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Journal of Alloys and Compounds 646 (2015) 550e556

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Journal of Alloys and Compounds

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Distribution of cations in Co1�xMnxFe2O4 using XRD, magnetizationand M€ossbauer spectroscopy

S.P. Yadav a, d, S.S. Shinde a, b, Pramod Bhatt c, S.S. Meena c, K.Y. Rajpure a, *

a Electrochemical Materials Laboratory, Department of Physics, Shivaji University, Kolhapur 416 004, Indiab Hanynag University, Ansan, Republic of Koreac Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400 085, Indiad Modern college, Vashi, Navi Mumbai, India

a r t i c l e i n f o

Article history:Received 6 April 2015Received in revised form11 May 2015Accepted 24 May 2015Available online 20 June 2015

Keywords:Cation distributionCo1�xMnxFe2O4 ferriteM€ossbauer spectraHyperfine splitting

* Corresponding author.E-mail address: rajpure@yahoo.com (K.Y. Rajpure)

http://dx.doi.org/10.1016/j.jallcom.2015.05.2700925-8388/© 2015 Elsevier B.V. All rights reserved.

a b s t r a c t

The nanocrystalline Co1�xMnxFe2O4 (0 � x � 0.5) ferrites are synthesized by auto-combustion method.The structural properties and phase identification of the samples are studied using X-ray powderdiffraction and the Rietveld analysis. The refinement results confirm that the cationic distribution overthe tetrahedral and octahedral sites in the spinel lattice is partially inverse. The magnetic properties ofthe prepared samples are studied by using an MeH hysteresis curves. The maximum saturationmagnetization and coercivity of samples are 68.94 emu/gm and 1.59 KOe respectively. From 57FeM€ossbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting and hy-perfine magnetic field on Mn2þ substitution have been studied. The composition dependent cationdistribution estimated from Rietveld analysis and magnetic studies is in good agreement with each other.

© 2015 Elsevier B.V. All rights reserved.

1. Introduction

The preparation of ferrite materials has received much attentiondue to their significant importance to the electronic industries [1,2].Cobalt ferrite (CoFe2O4) is a ferrimagnetic material which presentsthe highest magnetocrystalline anisotropy (K1 ¼ þ2 �106 erg cm�3) with three axes [100] and magnetostriction coeffi-cient (250 ppm) among all ferrites [3]. It has been regarded as oneof the competitive candidates for variety of applications in micro-wave devices, high sensitivity sensor, high density magneticrecording media and biomedical industries [4,5]. CoFe2O4 has beenan inverse spinel cubic crystal structure in which half of thetetrahedral sites (A-sites) are occupied by half of Fe3þ ions. Theoctahedral sites (B-sites) will be held by the leftover Fe3þ with thetransition metal ions. It is known fact that the addition of suitabletransition metal ion into the spinel structure creates movement ofmany cations between existing two lattice sites and directly affectson the magnetic properties. Incorporation of a relatively smallamount of manganese shows an important modification in thestructural, magnetic and electrical properties. The magnetic prop-erties of the ferromagnetic oxides are largely governed by the

.

FeeFe interaction (the spin coupling of the 3d electrons) and byintroducing Mn ions into the spinel lattice, the MneFe interactionsstarts to have an appreciable effect (3de3d coupling), which leadsto change in the cation distribution, magnetization and Curietemperature. The properties of ferrites depend mainly on thetechnique and conditions of preparation, which in turn affect thecation distribution over the tetrahedral Aesite and the octahedralBesite. Epifani et al. [6] studied the critical role of metal cationsdistribution in the metal ferrites. Atif et al. reported [7] the effect ofMn substitution on temperature dependent magnetic properties ofMn substituted cobalt ferrite.

In the presentwork, properties of chemically preparedmagneticnanoparticles of CoFe2O4 are modified byMn substitution due to itsintrinsic magnetic moment and anisotropy. In such a case, therotation of the spin is largely controlled by the crystalline field ef-fect of doped ions and if this anisotropy field is strong enough, thespins are forced to align along the local anisotropic axis. In order tostudy the relative site preference of Mn2þ, Co2þ and Fe3þ fortetrahedral and octahedral sites in spinel lattice, the solid solutionseries Co1�xMnxFe2O4 (0 � x � 0.5) has been prepared. The cationdistributions have been determined through X-ray diffraction andconfirmed by magnetization and M€ossbauer measurements. Thevariation in isomer shift, hyperfine and quadruple splitting havebeen studied with Mn substitution.

S.P. Yadav et al. / Journal of Alloys and Compounds 646 (2015) 550e556 551

2. Experimental

The Co1�xMnxFe2O4 (0 � x � 0.5) samples were prepared by theauto-combustion route using equimolar ferric nitrate, cobalt nitrateand manganese nitrate of s. d. fine Ltd., Mumbai with 98.6, 99 and98.6% respective purities as precursors. A mixture of precursors inatomic proportion (stoichiometric) was taken into a Pyrex dish andmelted by heating at 80

�C. Then appropriate amount of fuel glycine

was added in the mixture. The equivalence ratio, Fe (O/F) of theredox mixture for the combustion is calculated by using the totaloxidizing and reducing valencies of the oxidizer (O) and of the fuel(F), which serve as numerical coefficients so thatFe, becomes unityand the heat released is at its maximum [5]. According to theprinciples used in propellant chemistry, the oxidizing and reducingvalencies of various elements are considered as follows: C ¼ 4,H ¼ 1, O ¼ �2, N ¼ 0, M ¼ 2, 3, etc. Thus, typically for ferrites i.e.M2þFe3þ2 O4 the oxidizing valency of a divalent metal nitrate,M(NO3)2 becomes �10; for trivalent Fe(NO3)3, it is �15, whichshould be balanced by the total valences in the fuel; glycine(H2NCH2COOH), which add up to þ9. Hence for the stoichiometriccomposition of the redoxmixture, in order to release themaximumenergy for the reaction, require that �40þ 9n ¼ 0 or n ¼ 4.44 molof glycine. After evaporation of the water content, the mixtureignited to combust with a flame, giving voluminous and foamysamples. The synthesized powder was annealed at 1000

�C for 12 h.

The used synthesis process i.e., auto combustion have various ad-vantages such as simple, inexpensive, quick synthesis, does notrequired any vacuum process or sophisticated instrumentation,easy growth of nanoparticles and environmental friendly.

The structural properties were studied by a Rikagu Miniflex (II)(l, 1.5406 Å) X-ray diffractometer using Cu-Ka radiation in the spanof 20e65�. All the X-ray diffraction (XRD) patterns were analyzedwith the help of FullProf programme by employing Rietveldrefinement technique. The XRD patterns for all the samples couldbe refined using the F d 3 m space group. Initially, the global pa-rameters viz. background and scale factors were refined. In the nextstep, the structural parameters viz. lattice parameters, profileshape, width parameters, preferred orientation, asymmetry,isothermal parameters, atomic coordinates, and site occupancieswere refined. The quality of fitting of the experimental data wasassessed by calculating the parameters such as the ‘goodness of fit’c2 and the R factors (Rp the profile factor, RB the Bragg factor, and RFthe crystallographic factor). Magnetic properties were studied us-ing hysteresis loop tracer (Magneta BeH loops tracer) at amaximum applied field of 6.5 KOe. M€ossbauer spectra have beenobtained using a spectrometer (Nucleonix Systems Pvt. Ltd.) oper-ated in constant acceleration mode (triangular wave) in trans-mission geometry. The source employed was Co-57 in Rh matrix ofstrength 50 mCi. The calibration of the velocity scale is done byusing a a-Fe metal foil. The inner line width of calibration spectra is0.23 mm/s. M€ossbauer spectra were fitted by a least square fit(MOSFIT) programme assuming Lorentzian line shapes.

3. Results and discussion

3.1. Structural analysis

The XRD patterns along with Rietveld refined data for theCo1�xMnxFe2O4 ferrites have been shown in Fig. 1. The experi-mental data are shown as open circles, and calculated intensitiesare shown as solid lines. The difference between the measured andthe calculated intensities is shown by bottom line. The allowedBraggs positions for the F d 3 m (No.: 227) space group are markedas vertical lines. The existence of the (220), (311), (222), (400),(422), (333)/(511) and (440) major lattice planes in the Rietveld

refined XRD patterns confirms the formation of single phase mixedcubic spinel structure preserving the F d 3 m space group. Peaksshifting towards lower angle (2q) with Co substitution (from 35.52for x ¼ 0.0 to 35.34� for x ¼ 0.5) have been observed. In therefinement, the oxygen positions (x¼ y¼ z) have been taken as freeparameters. However, all other atomic fractional positions havebeen taken as fixed. Other parameters such as lattice constants,isothermal parameters, occupancies, scale factors, and shape pa-rameters have been taken as free parameters. The background wascorrected by pseudo-Voigt function. Typical atomic coordinate (x, y,z) and occupancies of different atoms for Co1�xMnxFe2O4 samplesare given in Table 1.

The various R factors for Reitveld profile fitting are specified inTable 2. Relatively higher values of R factor viz. Rp results due tonanocrystalline nature of the material and could be assigned to thelarger signal-to-noise ratio. However, a low value of c2 (goodness offit) have been observed which supports the goodness of refine-ment. Variation of (311) peak shift, lattice constant and oxygenposition parameter obtained from Rietveld refinement are shownin Fig. 2. It is observed that the lattice constant increased with Co2þ

substitution obeying Vegard's law. The increasing trend in the lat-tice parameter is attributed to the replacement of Co2þ (0.78 Å) ionsby the larger Mn2þ (0.83 Å) ions [8], in the host system [9]. How-ever, the position of (311) peak is slightly shifted toward lowerangle (Fig. 2 a & b) due to fact that atomic radius of Mn is greaterthan Co and smaller than Fe.

Variation of crystallite size, calculated by Scherer's formula, withcomposition is shown in Fig. 3. It is observed that crystallite sizedecreases with the increase of composition after slight initial in-crease. It is due to the restricted growth of the crystal with theincrease of x. The crystallite size is related to the relative interde-pendence between the nucleation and growth steps, and it isstrongly affected by the synthesis route which gives different ratesof ferrite formation [10,11].

The cation distribution was determined using the Rietveldrefinement of the occupancy values. The site occupancy analysis fortypical Co0.9Mn0.1Fe2O4 sample reveals that 4% tetrahedral siteshave been occupied by the Co ions, 8% tetrahedral sites have beenoccupied by theMn ions and the remaining 88% tetrahedral sites byFe ions. Hence, the chemical formula for this sample is (Fe0.88Co0.04Mn0.08)[ Fe1.12Co0.86 Mn0.02]O4, where cations in round and squarebracket occupy the tetrahedral and octahedral sites, respectively.Similar kind of cation distribution is reported by Ammar et al. [12].The estimated cation distributions are listed in Table 3. It isobserved that Co ions are present on both tetrahedral and octa-hedral sites, which reveals that the samples are in mixed spinelstructure irrespective of the composition. As the composition isincreased, there is a redistribution of cation within the octahedralsite. This change of cation distribution is consistent with the changeof lattice constant. In bulk cobalt ferrite material, the Co2þ ionshows a strong preference for octahedral site (B site) [13]. Here, weobserved that Co2þ ion occupies both the tetrahedral (A site) andoctahedral sites (B site).

3.2. Magnetic measurements

The substitution of Mn ions, which is having a preferential A-and B-site occupancies respectively, results in the reduction of theexchange interaction between A- and B-sites. Hence, by varying thedegree of Mn substitution, the magnetic properties of the nano-particles can be varied. Fig. 4 shows the room temperature(300 K) hysteresis loops of nanocrystalline Co1�xMnxFe2O4 ferritesystem (x ¼ 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5).

The values of saturation magnetization (MS), coercivity (HC),remanent magnetization (Mr), magnetic moment (mB) and

Fig. 1. Rietveld refined X-ray diffraction patterns of Co1�xMnxFe2O4 samples.

S.P. Yadav et al. / Journal of Alloys and Compounds 646 (2015) 550e556552

proposed cation distribution from magnetic measurements havebeen listed in Table 4. The saturation magnetization ofCo1�xMnxFe2O4 increases up to x ¼ 0.3 and then decrease at higherconcentration. The coercivity decreases (1592e604 Oe) with Mnsubstitution. The magnetic moment per formula unit in Bohrmagneton is calculated using formula,

mB ¼ W �Ms5585

(1)

where mB is the magnetic moment of the samples in Bohr

Table 1Typical atomic coordinates (x, y, z) and occupancy of different atoms forCo1�xMnxFe2O4 samples.

Atoms Coordinate Occupancy

x y z 0 0.1 0.2 0.3 0.4 0.5

Fe (8a) 0.125 0.125 0.125 0.96 0.88 0.80 0.72 0.64 0.56Co (8a) 0.125 0.125 0.125 0.04 0.04 0.04 0.04 0.04 0.04Mn (8a) 0.125 0.125 0.125 0.0 0.08 0.16 0.24 0.32 0.4Mn (16d) 0.5 0.5 0.5 0.0 0.02 0.04 0.06 0.08 0.1Fe (16d) 0.5 0.5 0.5 1.04 1.12 1.20 1.28 1.36 1.44Co (16d) 0.5 0.5 0.5 0.96 0.86 0.76 0.66 0.56 0.46O (32e) e e e 4 4 4 4 4 4

magneton, MS is the saturation magnetization and W is the mo-lecular weight of the sample [14]. In spinel ferrites the magneticproperties depend on the sum of the magnetic moments at tetra-hedral -A site and octahedral -B site [15]. The magnetic momentvalue in terms of Bohr magneton increases from 3 to 4 with Mnsubstitution. It is seen that the substituted Mn ions are occupied onoctahedral B sitewith decreasing concentration of Co ions on B-site.

3.3. M€ossbauer spectroscopy

The 57Fe M€ossbauer spectra of Mn substituted cobalt ferrite(Co1�xMnxFe2O4), recorded at room temperature are shown inFig. 5. The symbols signify the experimental data and the contin-uous lines corresponding to least-squares fits. The data on chemicalisomer shifts, quadrupole splitting and hyperfine magnetic fields,coupled with intensity measurements provide a powerful means ofstudying site occupancy and site symmetry [16]. VariousM€ossbauer parameters calculated from the fitting of the spectra aretabulated in Table 5. The M€ossbauer spectrum for CoFe2O4

(composition x ¼ 0) was fitted to a double sextuplet pattern, whichwas attributed to Fe3þ at the tetrahedral (A) and octahedral (B)coordination sites in the spinel crystal structure, and doublet rep-resenting the paramagnetic behavior of the nano-particles. Ac-cording to the fitting parameters, the outer sextuplet with the large

Table 2Data on Rietveld agreement factors, lattice constant, unit cell volume and oxygen position parameter of Co1�xMnxFe2O4 samples.

Reitveld factors Composition (x)

0 0.1 0.2 0.3 0.4 0.5

Rp (%) 16.3 14.6 15.6 12.2 14.5 12.6RB (%) 5.30 2.57 3.01 3.86 3.32 3.92Rwp (%) 22.7 22.3 23.3 17.6 20.8 18.2RF (%) 4.28 2.51 2.71 3.18 2.89 3.63c2 1.22 1.21 1.23 1.12 1.12 1.11a (Å) 8.3754 8.3919 8.4024 8.4165 8.4193 8.4281a* (Å) 0.1193 0.1192 0.1190 0.1188 0.1187 0.1186V (Å3) 587.52 590.99 593.22 596.21 596.79 598.66O (x ¼ y ¼ z) 0.25376 0.25587 0.25559 0.25465 0.25616 0.25686

S.P. Yadav et al. / Journal of Alloys and Compounds 646 (2015) 550e556 553

hyperfine field (50.67 T), and isomer shift (0.5346 mm/s), corre-sponds to the Fe3þ/Fe3þ ions occupying the octahedral B-sites,while the other sextuplet with the smaller center shift (0.2285mm/s) is attributed to the Fe3þ ions at tetrahedral A-sites.

For x > 0, M€ossbauer spectra were fitted into multiple sextupletpatterns and doublets. While assigning the site occupancyfollowing observations were assumed: chemical isomer shift in-creases in the sequence d (tetrahedral Fe3þ) < d (octahedralFe3þ) < d (tetrahedral Fe2þ) < d (octahedral Fe2þ) and the magnetichyperfine field at Fe2þ is less than at Fe3þ. CoFe2O4 is basically aninverse Fe3þ spinel, with the A and B site hyperfine field averages tobe 51.6 T [17,18]. Inverse Fe3þ spinel nature is clearly evidencedfrom the relative area data of two setuplets. Further nano-particleCoFe2O4 shows superparamagnetic behavior with partial collapseof the hyperfine spectrum at temperatures below the Neel

Fig. 2. (311) peak position (a, b), lattice constant (b), oxygen position paramete

temperature [19]. MnFe2O4 is partly inverse [20], therefore thedegree of inversion of Co ferrite decreases with increasing the Mncontent. Inconsistencies in the published data for MnFe2O4 havebeen suggested to result from non-stoichiometry with oxygen va-cancies and Fe2þ cations [21].

The variation in M€ossbauer parameters; such as isomer shift (d),quadruple splitting (D), line width (G), hyperfine field (Hfb) andrelative area (RA), with Mn substitution determined from the fittedsub patterns are shown in Fig. 6(aee, respectively). The chemicalisomer shift occurs due to the change in nuclear radius anddiffering chemical environments and is related to the formaloxidation state of the iron at tetrahedral (A) and octahedral (B)sites. The observed values of d show an irregular change withsubstitution of Co. d for Fe2þ at A site and Fe3þ at B site decreaseswhile for Fe3þ at A site increases with Mn substitution (Fig. 6a). It

r (c) variation with respect to composition (x) for Co1�xMnxFe2O4 samples.

Fig. 3. Variation of crystallite size with respect to composition (x) for Co1�xMnxFe2O4

samples.

Table 3Site occupancies of cations for Co1�xMnxFe2O4 samples.

Composition, x Cation distribution

Tetrahedral (A) site Octahedral (B) site

0.00 (Fe0.96 Co0.04) [Fe1.04 Co0.96]0.10 (Fe0.88 Co0.04 Mn0.08) [Mn0.02Fe1.12 Co0.86]0.20 (Fe0.80 Co0.04 Mn0.16) [Mn0.04Fe1.20 Co0.76]0.30 (Fe0.72 Co0.04 Mn0.24) [Mn0.06Fe1.28 Co0.66]0.40 (Fe0.64 Co0.04 Mn0.32) [Mn0.08Fe1.66 Co0.56]0.50 (Fe0.56 Co0.04 Mn0.4) [Mn0.1Fe1.44 Co0.46]

Fig. 4. Variation of magnetization with applied field for Co1�xMnxFe2O4 samples.

S.P. Yadav et al. / Journal of Alloys and Compounds 646 (2015) 550e556554

implies that the s-electron charge density of Fe3þ ions has influ-enced by Mn substitution. It is examined that d values for octahe-dral sites are greater than that for tetrahedral sites [22]. The

Table 4Variation of magnetic properties of Co1�xMnxFe2O4 samples.

Composition(x)

MS (emu/gm)

Coercivity HC (Oe) Magnetic Moment mB (Bohr magneton

0.0 52.55 1592 2.200.1 58.54 1303 2.450.2 64.77 1051 2.710.3 68.94 821 2.880.4 65.55 735 2.730.5 57.26 604 2.38

variation in quadruple splitting, D (Fig. 6b) for observed compo-nents with respect to composition are negligible (except fordoublet). This is attributed to the fact that overall cubic symmetry ismaintained between Fe3þ ions and their surroundings with thesubstituted Mn2þ ions. Ferrous (Fe2þ) ions usually have a non-cubicenvironment and give a large quadrupole splitting in paramagneticcomplexes.

In ferrites, the doublet structure of M€ossbauer spectra arisesfrom the quadrupole interaction of 57Fe nuclei with the electricfield gradient located at octahedral sites. The electric field gradientarises due to the non-spherical distribution of the 3d electrons ofthe cation and the effective charge on the neighboring ions [23]. ForFe2þ which has a non-spherical distribution of the 3d electrons, theelectric field gradient arises in this way. Line width (G) varies be-tween 0.3 and 0.7 mm/s and there is meagre variation in line widthof Fe3þ components at A site (Fig. 6c) possibly due to slight varia-tions in the spin-lattice relaxation times with respect to Mnsubstitution.

The magnetic hyperfine field arises mainly from three differentbases: the first is the polarization of seelectrons by the magneticmoments of the deelectrons; the second is the dipolar fields of thesurrounding magnetic ions and their distribution in Ae andBesites; and the third is the super transferred hyperfine fieldsarising from the magnetic moments of nearest neighboring cations[24]. The variation in hyperfinemagnetic field of different sextets asa function of Mn substitutions is given in Fig. 6d. It is observed thathyperfine field decreased with increasing Mn substitution and thiscan be qualitatively explained using Neel's super exchange in-teractions [25]. In CoeMn ferrite, as both A and B sites are occupiedby Fe3þ and Fe2þ ions, so the interaction of these ions are possiblewith Co2þ and Mn2þ ions. In the present series Co2þ ions withmagnetic moment 3 mB are substituted by Mn2þ ions with a mag-netic moment of 5 mB [26]. This should result into increase ofmagnetic linkages in Fe3þA � O� Fe3þB , Fe3þA � O�Mn2þ

A and Fe3þA �O� Co2þA leading to increase in hyperfine field. The decrease ofhyperfine field with increasing of Mn content indicates that Mn2þ

ions are distributed over either Ae or Besite. The distribution of Feion over Ae and Besites is proportional to the relative area of Aeand Be M€ossbauer sub-spectra (Fig. 6e). The proposed cation dis-tribution estimated using the relative area of the components fromM€ossbauer studies is in good agreement with that estimated fromXRD and magnetic measurements.

4. Conclusions

Nanocrystalline Co1�xMnxFe2O4 ferrite synthesis using auto-combustion method is feasible. Structural analysis with Rietvieldrefinement confirms the formation of single phase cubic inversespinel structure of CoeMn ferrite. Cation distribution estimatedfrom XRD, magnetic and M€ossbauer studies show that the Mn2þ

ions show their preference towards octahedral B site, whereas Fe3þ

and Co2þ ions are randomly distributed over A- and B-site.M€ossbauer spectra show that there is a significant change in the

) Magnetic Moment mB Cation distribution Cation distribution

Tetrahedral (A) site Octahedral (B) site

3 (Fe1.0) [Fe1.0 Co1.0]3.2 (Fe0.9 Mn0.1) [Fe1.1 Co0.9]3.4 (Fe0.8 Mn0.2) [Fe1.2 Co0.8]3.6 (Fe0.7 Mn0.3) [Fe1.3 Co0.7]3.8 (Fe0.6 Mn0.4) [Fe1.4 Co0.6]4 (Fe0.5 Mn0.5) [Fe1.5 Co0.5]

Fig. 5. 57Fe-M€ossbauer spectra for Co1�xMnxFe2O4 (0 � x � 0.5).

Table 557Fe-M€ossbauer parameters for Co1�xMnxFe2O4 (0� x� 0.5): BHf is themagnetic hyperfine field at 57Fe nuclei, d is the isomer shift relative to a-Fe foil,D is the quadrupole shift,and G is the line width at half maximum.

Mn content (x) Iron sites G (mm/s) d (mm/s) D (mm/s) BHf (Tesla) Relative area RA (%) Site occupancy

0.0 Sextet 1 0.2864 0.226 �0.0399 49.85 71.0 A: Fe3þ

Sextet 2 0.5079 0.5339 0.027 50.659 25 B: Fe3þ,Fe2þ

Doublet e 0.5145 0.337 0.7798 4 B: Fe3þ,Fe2þ

0.1 Sextet 1 0.367 0.252 �0.044 49.16 69.9 A: Fe3þ

Sextet 2 0.603 0.508 0.0726 49.85 28.6 B: Fe3þ,Fe2þ

Doublet e 0.501 0.398 0.856 2.5 B: Fe3þ,Fe2þ

0.2 Sextet 1 0.397 0.249 �0.008 49.17 65.0 A: Fe3þ

Sextet 2 0.636 0.283 �0.035 47.21 32.4 B: Fe3þ

Doublet e 0.502 0.298 0.784 2.6 B: Fe3þ,Fe2þ

0.3 Sextet 1 0.3508 0.247 0.0067 48.78 57.9 A: Fe3þ

Sextet 2 0.6958 0.3424 �0.1151 45.3851 38.1 B: Fe3þ

Doublet e 0.518 0.358 0.7839 4.0 B: Fe3þ,Fe2þ

0.4 Sextet 1 0.3122 0.2971 0.0086 48.58 42.4 A: Fe3þ

Sextet 2 0.7106 0.3624 �0.0123 45.686 51.8 B: Fe3þ

Doublet e 0.622 0.4081 0.9564 5.8 B: Fe3þ,Fe2þ

0.5 Sextet 1 0.3448 0.3011 0.0043 48.443 46.2 A: Fe3þ

Sextet 2 0.7003 0.3752 �0.035 45.2882 50.1 B: Fe3þ

Doublet e 0.5829 0.4121 0.876 3.7 B: Fe3þ,Fe2þ

S.P. Yadav et al. / Journal of Alloys and Compounds 646 (2015) 550e556 555

Fig. 6. Variation in isomer shift (d), quadrupole splinting (D), Line width (G), hyperfine magnetic fields (Bhf) and relative area (RA) of tetrahedral and octahedral sites with Mnsubstitution in Co1�xMnxFe2O4 system.

S.P. Yadav et al. / Journal of Alloys and Compounds 646 (2015) 550e556556

values of isomer shift. The hyperfine magnetic field at both the sublattices decreased with the introduction of Mn2þ ions by weak-ening of the coupling bonds between Fe3þA � O� Fe3þB sourceinteractions.

Acknowledgment

This work is partly supported by UGC through financial supportthrough its project No. 41-869/2012 and CSIR through project No.03(1284)/13/EMR-II.

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