STRUCTURAL PROPERTIES AND CATION DISTRIBUTION OF Co–Zn NANOFERRITES

December 9, 2009 11:48 WSPC/INSTRUCTION FILE S021797920905225X

International Journal of Modern Physics BVol. 23, No. 30 (2009) 5629–5638c© World Scientific Publishing CompanyDOI: 10.1142/S021797920905225X

STRUCTURAL PROPERTIES AND CATION DISTRIBUTION

OF Co–Zn NANOFERRITES

SANTOSH S. JADHAV∗, SAGAR E. SHIRSATH†, B. G. TOKSHA†, S. M. PATANGE†,S. J. SHUKLA‡ and K. M. JADHAV†

∗D.S.M.’s Arts, Commerce and Science College, Jintur 431 509, M.S., India†Department of Physics, Dr. Babasaheb Ambedkar Marathwada University,

Aurangabad 431001, M.S., India‡P.G. and Research Centre, Department of Physics, Deogiri College,

Aurangabad, M.S., India∗[email protected]

Received 12 June 2008

The soft spinel ferrite system having the general formula Co1−xZnxFe2O4 with x vary-ing from 0.0 to 0.7 has been prepared by wet-chemical co-precipitation technique. Theprepared samples were characterized by XRD technique. The analysis of XRD patternrevealed the formation of single-phase cubic spinel structure. The Bragg peaks in XRDpattern are broader indicating fine particle nature of the sample. XRD data have beenused to study structural parameter and cationic distribution in Co–Zn ferrite. The parti-cle size is of nanometer dimension. Cation distribution results suggest that Co2+ occupyB-site, Zn2+ occupy A-site, and Fe3+ occupy both the A- and B-site.

Keywords: Soft ferrites; X-ray diffraction; cation distribution.

PACS numbers: 75.50.Gg, 75.75.+a, 61.10.Nz

1. Introduction

Ferrites are important components in the latest electronic products, such as cell

phone, computers, video cameras, etc. They acquire small dimension and light

weights and have better functions at nanoscale. Soft ferrites are of great inter-

est because of their high initial permeability over a large frequency range leading

to widespread applications, e.g., inductor cores in RF system, recording heads, and

microwave devices. Soft ferrites are commercially important materials because of

their excellent magnetic and electrical properties.1

The frustrated magnetic structure in ferrite with the spinel structure can arise

when there is a replacement of magnetic ions by nonmagnetic ones.2,3 The frustra-

tion is necessary condition for the appearance of a canted local state, which was first

∗Corresponding author.

5629

http://dx.doi.org/10.1142/S021797920905225X


5630 S. S. Jadhav et al.

obtained by Deniels and Rossenweig.4 Ferrite (MFe2O4, M = Co2+, Ni2+, Fe2+,

Zn2+, Cu2+, etc.) nanocrystals attract great research interest due to their poten-

tial application in ferrofluids,5–7 magnetic fluids,8 magnetic recording media,9 and

magnetic resonance image10 for e.g., CoFe2O4 has a high coercivity (5400 Oe) and

moderate saturation magnetization (∼80 emug−1), a remarkable chemical stabil-

ity, and a mechanical hardness, which make it possible material for high density

recording media.11,12 The effects of Zn substitution on the properties of Co and

Mn ferrite have been studied by Arulmurugan et al.13 and it was concluded that

preparation conditions completely favor the formation of ferrites.

It has been reported that the properties of nanosize dimension ferrite system and

its bulk counter part are altogether different.14 The properties exhibited by nanosize

spinel ferrite are found to be superior. Keeping in view the importance of nanosize

ferrite, we have synthesized Co1−xZnxFe2O4 spinel ferrite system by wet-chemical

co-precipitation method and their physical properties have been investigated. In the

present paper, we report our results on the physical properties of nanosize Co–Zn

spinel ferrite.

2. Experimental Method

In the present work, Co1−xZnxFe2O4 soft ferrite samples with composition x = 0.0–

0.7 were synthesized by wet-chemical co-precipitation method. The samples were

prepared by air oxidation of an aqueous suspension containing Co2+, Zn2+ and Fe3+

cations in proper proportions. The starting solutions were prepared by mixing 50ml

of aqueous solution of FeSO4 · 7H2O, CoSO4 · 7H2O and ZnSO4 · 7H2O (all 99.9%

pure supplied by s.d. fine, India) in stoichiometric proportions. A two molar (2 M)

solution of NaOH was prepared as a precipitant. In order to achieve simultaneous

precipitation of all the hydroxides Co(OH)2, Zn(OH)2, and Fe(OH)2, the starting

solution (pH ≈ 3) was added to the solution of NaOH and a suspension (pH =

11) containing dark intermediate precipitates was found. Then the suspension was

heated and kept at a temperature of 60◦C, while oxygen gas was bubbled uniformly

into the suspension to stir it and to promote the oxidation reaction, until all the

intermediate precipitates changed into the dark brownish precipitates of the soft

ferrite. The samples were filtered, washed several times by distilled water. The

formation of wet-chemically prepared Zn-substituted cobalt ferrite using chlorides

as starting materials is reported in the literature wherein the sintering temperature

is about 700◦C.13,15 From these data, the wet samples in the present Co–Zn system

were annealed at 725◦C for 16 h.

The X-ray powder diffraction patterns of powder samples were recorded on

Philips X-ray diffractometer (PW 3710) having Ni filter and Cu-Kα radiation with

wavelength 1.5406 A. The XRD patterns were in the 2θ range of 20◦ to 80◦ with

scanning rate 1◦/min. The structural parameters such as particle size, lattice con-

stant were derived from XRD patterns and other physical parameters such as bond

lengths, X-ray density, hopping length were also derived.


Cation Distribution of Co–Zn Nanoferrites 5631

The XRD line width and particle size are calculated through the Scherrer

equation:

t =0.9λ

B cos θB

, (1)

where t is the diameter of crystal particle, λ is the wavelength of the X-ray radiation,

θB is Bragg’s angle, B is the measure of broadening of diffraction due to size effect.

The bond lengths on tetrahedral (A) site (shortest distance between A-site

cation and oxygen ion) and octahedral [B] site (shortest distance between B-site

cation and oxygen ion) can be calculated. The values of tetrahedral and octahedral

bond length dAX and dBX, tetrahedral edge, shared and unshared octahedral edge

(dAXE, dBXE, and dBXEU) can be calculated by putting the experimental values of

lattice parameter “a” and oxygen positional parameter “u” of each sample in the

following equations16:

dAX =

(

u − 1

4

)

a√

3 (tet. bond) , (2)

dBX = a ×√

(

3u2 − 11

4u +

43

64

)

(oct. bond) . (3)

The lattice edges on both tetrahedral (A) site and octahedral [B] site can be

computed from the relations:

dAE =

(

2u− 1

2

)

a√

2 (tet. edge), (4)

(dBE)shared = (1 − 2u)a√

2 (shared octa. edge), (5)

(dBE)unshared = a ×√

(

4u2 − 3u +11

16

)

(unshared octa. edge). (6)

The pellets in cylindrical shape were prepared using a die having bore radius

0.6mm. The pressure of 6 ton was applied on the powder. Polyvinyl alcohol (2 wt%)

was added as a binder. The measured density dm was determined using the for-

mula,17

dm =m

πr2h(7)

where m is the mass, r is the radius, and h is the height of the pellet.

The X-ray density of all the samples of the series Co1−xZnxFe2O4 has been

calculated from the molecular weight and the volume of the unit cell using the

formula,18:

dx =8M

Na3gm/cm

3(8)

where M is the molecular weight, N is Avogadro’s number, and a is the lattice

parameter.



The porosity “P” of the ferrite nanoparticles was then determined using the

relation,17

P = 1 − dm

dx

, (9)

where dm and dx are the measured densities and X-ray densities, respectively.

The specific surface area was calculated from the measured diameter of the

particle and density of the sample using the relation19

S =6000

tdm

. (10)

3. Results and Discussion

Figure 1 depicts the X-ray diffraction (XRD) patterns of the typical compositions

x = 0.3, 0.5, and 0.7 of the series Co1−xZnxFe2O4. The formation of single phase of

20 30 40 50 60 70 80

2 θ (degree)

Inte

nsi

ty(a

rb.

unit

)

x = 0.3

x = 0.5

x = 0.7

(220)

(311)

(222)

(400

)

(422) (3

33)

(440

)

(620

)

(622

)

Fig. 1. XRD patterns for the samples x = 0.3, 0.5, and 0.7 of the series Co1−xZnxFe2O4.



Co–Zn ferrites was concluded from the XRD patterns of the investigated samples.

All diffraction peaks are indexed to a pure cubic spinel phase. The lattice parameter

“a” was calculated using the equation

a = d√

(h2 + K2 + l2) , (11)

where d is the interplanar spacing and (hkl) is the index of the XRD reflection

peak. For an accurate calculation of lattice constant “a” lattice parameter for each

peak of XRD pattern was calculated and then taking average of them.

The values of lattice parameter “a” determined from the XRD data with an

accuracy of ±0.002 A for all the samples are listed in Table 1 as a function of Zn

content x. Table 1 indicates that the lattice constant increases with the substitution

of Zn2+ ions. The variation of lattice parameter “a” with Zn concentration “x” is

shown in Fig. 2. It is clear from Fig. 2 that lattice parameter “a” increases slowly

with the addition of Zn2+ ions. This behavior can be explained on the basis of

Table 1. Lattice constant (a), X-ray density (dx), measured density (dm), porosity(P ), particle size (t) and specific surface area (S) of Co1−xZnxFe2O4.

Comp. x a (A) dx (gm/cm3) dm (gm/cm3) P (%) t (nm) S (m2/gm)

0.0 8.378 5.302 4.121 22.29 27 53.9370.1 8.380 5.305 4.171 21.49 35 41.1000.2 8.384 5.307 4.213 20.81 38 37.4780.3 8.392 5.309 4.245 20.19 46 30.7270.4 8.400 5.311 4.294 19.56 47 29.7300.5 8.407 5.313 4.321 19.26 51 27.2270.6 8.417 5.314 4.341 18.31 50 27.6430.7 8.431 5.316 4.374 17.52 47 29.186

8.37

8.38

8.39

8.40

8.41

8.42

8.43

8.44

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Lat

tice

con

stan

t 'a'

(Å)

Composition 'x'

Fig. 2. Variation of lattice constant “a” with Zn content x of the seeries Co1−xZnxFe2O4.



0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.75.300

5.302

5.304

5.306

5.308

5.310

5.312

5.314

5.316

5.318

X-r

ay d

ensi

ty d

x (

A0)

Composition 'x'

Fig. 3. Variation of X-ray density dx with Zn content x of the seeries Co1−xZnxFe2O4.

difference in ionic radii. Similar behavior was also observed in other Zn-substituted

ferrite.20,21 The increase in lattice constant is due to replacement of smaller Co2+

ions (0.82 A) by larger Zn2+ ions (0.83 A). Usually, in a solid solution of soft ferrite

within the miscibility range, a linear change in the lattice constant with concentra-

tion of the composition is observed.18

The values of X-ray density (dx), measured density (dm), porosity (P ), particle

size (t), and specific surface area (S) as a function of zinc concentration “x” are

given in Table 1. The dependence of X-ray density on composition is shown in Fig. 3.

It is observed from Fig. 3 that X-ray density increases with increasing Zn content

“x.” This is because of the fact that the increase in molecular weight overtakes

the increase in volume of the unit cell. The porosity is an important parameter

in deciding magnetic susceptibility of the samples. The variation of porosity with

Zn concentration is tabulated in Table 1. It is observed that porosity decreases as

the concentration of zinc increases. It is again due to larger ionic radius of Zn as

compared with Co. The specific surface area values are calculated from Eq. (10)

and are given in Table 1. Table 1 shows that specific surface area values ranges

from 53 to 29 m2/gm.

Using Eq. (1), the particle size of all the samples has been calculated and is

listed in Table 1. Table 1 indicates that wet-chemical co-precipitation method yields

particles of nanosize. The particle size estimated shows random nature with increase

in Zn content though all the samples were prepared under identical conditions. This

may be explained on the basis of hypothesis that the reaction condition, which

favored the formation of new nuclei, may vary randomly with Zn content.22

The distance between magnetic ions. i.e., hopping length in octahedral site, is

(1/4)a2, whereas for the tetrahedral site it is given by (1/4)a3.23 The variation of



2.95

2.955

2.96

2.965

2.97

2.975

2.98

2.985

3.625

3.63

3.635

3.64

3.645

3.65

3.655

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Composition 'x'

LA

LBL

A(Ǻ

)L

B(Ǻ

)

Fig. 4. Variation of hopping lengths in octahedral (LA) with tetrahedral (LB) sites with the Zncontent x of the seeries Co1−xZnxFe2O4.

hopping lengths with Zn content “x” is shown in Fig. 4. It is evident from Fig. 4 that

hopping lengths LA and LB both increase as Zn content increases. This behavior of

hopping length with Zn content “x” is attributed to the variation of lattice constant

with the Zn content “x”.

Using the experimental values of lattice parameter “a” and oxygen positional

parameter “u” and substituting it into Eqs. (2)–(6), tetrahedral and octahedral

bond length (dAX and dBX), tetrahedral edge, shared and unshared octahedral

edge (dAXE, dBXE and dBXEU) were calculated and the values are given in Table 2

and also presented graphically in Figs. 5(a) and 5(b). Figure 5(a) indicates that

the tetrahedral bond length dAX increases as Zn content x increases and octahedral

Table 2. Tetrahedral dAX, octahedral dBX bond lengths, tetrahedraledge dAXE, shared dBXE and unshared dBXEU octahedral edge ofCo1−xZnxFe2O4.

Tetraedge Octa edge

Comp. x dAX (A) dBX (A) dAXE (A) dBXE (A) dBXEU (A)

0.0 2.048 1.913 3.104 2.837 2.970.1 2.049 1.91 3.105 2.833 2.9710.2 2.05 1.907 3.106 2.829 2.9720.3 2.051 1.906 3.109 2.827 2.9750.4 2.053 1.904 3.112 2.824 2.9770.5 2.055 1.903 3.115 2.821 2.980.6 2.057 1.902 3.118 2.82 2.9840.7 2.061 1.901 3.123 2.819 2.988



0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.71.90

1.91

2.04

2.05

2.06

2.07

The

site

bond

leng

ht d

(Å)

Composition 'x'

dAx

dBx

(a)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.72.80

2.85

2.90

2.95

3.00

3.05

3.10

3.15

The

site

edg

e d

(Å)

Composition 'x'

dAXE

dBXE

dBXEU

(b)

Fig. 5. (a) Tetrahedral dAX and octahedral dBX bond lengths with Zn content x of the seriesCo1−xZnxFe2O4. (b) Tetrahedral edge dAXE, shared dBXE, and unshared dBXEU octahedral edgewith Zn content x of the series Co1−xZnxFe2O4.

bond length dBX decreases. Figure 5(b) shows that the tetrahedral edge dAXE in-

creases, unshared octahedral edge dBXEU does not vary much with composition

while shared octahedral edge dBXE decreases. This could be related to the larger

radius of Zn ions as compared with Co ions and the fact that nonmagnetic Zn

occupies strongly tetrahedral A-site.24,25



The cation distribution in soft ferrite is important in understanding their prop-

erties. There are various methods to obtain the cation distribution in soft ferrites,

like XRD, Mossbauer spectroscopy, and neutron diffraction.26 In the present work,

the cation distribution in Co1−xZnxFe2O4 has been obtained from the XRD method

in which X-ray intensity calculations were made and compared with the observed

ones. The X-ray intensity for different planes (Ihkl) is calculated from the following

formula23:

Ihkl = |Fhkl|2P LP . (12)

where Ihkl is relative integrated intensity, Fhkl is structure factor, P is multiplicity

factor, LP is Lorentz polarization factor [(1 + cos2 2θ)/ sin2 θ · cos θ].

The formulae for the structure factor for the planes hkl given by Furahanshi

have been used. The formulae for the multiplicity factor and Lorentz polarization

factor are taken from the literature.18 In calculating the X-ray intensity ratios, the

absorption and temperature factors are not considered in our calculations because

they do not affect the relative intensity calculations for soft ferrites at room tem-

peratures. The planes (220), (400), (422), and (440) have been used to calculate

X-ray intensity ratio. It has been reported that Zn2+ ions have strong site prefer-

ence toward octahedral [B] site. Comparing the site preference energies and from

earlier studies, the cation distribution of pure cobalt ferrite has been accepted as

(Fe1)A [Co1Fe1]

B.27

Using Eq. (11) X-ray intensity ratios for the planes (220), (400), (422), and

(440) have been calculated. The calculations were made for various possible combi-

nations of cations taking into account their site preference energy. The calculated

intensity ratios were compared with the observed intensity ratios. The combina-

tions of cations for which the observed and calculated intensity ratios are in close

agreement are selected and are presented in Table 3. The ratio of Fe3+ ions at

tetrahedral (A) and octahedral [B] site is given in Table 3, which shows that Fe3+

ions concentration at B-site is more than at A-site. Effect of this on magnetic and

electrical properties will be communicated soon.

Table 3. Cation distribution and Fe3+ ratios of the systemCo1−xZnxFe2O4.

Cation distribution Fe3+ tetra

Composition x A-site B-site Fe3+ octa

0.0 (Co0.2Fe1.0) (Co0.8Fe1.0) 1.00000.1 (Zn0.1Co0.1Fe0.8) (Co0.8Fe1.2) 0.6670.2 (Zn0.2Co0.15Fe0.65) (Co0.65Fe1.35) 0.4810.3 (Zn0.3Co0.15Fe0.55) (Co0.55Fe1.45) 0.3790.4 (Zn0.4Co0.15Fe0.45) (Co0.45Fe1.55) 0.2900.5 (Zn0.5Co0.15Fe0.35) (Co0.35Fe1.65) 0.2120.6 (Zn0.6Co0.15Fe0.25) (Co0.25Fe1.75) 0.1430.7 (Zn0.7Co0.15Fe0.15) (Co0.15Fe1.85) 0.081



4. Conclusion

The samples of Co–Zn spinel ferrite are successfully prepared by wet-chemical co-

precipitation technique. The analysis of XRD patterns revealed the formation of

single-phase cubic spinel structure. The lattice constant increases with substitution

of Zn dopant. The particle size obtained from the Scherrer equation shows that it

is of the order of few ten nanometers. Cation distribution data indicated that Zn2+

ion occupies tetrahedral (A) site whereas Co2+ and Fe3+ occupy both (A) and [B]

sites.

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STRUCTURAL PROPERTIES AND CATION DISTRIBUTION OF Co–Zn NANOFERRITES

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