1. X-ray diffraction (XRD)The XRD measurements were carried out with Cu K� (1.5406 A)

adiation using a Rigaku powder diffractometer equipped with aotating anode scanning (0.01 step in 2�) over the angular range0–80◦ at room temperature to identify the phases present. Therystal structure, lattice parameter, average crystallite size andorosity of ZnxMn1 − xFe2O4 ferrite series have been determinedt room temperature. Later on, the Rietveld refinements have beenerformed using Fullprof suite program in order to determine theiffraction parameters.

.3.2. Fourier transform infrared spectroscopyRoom temperature Fourier transform infrared (FTIR) spectra of

he ZnxMn1 − xFe2O4 ferrites were recorded in the frequency rangef 2000–400 cm−1 employing KBr disc technique using Brukerermany make spectrometer model vertex-70.

.3.3. Raman spectroscopyThe room temperature Raman measurement on the powder

ample have been made by Jobin-Yovn Horiba Labram HR800 sin-le monochromator consisting of a single spectrograph (0.25 mocal length) containing a holographic grating filter (1800 grooves

m−1) and a Peltier-cooled CCD detector (1024 × 256 pixels of

Fig. 1. The Rietveld refined X-ray diffraction patterns for ZnxMn1 − xFe2O4 (x = 0.0,0.25, 0.5, 0.75, 1.0).

26 �m). The spectra were excited with 632.8 nm radiation (1.95 eV)from a 19 mW air-cooled He–Ne laser (Max Laser power: 19 mW).The laser beam was focused on the sample by a 50× lens to give aspot size of 1 �m. After each spectrum, a careful visual inspectionwas performed using white light illumination on the microscopestage in order to detect any change caused by the laser.

2.3.4. Mössbauer spectroscopyThe Mössbauer measurements were carried on powder samples

using a standard PC-based spectrometer equipped with a Weisselvelocity drive operating in the constant acceleration mode for thesite occupancy determination of the Fe, Mn, Zn ions. The Möss-bauer parameters were fitted by a standard least squares fittingprogram.

3. Results and discussion

Using co-precipitation technique the ZnxMn1 − xFe2O4 ferriteswere synthesized at 70 ◦C. The powder X-ray diffraction patternshave been collected on the surfaces of the disks with a Rigakudiffractometer using Cu K� radiation. Fig. 1 illustrates the rep-resentative �–2� scans of XRD for ZnxMn1 − xFe2O4 (x = 0.0, 0.25,0.5, 0.75, 1.0). The broad feature of XRD lines is an indicative ofnanosized ZnxMn1 − xFe2O4 ferrite and the pattern shows the exis-tence of single-phase cubic spinel structure. The data were furtherrefined by Rietveld method using the Fullprof program [16]. Allthe samples were fitted with space group (Fd3m), A-site Fe at(1/8, 1/8, 1/8), B-site Fe at (1/2, 1/2, 1/2) and O at (1/4 + u, 1/4 + u,1/4 + u) [17]. The parameters derived from the fit are illustrated inTable 1.

The refined occupancy at tetrahedral A site and octahedral B site

indicate that prepared ferrites are in the mixed state. Earlier, Rathand researchers [18] have reported that in addition to the ferritephase, XRD also documents hematite (�-Fe2O3) in MnFe2O4 andit is argued that the �-Fe2O3 phase might be due to preferential

D. Varshney et al. / Materials Chemistry and Physics 131 (2011) 413–419 415

Table 1Structural parameter for crystalline mixed ferrites ZnxMn1 − xFe2O4 obtained through Rietveld analysis with A site Fe at (1/8, 1/8, 1/8), B site Fe at (1/2, 1/2, 1/2) and O at(1/4 + u, 1/4 + u, 1/4 + u).

Composition (x) Lattice constant a (A) Atomic position x y z RBragg Rwp Rf �2 GOF index

0.0 8.486 Mn 0.158 0.158 0.158 15.8 23.0 10.1 3.49 1.90.25 8.476 Mn 0.254 0.254 0.254 13.3 22.4 8.2 3.34 1.8

Zn 0.108 0.108 0.1080.50 8.475 Mn 0.188 0.188 0.188 10.1 23.7 9.3 3.69 1.9

Zn 0.257 0.257 0.257000

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oss of one or more of the divalent cations during the precipitationrocess. They have prepared nanosize particles through hydrother-al precipitation route with a synthesis temperature of 180 ◦C andpH of 9, in the present case the pH 12 prevents the loss of one

f the divalent cations in ZnxMn1 − x Fe2O4 during co-precipitationrocessing.

The variation of lattice constant a in ZnxMn1 − xFe2O4 ferrites isound to be slightly less than that for the corresponding bulk val-es (≈8.5 A at x = 0) {Joint committee for powder diffraction (JCPD)ata} [19] consistent with the earlier measurements [18].

For ZnxMn1 − xFe2O4 doped ferrites, it is observed from Fig. 2 thathere is a decrease of lattice constant with increasing Zn2+ dopingoncentration, which can be understood on the basis of cation dis-ribution at both sites. The above variation is consistent with thearlier reported data [18]. The decrease in a with increased dop-ng concentration is attributed to the replacement of Mn2+ cationsaving a larger ionic radii (0.082 nm) by Zn2+ cations having amaller one (0.074 nm). It is worth to stress that in nano regimen2+ ions are randomly distributed between tetrahedral A and

ctahedral B sites, however Zn2+ ions have the highest tendencyo occupy the tetrahedral A site only. The partial oxidation of Mn2+

o Mn3+ and zinc loss let the lattice to contract in ZnxMn1 − xFe2O4anoparticles. It is worth to mention that all the samples haveeen prepared at a pH of 12 where the Zn2+ loss is minimum andhe oxidation of Mn2+ to Mn3+ is also ruled out in the presenttudy.

We have adopted Williamson–Hall approach for calculating therystallite size and strain contribution to the X-ray line broadening

ˇ1/2) in the present material, since Scherrer’s formula doesot take the strain contribution into account. According to thispproach, the X-ray line broadening is a sum of contribution from

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ig. 2. Variation of lattice parameter a as functions of doping concentration innxMn1 − xFe2O4 (x = 0.0, 0.25, 0.5, 0.75, 1.0).

.105 0.105 5.5 17.1 4.5 1.89 1.4

.256 0.256

.145 0.145 12.0 20.1 8.7 2.59 1.6

small crystallite size and the broadening caused by lattice strainpresent in the material [20], i.e.,

ˇ1/2 = ˇsize + ˇstrain (1)

where ˇsize = �/L cos � (from Scherrer’s formula) andˇstrain = 4� tan �; where � is the strain contribution. Thus, Eq.(1) becomes:

ˇ1/2 = �

L cos �+ 4� tan �

or

ˇ1/2 cos �

�= 1

L+ 4� sin �

�(2)

Hence, by plotting ˇ1/2 cos � versus sin � and by using the aboveexplained expression we can find the lattice strain and crystal-lite size. It is found that particle size gradually increases as theconcentration of Zn ion increases as shown in Fig. 3. The aboveis consistent with the measured X-ray diffraction pattern wherethe intensity of the most intense peak (3 1 1) slightly increases aswell the pattern seems narrower with enhanced Zn doping con-centration for ZnxMn1 − xFe2O4 [see Fig. 4]. The XRD 3 1 1 peak forZnFe2O4 is somewhat sharper as compared to MnFe2O4 indicating asteady growth in the crystallite size from 7.36 nm to 12.52 nm. Themechanism responsible for the increase in the particle diameter isattributed to coarsening phenomenon, which involves the growthof larger particles at the expense of smaller particles, this processis also known as Oswald ripening. However, Rath and coworkersreport that crystallite size of ZnxMn1 − xFe2O4 prepared at pH 9 with

a synthesis temperature of 180 ◦C decreases with increasing Zn2+

ion concentration [16].The porosity P of the ferrite nanoparticles was determined using

the relation P (%) = 1 − [d/dx] where, d is the apparent density and

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8

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Crystallite Size

Porosity (%)

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stal

lite

Size

(nm

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73

74

75

76

77

78

Concentration (x)

Porosity

Fig. 3. Variation of particle size and porosity as a function of doping concentrationin ZnxMn1 − xFe2O4 (x = 0.0, 0.25, 0.5, 0.75, 1.0).

416 D. Varshney et al. / Materials Chemistry and Physics 131 (2011) 413–419

383736353433

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ig. 4. Variation of (3 1 1) diffraction peak for ZnxMn1 − xFe2O4 (x = 0.0, 0.25, 0.5, 0.75,.0).

x is the X-ray density [21]. Fig. 3 shows that porosity decreasesrom 78.20% to 73.32% with the increase in Zn doping concen-ration and is attributed to the fact that the samples prepared byo-precipitation technique synthesized at 70 ◦C have dense randomacking.

The chemical and structural changes taking in a sample can bebserved from spectroscopic analysis. Fourier Transform Infraredpectroscopy (FT-IR) is one of the preferred methods of infraredpectroscopy. The transmission IR spectra of ZnxMn1 − xFe2O4anoparticles are shown in Fig. 5. It has been mentioned thatwo main broad metal–oxygen bands are seen in IR spectra ofll spinel ferrites [22]. The band around 600 cm−1 corresponds toibration of tetrahedral metal–oxygen [Fe–O] bond and the bandt 400 cm−1 to vibration of octahedral metal oxygen bond. Fur-hermore, the absorption band (in the range of 500–600 cm−1)orresponds to vibration of Fe2+–O2− bond of tetrahedral (A) site,hile a band around 1630 cm−1 assigned to the bending vibra-

ion of H2O absorbed after calcinations [23,24]. The IR spectrahow the band around 1384 cm−1 due to the presence of trappedO3− in the prepared ZnxMn1 − xFe2O4 series [25]. It is noticed

hat with enhanced Zn doping concentration in ZnxMn1 − xFe2O4,he peak corresponding to Fe–O bond becomes sharp and intense.his demonstrates the high degree of crystalline nature of ZnFe2O4anoparticles consistent with measured X-ray diffraction pattern.

Raman spectroscopy is a powerful probe to reveal the vibra-ional and structural properties of materials. Fe3O4 has a cubicnverse spinel structure of type AB2O4 that belongs to (Fd3m) spaceroup with eight formula units per unit cell. At room temperature

able 2aman active phonon mode of mixed ferrites ZnxMn1 − xFe2O4.

Raman active mode ZnxMn1 − xFe2O4 [Raman shift (cm−1)]

x = 0.0 x = 0.25

A1g 624.84 650.72T2g(3) – 511.77T2g(2) 390.86 402.31Eg 271.53 290.64T2g(1) 214.81 224.43

Fig. 5. FT-IR spectra of ZnxMn1 − xFe2O4 (x = 0.0, 0.25, 0.5, 0.75, 1.0) samples.

five Raman active (A1g + Eg + 3T2g) modes are observed as predictedaccording to group theory [10,26], which involve mainly the motionof the O ions and both the O and tetrahedral (A) site ions. Theanalysis based on quasi-molecular description of spinel structurecorresponds to the normal mode motions of FeO4 tetrahedron as:A1g is the symmetric stretch of oxygen atoms along Fe–O bonds,Eg and T2g(3) are the symmetric and asymmetric bends of oxygenwith respect to Fe, respectively, T2g(2) is the asymmetric stretch ofFe and O, and T2g(1) is the translatory motion of FeO4 as total [27].

Room temperature Raman spectrum of as synthesizedZnxMn1 − xFe2O4 ferrites in the frequency range of 150–750 cm−1

is shown in Fig. 6. On decomposing the fitted curves into individualLorentzian components, the natural frequency of each Ramanactive mode, was obtained in each of the sample. It has beenobserved that the introduction of Zn induces significant positivefrequency shift for all the phonon modes on moving from MnFe2O4to ZnFe2O4 that indicate the incorporation of Zn in the MnFe2O4lattice structure. The Raman modes of various samples are listedin Table 2. The T2g(1) mode (x = 0.0, 1.0) and T2g(3) mode (x = 0.5,0.75) for ZnxMn1 − xFe2O4 are unclear due to the broadening of linewidth for these ferrites. The Raman spectra of Zn0.25Mn0.75Fe2O4is quite different from the rest of the samples and showed ashoulder-like feature (around 608 cm−1) at lower wave numberside of A1g mode (∼650 cm−1). This doublet like feature has alsobeen observed in earlier reported data of NiFe2O4 [28]. This maybe due to the bond distribution, which probably results in thedoublet like structure. In Zn0.25Mn0.75Fe2O4, due to differences inthe ionic radii of Zn, Mn and Fe, the Fe/Zn–O and Fe/Mn–O bonddistances shows a considerable distribution. For MnFe2O4 exceptA1g mode, there is a systematic shift of 60–80 cm−1 as comparedto the earlier observed. We note that the synthetic sample used

had many defects and possibly, partial disorder [29].

It is worth to stress that band position of Raman mode is affectedby several factors such as strain and loss of symmetry. In case ofmixed ferrite nanocrystals where two or more divalent cation are

x = 0.5 x = 0.75 x = 1.0

661.90 663.46 664.97574.87 579.67 –470.72 482.18 487.40350.26 347.37 339.61

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D. Varshney et al. / Materials Chemistry and Physics 131 (2011) 413–419 417

200300400500600700

Inte

nsity

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Raman Shift (cm-1) Raman Shift (cm-1)

Raman Shift (cm-1) Raman Shift (cm-1)

Raman Shift (cm-1)

ZnFe2O4

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Inte

nsity

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Zn0.75Mn0.25Fe2O4

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Zn0.25Mn0.75Fe2O4

200300400500600700

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Zn0.5Mn0.5Fe2O4

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Fig. 6. Raman shift as a function of wave numb

nvolved, some disorder ness is created by induced strain whereasloss of symmetry could be brought about by many factors includ-

ng non-stoichiometry, presence of vacancies, lattice defect or byrdering of metal ions on their sites. The loss of symmetry leadso shifting of modes and broadening of line width. The modeseported for polycrystalline Mn0.62Zn0.30Fe2.08O4 ferrites with var-ous degrees of stress generated during the polishing process [30]nd for pure ZnFe2O4 at high pressures [31], although consistentut deviates slightly from the observed spectra in the present inves-igation.

Room temperature Mössbauer spectra of as synthesizednxMn1 − xFe2O4 series are represented in Fig. 7. The spectra are fit-ed with NORMOS-SITE program showing magnetic ordering. The

olid lines through the data points are the result of the computerts of the spectra on the basis of assumed line width for sextetnd doublet used for fitting. The spectrum with x = 0.0, was ana-yzed by considering two sextet and one doublet. The first sextet

ZnxMn1 − xFe2O4 (x = 0.0, 0.25, 0.50, 0.75, 1.0).

corresponding to a higher magnetic field is attributed to Fe3+ ionson the octahedral B-site and the other sextet corresponding tolower magnetic field is attributed to Fe3+ ions on the tetrahedralA-site.

The spectra with x = 0.25 was analyzed by one sextet and onedoublet. Furthermore, for higher doped samples (0.5 ≤ x ≤ 1.0), thespectra were analyzed using a single doublet and no six-line pat-tern was observed. The disappearance of sextet for higher doping inZnxMn1 − xFe2O4 is due to the fact that the magnetic domain sizesare small enough, and unable to trace a significant magnetic hyper-fine field to split the Mössbauer spectra into six distinct lines. Also,this might be due to the presence of non-magnetic Zn ion in theMnFe2O4 lattice. The six-line pattern observed in ZnxMn1 − xFe2O4

(x = 0.0 and 0.25) is due to superexchange interaction between themagnetic ions at tetrahedral and octahedral sublattices. The occur-rence of a doublet in ZnxMn1 − xFe2O4 (0.5 ≤ x ≤ 1.0) demonstratesthat the long-range magnetic ordering vanishes and particles

418 D. Varshney et al. / Materials Chemistry and Physics 131 (2011) 413–419

Table 3Mössbauer parameters of mixed ferrites ZnxMn1 − xFe2O4.

ZnxMn1 − xFe2O4 ı (mm s−1) �EQ (mm s−1) Hhf (T) Spectrum Assignment of site

x = 0.0 0.54 −0.21 49.00 6 B (Fe3+, Fe2+, Mn2+)0.48 0.75 – 2 A (Fe3+, Mn2+)

−1.00 −3.31 48.00 6 B (Fe3+, Fe2+)x = 0.25 0.30 −0.22 49.00 6 B (Fe3+, Mn2+, Fe2+)

0.29 0.93 – 2 A (Fe3+, Zn2+, Mn2+)x = 0.50 0.29 0.93 – 2 A (Fe3+, Mn2+, Zn2+)x = 0.75 0.29 0.93 – 2 A (Fe3+, Mn2+, Zn2+)x = 1.0 0.29 0.93

1050-5-10

X = 1.0

X = 0.75

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ig. 7. Room temperature Mössbauer spectra for ZnxMn1 − xFe2O4 (x = 0.0, 0.25, 0.50,.75, 1.0).

ehave like a single domain confirming the superparamagneticature.

The calculated values of the hyperfine parameters are listedn Table 3. We note that the deduced hyperfine parameters are

ith respect to natural iron matching with literature [32–34]. For= 0.50, 0.75 and 1.0, the value of isomer shift due to Fe3+ ion at Aite shows no significant change which indicates that the s electronensity at Fe3+ nucleus is not affected by the substitution of Zn ions.s nonmagnetic Zn2+ ions replaces Fe3+ ions at A site, and Mn2+ ionre randomly distributed at both the sites [4,35], the correct amountf Fe3+ present at A- and B-sites is estimated by determining therea under the Mössbauer absorption.

. Conclusions

In summary, a series of Mn, Zn doped Fe3O4 ferrites wereuccessfully prepared by the wet chemical technique with a tem-erature of 70 ◦C and a pH of 12. All the samples have beenharacterized by X-ray diffraction revealing single-phase crys-alline structure. The variation of lattice parameter with increasedn doping concentration illustrates a decreasing trend. The mixederrite crystallite size gradually increases with enhanced Zn dopingoncentration. Porosity shows decreasing trend with increased Znoping concentration and confirms that the synthesized samplesave dense random packing.

The absorption band at about 500–600 cm−1 in the IR spectra

orresponds to the vibration of Fe2+–O2− bond related to tetra-edral (A) site without any traces of impurity (NO3) peak. Slighteduction in bandwidth from MnFe2O4 to ZnFe2O4 shows thencreased in crystalline nature of ZnFe2O4 nanocrystals. Raman

[[[[

– 2 A (Fe3+, Zn2+)

spectroscopy revealed that phonon modes of all the samples arevery broad and shift toward the higher frequency site on replacingMn by Zn. Some of the modes for ZnxMn1 − xFe2O4 are unclear andcould not be distinguished properly due to the broadening of linewidth.

Room temperature Mössbauer spectra reveals that spectra forMnFe2O4 shall be analyzed consistently by two sextet and one dou-blet whereas the spectra with x = 0.25 was analyzed by one sextetand one doublet. For ZnxMn1 − xFe2O4 (0.5 ≤ x ≤ 1.0), the spectrawas analyzed using a one doublet without any sextet and is dueto the presence of non-magnetic Zn ion.

Acknowledgements

Authors are thankful to UGC-DAE CSR, Indore for providingcharacterization facilities. Financial assistance from UGC-DAE CSR,Indore is gratefully acknowledged. Author K. Verma extends hisappreciation to UGC, New Delhi, India for Rajiv Gandhi NationalFellowship (RGNF).

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