Study of the Bulk Magnetic and Electrical Properties of MgFe<sub>2</sub>O<sub>4</sub> Synthesized by Chemical Method

doi:10.4236/msa.2011.211209

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Materials Sciences and Applications, 2011, 2, 1564-1571

doi:10.4236/msa.2011.211209 Published Online November 2011 (http://www.SciRP.org/journal/msa)

Study of the Bulk Magnetic and Electrical

Properties of MgFe2O4 Synthesized by Chemical

Method

Sheikh Manjura Hoque1, M. Abdul Hakim1, Al Mamun1, Shireen Akhter1, Md. Tanv i r H asan2,

Deba Prasad Paul2, Kamanio Chattopadhayay3

1Materials Science Division, Atomic Energy Centre, Dhaka, Bangladesh; 2Department of Physics, Chittagong University, Chittagong,

Bangladesh; 3Department of Materials Engineering, Indian Institute of Science, Bangalore, India.

Email: [email protected]

Received June 30th, 2011; revised August 12th, 2011; accepted August 27th, 2011.

ABSTRACT

Nanocrystalline Magnesium ferrite has been prepared by chemical co-precipitation technique. Structural characteriza-

tion has been performed by X-ray diffraction. Formation of ferrites has also been studied by using FTIR. Frequency

dependence of real and imaginary part of initial permeability has been presented for the samples sintered at different

temperatures. Real part of initial permeability, increases with the increase of grain growth. The loss component repre-

sented by imaginary part of initial permeability decreases with frequency up to the measured frequency of this study of

13 MHz. Curie temperatures have been determined from the temperature dependence of permeability. Curie tempera-

tures for the samples of this composition do not vary significantly with the variation of sintering temperatures. B-H loop

measurements have been carried out by B-H loop tracer. Transport property measurements haven been carried out by

electrometer and impedance analyzer.

Keywords: MgFe2O4, Nanograins, Complex Initial Permeability, B-H Curves, Transport Properties

1. Introduction

Magnesium ferrite (MgFe2O4) is an important magnetic

oxide with spinel structure. Magnesium ferrite and allied

compounds have found wide spread applications in mi-

crowave device because of their low magnetic and di-

electric losses and high resistivity. MgFe2O4 enjoys spe-

cial attention for microwave application such as circula-

tors, insulator and phase shifters [1]. Magnesium ferrite

is also used in high-density recording media, heteroge-

neous catalysis and sensors. MgFe2O4 is also known for

its good photoelectric effect [2-4]. Synthesis of MgFe2O4

nanoparticle has been attempted by several investigators

[5-8]. Rane et al. [9] have studied dielectric behavior of

MgFe2O4 prepared from chemically beneficiated iron ore

rejects and have arrived at the conclusion that chemically

beneficiated iron ore rejects can, hence, be effectively

used in the synthesis of high quality ferrites. Candeia et

al. [10] have studied MgFe2O4 pigment obtained at low

temperature by polymeric precursor method. Doroftei et

al. [11] have studied microstructure and humidity sensi-

tive properties of MgFe2O4 ferrite with Sn and Mo sub-

stitutions prepared by self-combustion method. Gateshki

et al. [12] have studied structure of nanocrystalline

MgFe2O4 from X-ray diffraction, Rietveld and atomic

pair distribution function analysis. Though numbers of

research papers are available in the literature on MgFe2O4,

synthesis of nanoferrites by chemical method is still con-

sidered to be in the infancy state in terms of reproducibil-

ity and further improvement.

MgFe2O4 is known for its ideal mixed-spinel structure

consists of a face-centered cubic close-packed oxygen

sublattice in which a fraction of the tetrahedral (T) and

octahedral (O) sites are filled by Mg ions. The crystal

structure of spinel ferrites can be formulated in greater

detail as (Mg1–Fe)[MgFe2–]O4. The parentheses and

the square brackets denote cation sites of fourfold (T)

and sixfold [O] oxygen coordination, respectively where,

 represents the so-called degree of inversion (defined

either as the fraction of the (T) sites occupied by Fe3+

cations or as the fraction of the [O] sites occupied by

Mg2+ cations. It is widely known that since Mg+2 is non-

magnetic, magnetic moment of MgFe2O4 is derived from

Study of the Bulk Magnetic and Electrical Properties of MgFeO Synthesized by Chemical Method1565

2 4

the particular type of cation distribution. The cation dis-

tribution in spinel ferrites upon which many physical and

chemical properties depend, is a complex function of

processing parameters. It is an established fact that there

is a remarkable effect of initial particle size on bulk pro-

perties of sintered product. Further chemically synthe-

sized particles contain lesser amount of impurity and

higher surface to volume ratio. Conventionally, sintering

temperature of MgFe2O4 is very high. There is a possibil-

ity of reducing the sintering temperature of technologi-

cally important MgFe2O4 to attain optimum properties

and thus reduce processing cost. The purpose of the pre-

sent study is to investigate the effect of nanosized parti

cle as starting material on bulk properties of MgFe2O4

sintered at various temperatures.

2. Experimental

We have used a standard co-precipitation technique to

produce fine particles of MgFe2O4. The analytical grade

of Fe(NO3)3·9H2O, Mg(NO3)2·6H2O and NaOH were

mixed in required molar ratio and added to 8 M NaOH

solution with constant stirring at room temperature. The

precipitate was heated to 80˚C with constant stirring.

When reaction was completed the precipitate was centri-

fuged at 15,000 rpm for 20 minutes, then washed and

filtered for 10 times with distilled water. Finally, the pre-

cipitate was heated at 90˚C for 36 hours. The powder was

pelletized and sintered at various temperatures in the

range of 200˚C - 1400˚C. Formation of ferrites has been

studied by X-ray diffraction and also by FTIR. Micro-

structure has been studied using scanning electron mi-

croscope. Complex initial permeability and dielectric con-

stants have been measured by using impedance analyzer.

B-H loops were studied using B-H loop tracer. Tem-

perature dependence of resistivity has been studied by

electrometer and laboratory built furnace.

3. Results and Discussion

In Figure 1, X-ray diffraction patterns of samples cal-

cined in the range of 500˚C to 1000˚C for 3 hours have

been presented. The curves reveal decrease of FWHM

with the increase of sintering temperature. The grain size

has been obtained from Scherrer’s formula using Full

Width Half Maxima (FWHM) and peak position of the

sample after correcting instrumental broadening and pre-

sented in Figure 2. The grain size was estimated to be

around 21 nm for the sample sintered at 500˚C. With the

increase of sintering temperature the grain size increases

dramatically and reached the value of around 75 nm for

the sample sintered at 1000˚C. For the further increase of

sintering temperature of around 1200˚C - 1400˚C, it was

not possible to measure grain size with X-ray diffraction

since instrumental broadening at this point was compara-

Figure 1. X-ray diffraction patterns of MgFe2O4 for the

samples sinte red at different t emperature s for 3 hr.

Figure 2. Variati on of grain size w ith sintering temperature

for 3 hr of sinte r ing time.

ble to the value of FWHM.

The variation of lattice parameter with sintering tem-

perature has been presented in Figure 3. The variation in

lattice parameter for the sample prepared from nanograins

has been studied by several investigators [13,14]. Han-

kare et al. has reported the value of lattice parameter as

8.33 Å [13] while Sattar et al. has found lattice pa-

rameter higher than the standard JCPDS data [14]. The

lattice parameter increases sharply during sintering upto

700˚C. No change in lattice parameter can be detected

beyond this temperature indicating completion of ferriti-

zation. This corresponds to sintered grain size of 26 nm.

In Figure 4, X-ray diffraction pattern of MgFe2O4 sin-

Study of the Bulk Magnetic and Electrical Properties of MgFeO Synthesized by Chemical Method

1566 2 4

Figure 3. Variati on of lattice para meter w ith sintering tem-

pera ture for 3 hr s intering time .

Figure 4. X-ray diffraction pattern of MgFe2O4 for the

sintering temperature of 1000˚C for 3 hr.

tered at 1000˚C has been presented. All the peaks were

indexed in terms of the known structure of MgFe2O4.

Lattice parameter reached a reported value of 8.367 Å at

1000˚C, which is close to the reported equilibrium value

for MgFe2O4 i.e. 8.376 Å.

The FTIR spectra of MgFe2O4 nanoparticle sample in

the range 1000 - 350 cm–1 is shown for the samples

sintered in the range of 1200˚C - 1400˚C in Figure 5. In

the FTIR spectrum of MgFe2O4 in the range 1000 - 350

cm–1 absorption bands correspond to the vibration of tet-

rahedral and octahedral complexes at ν1 ~ 572 cm–1 and

ν2 ~ 409 cm–1 at 1200˚C respectively, which is indicative

of the formation of spinel ferrite structure. The presence

Figure 5. FTIR spectra of MgFe2O4 sintered at dferent

resence of different ionic states in that site. It is seen

ture of the samples of MgFe2O4 sin-

mportant criteria of soft

temperatures.

from the FTIR data that the normal mode of vibration of

tetrahedral cluster is higher than that of octahedral cluster.

This can be due to the shorter bond length of tetrahedral

cluster than the octahedral cluster. It can be noted that the

value of ν1 and ν2 remain almost unchanged with the sin-

tering temperature. This indicates that there is very little

change of cation distribution with the increase of sinter-

ing temperature in the range of 1200˚C to 1400˚C. It will

be seen later that there is almost no change in Curie tem-

perature with the increase of sintering temperature, which

further indicate that there is very little or no change of

cation distribution.

SEM microstruc

red at 1250˚C, 1350˚C and 1400˚C has been presented

in Figure 6 with the magnification of 3000. Calculated

grain size for MgFe2O4 has been obtained as 4, 5 and 10

µm for the samples sintered at 1250˚C, 1350˚C and

1400˚C respectively. It can be observed from the figure

that the grain size of the sample sintered at 1250˚C is

smaller. With the increase of sintering temperature, micro-

structure becomes more homogeneous in association with

an increase of grain size. Further, considerable amount of

pores can be seen in the microstructure of sample sin-

tered at 1250˚C. Amount of pores decrease with the in-

crease of sintering temperature.

Frequency stability of µ is an i

agnetic materials for its application in microwave de-

vices. The general characteristic of frequency spectrum

of permeability curves is μ remains fairly constant up to

some critical frequency beyond which μ decreases char-

acterized by the onset resonance of loss governed by

Snoek’s law. At critical frequency μ drops rapidly.

of long shoulder for the A and B site is indicative of the

Study of the Bulk Magnetic and Electrical Properties of MgFe2O4 Synthesized by Chemical Method

1567

Figure 6. SEM micrographs for the samples sintered at 1250˚C, 1350˚C and 1400˚C for 3 hr.

The nature of these curves and critical frequency at

equency spectrum of real part of ini-

tia

cause of the increase of grain size and densification. At

hich onset of resonance takes place depend on the ionic

states of cations, density and grain size. The permeability

generally increases with the increase of grain size. The

presence of small grain size interferes with wall motion,

which decreases both real and imaginary part of perme-

ability and increases stability region of μ′. At higher fre-

quencies, losses are found to be lower if domain wall

motion is inhibited and the magnetization is forced to

change by rotation.

Figure 7 shows fr

l permeability μ′ at various sintering temperatures. μ′

increases with the increase of sintering temperature be-

higher sintering temperatures inhibition of domain wall

mobility decreases to a great extent, which leads to the

increase of μ′. In Figure 8, frequency spectrums of

imaginary part of initial permeability μ″ are presented at

different sintering temperature. The low frequency value

of μ″ increases with the increase of sintering temperature

due to lower inhibition of domain wall motion. This also

increases natural frequency of precession, which absorbs

more energy leading to enhancement of losses. Frequen-

cy responses of both real and imaginary part of per-

meability for the samples of this study are characterized

by high degree of stability which is suitable for microwave

Study of the Bulk Magnetic and Electrical Properties of MgFeO Synthesized by Chemical Method

1568 2 4

Fig ure 7 . Fr equency de pend enc e of re al and i magi nary part

of initial permeability (μ and μ) for the samples sitere d at n

1250˚C, 1350˚C and 1400˚C.

Figure 8. Temperature dependence of initial permeability μ

for the samples sintered at 1250˚C, 1350˚C and 1400

Curie temperature measurement involves the meas-

rmeability μ′ varying with temperature. In

˚C.

applications.

urement of pe

gure 9, temperature dependence of permeability of

samples obtained at various sintering temperature of

1250˚C, 1350˚C, 1400˚C for 3 hrs are presented. At Cu-

rie temperature Tc, complete spin disorder takes place.

The sharpness of the fall of μ′ at Tc indicates the homo-

geneity of the studied samples. From Figure 9, it can be

observed that the Curie temperature does not vary with

sintering temperature. This complies with intrinsic nature

of Curie temperature, which does not vary with grain size

and porosity. Invariance of Curie temperature with sin-

tering temperature also implies that there is little or no

Figure 9. Temperature dependence of initial permeaility μ′

for the samples sintered at 1250˚C, 1350˚C and 1400

ure

nge of 1200˚C - 1400˚C in compliance with the results

1400˚C for 3

n Figure 12, coercivity, remanent

es, several general conditions must be fulfilled [15].

˚C.

change of cation distribution in the sintering temperat

obtained from FTIR presented in Figure 5.

In Figure 10, primary induction curves of MgFe2O4 of

the samples sintered at 1250˚C, 1350˚C and

have been presented. The curves are characterized by

the pinning effect of the domain wall movement. This is

due to the presence of increased number of pores and

also because of smaller grain size, which leads to in-

creased volume fraction of grain boundary. Both the

pores and grain boundaries inhibit domain wall move-

ment. With the increase of sintering temperatures, pores

and grain boundary effects are reduced due to higher

densification and grain growth. This is manifested in the

initial part of primary induction curve known as Rayleigh

region where lower field is required to achieve higher

magnetization due to the elimination of more number of

defects in the sample with progressive increase of sin-

tering temperatures.

In Figure 11, B-H hysteresigraphs of the sintered sam-

ples are presented. I

tio and core loss derived from Figure 11 are presen-

ted. From both the figures, it may be observed that the

coercivity and remanent ratio decrease with the increase

of sintering temperature. This is typically valid for ex-

trinsic properties, which depends on grain size and po-

rosity of the samples. Core loss, which is mainly related

to the area of the hysteresis loops decrease with the in-

crease of sintering temperature. More importantly, it might

be noticed the shape of the B-H curves, which possess

higher squareness ratio. Maximum remanent ratio is around

0.8.

In order to attain high remanent ratio in polycrystalline

ferrit

rst of all, they should have a high degree of symmetry

Study of the Bulk Magnetic and Electrical Properties of MgFeO Synthesized by Chemical Method1569

2 4

Figure 10. Primary induction curves of MgFe2O4 for the

samples sintered at 1250˚C, 1350˚C and 1400˚C.

Figure 11 . B-H hysteresis lo ops of M gFe2O4 for the samples

sintered at 1250˚C, 1350˚C and 1400˚C.

cture should have

s many directions of easy magnetization as possible.

(magnetic homogeneity), i.e., their stru

This condition is realized more closely in ferrites with a

cubic lattice structure and a negative K1 constant. Sec-

ondly, crystallographic anisotropy should predominate

over other types of anisotropy (shape, stress). This means

a need for low internal stresses, magnetostriction, and

porosity as well as high homogeneity of the material. In

this case the ratio K1/MS (MS is the saturation magneti-

zation) should be rather high. Thirdly, magnetic coupling

between grains, determined by the ratio MS2/K1, should

be strong. The second and third conditions impose con-

tradictory requirements on the values of K1 and MS. Con-

Figure 12 . Sintering te mperature dependence of Co ercivity,

Rema nent ratio and Core los s .

gular hysteresis loop

nly if they have compositions for which the values of K1,

ave been presented. Room tempera-

sequently, ferrites will have a rectan

MS lie within a certain range. Such ferrospinels should

have the required homogeneity of the residual porosity

and grains. They should also include micro-scopic inho-

mogeneities which are required for forming domains of

reverse magnetization or restraining the motion of the

boundaries of such domains before a field of certain

strength is applied.

In Figure 13, dc resistivity data as a function of in-

verse temperature h

re resistivity for all the samples sintered in the range of

1250˚C - 1400˚C is more than around ~106  cm. The

resistivity decreases with increasing sintering tempera-

tures. The value of ρ is the lowest for the samples sin-

tered at 1400˚C. When polycrystalline ferrites are con-

sidered, the bulk resistivity arises from a combination of

crystallite resistivity and the resistivity of crystallite boun-

daries. The boundary resistivity is much greater than that

of the crystallite resistivity. Thus the boundary has the

greatest influence on the dc resistivity. The decrease of

resistivity is also related to the decrease of porosity at

higher sintering temperature since pores are non-con-

ductive, which increases resistivity of the material. The

resistivity increases with the increase of porosity at lower

sintering temperature because charge carriers on their

way face the pores. The activation energy decreases with

increasing sintering temperature. Decrease of activation

energy with the increase of sintering temperatures may

be attributed to the fact that at a high sintering tem-

perature, partial reduction of Fe3+ to Fe2+ takes place

locally and these places act as donor centre. The con-

duction mechanism is due to hopping of electrons of the

type Fe2+Fe3+.

Study of the Bulk Magnetic and Electrical Properties of MgFeO Synthesized by Chemical Method

1570 2 4

mined using LCR circuit. The variation

The dielectric constants of the ferrites in the form of

pellets were deter

real and imaginary part of dielectric constant (



' and



)

as a function of frequency for MgFe2O4 for various sin-

tering temperatures are shown in Figures 14 and 15. From

Figure 14, dispersion in dielectric constants can be ob-

served for all the samples sintered at various tempera-

tures. To explain the dielectric dispersion in ferrites,

grain and grain boundaries were assumed to be two dif-

ferent layers each having the same dielectric constant. As

the frequency rises from a low value the bulk resistivity ρ

and dielectric constant



fall and become asymptotic to

lower values at higher frequencies. This variation has the

characteristic of relaxation and is attributed to the granu-

lar structure of ferrites, in which crystallites are separated

Figure 13. Temperature dependence of resistivity ρ for the

samples sintered at 1250˚C, 1350˚C and 1400˚C.

Figure 15. Frequency dependence of imaginary part diele c-

tric constant



for the samples sintered at 1250˚C 50˚C

and 1400˚C.

s the structure behaves as a compound die-

by chemical

hnique and sintered at different tem-

, 13

by boundaries having much higher resistivity than the cry-

tallites. Thus

lectric. At low frequencies the impedance of the crysta-

llites are negligible compared to that of the boundary.

The dielectric constant approaches to the value, which

is analogous to calculating dielectric properties from mea-

surements on a specimen between the plates of capa-

citor, using a dielectric length 1/n times the actual value.

At very high frequencies the boundary capacitance be-

comes short circuited with the boundary resistance and

the bulk dielectric properties approach those of crystal-

lites. Real part of dielectric constant exhibits rapid in-

crease with decrease of frequency. The imaginary part of

dielectric constant increase much more slowly compared

to usual values of



for ferrites. Figure 15 shows no

extra peak, because of high bulk resistivity.

4. Conclusions

Nanocrystaline MgFe2O4 has been prepared

co-precipitation tec

peratures. The particleize has been obtained from

Scherrer’s formula and found around 26 nm at 700˚C

where single phase MgFe2O4 has formed. When the sam-

ples were calcined at higher temperatures subsequent grain

growth has taken place. Further calcinations at 1000˚C

led to the grain size of 75 nm. SEM micrographs reveal

increase in grain size with increasing sintering tempe-

ratures along with significant decrease of pores. Curie

temperature remains unchanged with the increase of

sintering temperature. The B-H loops are characterized

by higher squareness ratio, the maximum value of which

is around 0.8. The resistivity decreases with the increase

of sintering temperature. The decrease of resistivity is re-

Figure 14. Frequency dependence of real part dectric

constant



for the samples sintered at 1250˚C, 135C and

1400˚C.

iel

0˚

Study of the Bulk Magnetic and Electrical Properties of MgFe2O4 Synthesized by Chemical Method

1571

on, the su-

of Science, Informatio

Government of People’s Re-

Current Trends in Applications of Magnetic

Ceramic Materials Science, Vol

15, No. 5, 19907/BF02745

lated to the increase of grain size and decreasing porosity

since pores are non conductive, which increases the resis-

tivity of the material. The highest values of dielectric

constant (



) can be observed for the samples having lo-

wer resistivity. Dispersion in dielectric constant is ob-

served for all the samples at lower frequency.

5. Acknowledgements

The authors acknowledge with great appreciati

pport provided by Ministry

Communication Technology,

n and

public of Bangladesh, Bangladesh Atomic Energy Com-

mission and International Science Program, Uppsala Uni-

versity, Sweden.

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