Materials Sciences and Applications, 2011, 2, 1564-1571
doi:10.4236/msa.2011.211209 Published Online November 2011 (
Copyright © 2011 SciRes. MSA
Study of the Bulk Magnetic and Electrical
Properties of MgFe2O4 Synthesized by Chemical
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.
Received June 30th, 2011; revised August 12th, 2011; accepted August 27th, 2011.
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)[MgFe2–]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-
Copyright © 2011 SciRes. MSA
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
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
Copyright © 2011 SciRes. MSA
Study of the Bulk Magnetic and Electrical Properties of MgFe2O4 Synthesized by Chemical Method
Copyright © 2011 SciRes. MSA
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-
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
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
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].
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
In order to attain high remanent ratio in polycrystalline
rst of all, they should have a high degree of symmetry
Copyright © 2011 SciRes. MSA
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+.
Copyright © 2011 SciRes. MSA
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
for the samples sintered at 1250˚C, 135C and
Copyright © 2011 SciRes. MSA
Study of the Bulk Magnetic and Electrical Properties of MgFe2O4 Synthesized by Chemical Method
Copyright © 2011 SciRes. MSA
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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