Journal of Minerals & Materials Characterization & Engineering, Vol. 10, No.5, pp.397-407, 2011
jmmce.org Printed in the USA. All rights reserved
397
Influence of Processing Parameters on the Magnetic Properties of Mn-Zn
Ferrites
S. A. El-Badry
ME Lab., Phys. Dept., Faculty of Science, Al-Azhar Univ., Nasr City, Cairo, Egypt.
ABSTRACT
Pure MnO
2
, ZnO and Fe
2
O
3
were used to prepare a Mn-Zn Ferrite sample of the nominal
composition Mn
0.64
Zn
0.29
Fe
2
.
07
O
4
. These oxides were mixed firstly for 1hr, and then were
milled for 20 and for 40 hrs. The as-mixed and the milled powders were examined by XRD
and ME spectroscopy. The investigated samples were further mixed with PVA, granulated,
cold pressed and sintered at different temperatures (1000, 1300 and 1400
º
C) for 2 hrs and
were then reinvestigated again. The magnetic properties of all samples before and after
sintering were characterized using VSM at a field of 15 k Oe.
When the powder oxides were milled for 20 hrs, detectable diffusion reaction was observed
where the centers of all XRD peaks (due to Fe
2
O
3
and MnO
2
) shifted to higher 2θ angles,
suggesting that Zn
2+
cations had diffused through Fe
3+
and/or Mn
4+
lattices. The observed
increase in the width of the XRD peaks can be attributed to the refinement of the powders by
milling. Milling of the powder for 40 hrs resulted in the formation of spinel phase of (Zn,
Fe), but MnO
2
was disappeared probably due to the formation of amorphous structure.
Sintering at 1000, 1300, and 1400
º
C resulted in the formation of different spinel (Mn-Zn)
ferrites.
The ME measurements followed the gradual formation the manganese zinc ferrite until
complete formation which observed in the sample that milled for 40 hrs followed by sintering
at 1300
º
C for two hrs. However, it can be concluded that, the processing conditions of such
sample represent are the best conditions for obtaining a soft manganese zinc ferrite (single
phase).
Key words: Mn-Zn ferrite, Ferrites, Soft magnets, XRD, ME spectroscopy and Magnetic
properties.
1. INTRODUCTION
Soft magnets are presently the basic elements of many electronic, electrotechnics and
mechanical devices. They are used now from the base appliances up to different techniques in
the space shuttle. Mn-Zn ferrites represent a group of the most widely used soft magnets in

398 S. A. El-Badry Vol.10, No.5
many electronic applications, eg. Choke coils, loud speaker, noise filters, recording heads,
broad band impulse transformers, etc [1-3]. These materials exhibit excellent properties such
as high permeability, high saturation magnetization, high resistivity and low power loss [4].
But in all cases the preparation technique is a matter of interest. The usual solid state reaction
(ceramic) method appeared now of low interset since it yields ferrite with comparatively
large grain size. Nowadays, powder milling method has been wildly used to prepare small
particle size spinel ferrites [5-11].
It was found that, the magnetic properties of Mn-Zn ferrite are very sensitive to the
processing parameters such as composition, additives, raw materials, attrition milling, and
sintering conditions. The change in one or more of these parameters affects widely the
magnetic properties of such materials [11-15].
On the other hand,
57
Fe ME spectroscopy has been succesflly applied to investigate the
structure of iron compounds including variety of spinel ferrite systems as well as to get
interesting information about their hyperfine structure, cation distribution and their internal
magnetic properties [16].
Accordingly, this article was devoted to investigate the effect of the milling time as well as
the sintering temperature on the magnetic properties of Mn-Zn ferrite applying XRD, ME
spectroscopy and VSM techniques.
2. EXPERIMENTAL
Pure manganese dioxide, zinc oxide and ferric oxide were used to prepare a Mn-Zn ferrite
sample of the nominal composition Zn
0.29
Mn
0.64
Fe
2.07
O
4
. The mean particle size of the used
oxides was between 63~20 µm. These oxides were mixed together using a double cone mixer
until almost complete mixing was obtained (after 1 hr). The mixed powder was firstly
examined by XRD and ME spectral analysis, and was then divided into two parts. The first
part was further mixed with 6 % PVA, granulated and then cold pressed at 40 Mpa, in a
floating die pressing, several compacts of rectangular shape. Some of these compacts were
sintered at 1000
º
C, some others at 1300
º
C, and the rest of the compacts were sintered at
1400
º
C for two hrs. The second part was subjected to mechanical milling using three
dimensional hardened steel balls vial containing high chromium steel balls of 6 mm-diameter
(spex 8000). The weight ratio between the balls and the charged powder was 10:1. The
milling operation was continued for 40 hrs, but some of the milled powders for 20 and 40 hrs
were mixed with 6 % PVA, granulated, and were cold compacted at 40 Mpa. These compacts
were further sintered at one of the following temperatures: 1000, 1300 or 1400
º
C for two hrs.
Extensive investigation by XRD for different processing condition was performed using
Phillips P.W. 1390 diffractometer using Co-K
α
radiation and Mn single-crystal
monchromater. Density measurements were also measured using Archimedes principle in
toluene liquid.

Vol.10, No.5 Influence of Processing Parameters on the Magnetic Properties 399
A conventional constant acceleration ME spectrometer outfitted with 25 m Ci
57
Co
radioactive source was used to obtain the Mossbauer spectra of the studied samples at room
temperature.
The magnetic properties of the powder samples before and after sintering were characterized
using VSM up to a field of 15 k Oe.
3. RESULTS AND DISCUSSION
3.1. X-Ray Analysis
The XRD technique was firstly employed here to investigate the structure of the selected
samples (as-mixed powder, after milling for 20 hrs, after milling for 40hrs as well as after
sintering all samples at 1000, 1300 and 1400
º
C for 2 hrs).
The obtained XRD pattern of the as-mixed powder oxides is shown in (Fig.1 a). The analysis
of this pattern indicated that the XRD peaks of MnO
2
, ZnO and Fe
2
O
3
are all present where
they are the basic constituting oxides. When these mixed powder oxides were subjected to
milling for 20 hrs, it appeared that the centers of all peaks due to Fe
2
O
3
and MnO
2
shifted to
higher 2θ angles, but the centers of all peaks due to ZnO shifted to lower angles (Fig.1 b).
However, it can be supposed that a detectable diffusive reaction occurred. It was suggested
also that Zn
2+
cations had diffused through the Fe
3+
and/or Mn
4+
lattices. Also, it was noticed
that the line width of the XRD peaks increased when the as mixed powder oxides were milled
and their intensity decreased. This broadening may be due mainly to the refinement of the
crystallite size and the accumulation of the internal strain in the milled powders [17]. With
further milling up to 40 hrs (Fig.1C), the diffusive reaction continued and the centers of
Fe
2
O
3
shifted to higher angles and the broadening of the peaks is also increased and their
intensity show great decrease. This was associated with the formation of (Zn,Fe) spinel
phases of the composition (Zn
0.664
Fe
0.336
) (Fe
1.934
Zn
0.66
)O
4
, and the MnO
2
was completely
disappeared. The formation of (Zn,Fe) spinel is due to the continuation of the diffusive
reaction of Zn
2+
into Fe
3+
. The disappearance of the MnO
2
could be attributed to the
formation of amorphous structure as a result of the accumulation of internal strain.
The as mixed powder oxides as well as those milled for 20 hrs and for 40 hrs were all
compacted and sintered for 2 hrs. They were then subjected to extensive XRD investigation
(as exhibited in the experimental part). The analysis of the obtained XRD patterns of all
these compacts that sintered at 1000
º
C for 2 hrs indicated that:
1- The sintered compacts made from the as mixed powder oxides only (before milling)
showed the formation of a manganese ferrite phase of the composition [(FeO)
1.099
(MnO)
0.011
]
and a (Zn,Fe) spinel phase of the composition [Zn
0.664
Fe
0.336
] and a (Zn,Fe) spinel phase of
the composition [Zn
0.664
Fe
0.336
) (Fe
1.934
Zn
0.066
]O
4
.

400 S. A. El-Badry Vol.10, No.5
2- Compacts made from the milled powder oxides for either 20 or 40 hrs, and sintered at
1000
º
C, a (Zn,Fe) spinel phase in addition to different manganese ferrite compositions were
detected in the XRD patterns of these samples. In case of 20 hrs milling, the formed
manganese ferrite phase was of the composition [(FeO)
0.899
(MnO)
0.101
], indicating that higher
Mn content in the formed ferrite phase was obtained than that made from the as-mixed
powder oxides.
3- Increasing milling time to 40 hrs, the content of the manganese ferrite phase increased and
the detected composition was [(FeO)
0.798
(MnO)
0.202
].
Fig. (1) XRD of:
(a) The as-mixed powder oxides for 1 hr.
(b) The as mixed powder oxides for 1 hr, milled for 20 hrs.
(c) The as mixed powder oxides for 1 hr, milled for 40 hrs.
Some general features in the obtained XRD results of these samples could be observed, that
are:
1- The more milling time is, the more broadening of the XRD peaks.
2- The disappearance of the XRD peaks due to MnO of the milled powder for 40 hrs at room
temperature start to appeared again after sintering at 1000
º
C for only 2 hrs associated with
FeO forming (Mn,Fe) ferrite phase of the composition [(FeO)
0.8
, (MnO)
0.2
].
When the investigated compacts were sintered at 1300 or 1400
º
C, a (Mn-Zn) ferrite phase of
the composition [(Mn
0.64
Fe
2.077
Zn
0.29
)O
4
] was detected for all conditions as shown in (Fig. 2,
a - b). The observed differences were shown only in the crystal size and the density. The
more milling time is the finer crystal size obtained, but the higher sintering temperature is the
more dense material obtained. The sintered material at 1400
º
C has the highest density, but

Vol.10, No.5 Influence of Processing Parameters on the Magnetic Properties 401
with coarser grain size than the other sintered compacts at relatively lower temperatures
(1300
º
C).
The crystal sizes of the studied ferrite sample in different stages of milling time and sintering
temperature, was calculated from the XRD and density measurements. All these results are
presented in Table (1).
Fig. (2) XRD patterns of the milled compacts for 40 hrs and sintered for 2 hrs at:
(a) 1300
º
C , (b) 1400
º
C.
Table (1). Effect of milling time and sintering temperatures on the crystal size and
density measurements of the studied Mn-Zn-ferrites.
Milling time ,
hr
Sintering temp.
ºC
Crystal size
nm
Density
g/c
3
As mixed compacts
RT 202 1.65
1000 215 3.2
1300 225 3.83
1400 231 4.65
20hrs milled compact
RT 96 1.03
1000 101 3.15
1300 160 4.3
1400 164 4.75
40hrs milled compact
RT 45 0.83
1000 90 3.11
1300 106 4.2
1400 120 4.75

402 S. A. El-Badry Vol.10, No.5
From Table (1), it is clear that at RT, with increasing milling time the crystal sizes and
density decreases as a result of decreasing particle sizes of the used powders. While for
mixed compacts, 20 hr milled compacts and 40 hrs compacts with increasing milling time the
crystal size decreases and density increases. The increases in the density as the milling time
and sintering temperature can be attributed to the decrease of starting milled powder and so
increase in the diffusion rate during sintering.
3.2. Mossbauer Spectroscopy
It is interesting to apply Mossbauer Effect (ME) spectroscopic analysis to follow the changes
due to the processing parameters (milling time and sintering temperature). It can be also
applied to study the hyperfine structure of the studied samples as well as to follow Zinc
ferrite formation. However, the obtained RT Mossbauer spectra of the studied samples are
presented in both Fig. (3) and Fig. (4).
-10 -50510
Fe
2
O
3
Transsmation %
Velocity (mm/s)
Fig. (3). ME spectra of: The as mixed power oxides for 1 hr, and ferric oxide (Fe
2
O
3
)
Fig.(3) exhibits the ME spectrum of the as mixed powder oxides - only after mixing just for
one hour by the double-cone mixer together with the obtained ME spectrum due to pure α-
Fe
2
O
3
for comparison. The only observable difference between the two spectra is the
appearance of a slight doublet in the spectrum due to the mixed powder oxides. Except this
small doublet, both spectra in this figure show typical coincident. In addition, the calculated
parameters of the magnetic phase in the spectrum of the as mixed powder oxides and that due
to α-Fe
2
O
3
appeared the same. This can be obviously seen in Table (2). On the other hand,
the calculated parameters of the small doublet that appeared in the spectrum of the as mixed
powder oxides, are also presented in Table (2). It was found that, for that doublet, the
quadruple splitting (QS) energy was 0.318 (± 0.01) mm/s, while the isomer shift (IS) energy
was 0.31 (±0.017) mm/s. Also it showed a line width value of 0.338 (± 0.04) mm/s. This

Vol.10, No.5 Influence of Processing Parameters on the Magnetic Properties 403
indicated that the ferrite formation starts in very little proportions with just mixing for one
hour in the double cone-mixer.
Table (2). RT Mossbauer Effect parameters for the measured Mn-Zn ferrite
(Some representative samples)
Sample
Phase Qs Is Lw Hf A%
As mixed
powder
1
2
0.201
0.318
0.367
0.307
0.5
0.34
514
-
93
7
Milled for 20 hrs
1
2
3
0.041
0.0185
1.79
0.279
0.516
0.526
1.085
1.63
0.658
451
383
-
25.1
63.3
11.6
Milled for 40 hrs
1
2
3
4
0.241
0.799
1.36
0.806
0.371
0.428
0.512
1.01
0.613
1.73
1.1
0.557
514
376
-
-
20.1
46.6
13.9
19.4
Milled for 40 hr
and sintered at
1300
º
C
1
2
0.267
0.681
0.405
0.363
0.471
0.733
508
-
18.8
81.2
Fig. (4). ME spectra of milled oxides, (1) mixed for 1 hr, (2) milling for 20 hrs, (3) milling
for 40 hrs , and (4) after milling for 40 hrs and then calcinations for 1 hr at 1000
º
C and
sintering for 2 hrs at 1300
º
C.
Fig. (4) exhibits five representative ME spectra, where these spectra are due to:-
1- The ME spectrum of the as mixed powder oxides after mixing by the double-cone
mixer for only one hour.
2- The ME spectrum of the mixed powder oxides after milling for 20 hrs.
3- The ME spectrum of the mixed powder oxides after milling for 40 hrs.
-10 -50510
(4)
Transsmation %
Velocity (mm/s)
(3)
(2)
(1)

404 S. A. El-Badry Vol.10, No.5
4- The ME spectrum of the mixed powder oxides after calcinations at 1000
º
C for one hr
and sintering at 1300
º
C for 2 hrs.
From these spectra, it is easily to observe the successive decrease of the sub-spectrum due to
the ferromagnetic α-Fe
2
O
3
together with the gradual increase of the paramagnetic (soft-
magnetic) ferrite material. The computer analysis and fitting of the as mixed powder oxides
milled for 20 hrs indicated that, two magnetic iron phases (two sestets) are present. These
two sextets may be due to both A and B sites. On going from spectrum (1) to spectrum (5)
the ferromagnetic phases decreased gradually until complete disappearance in spectrum (5),
while the central paramagnetic doublet increases also gradually, which means the complete
formation of a soft magnetic (Mn,Zn) spinal ferrite. The Obtained ME parameters for all the
measured samples are also presented in Table (2).
Inspecting the ME spectra 2 and 3, it can be supposed that little relaxation effect appear
which may be due to a super-paramagnetic relaxation. This may be in turn due to the effect of
milling and the transformation of the particles to the nano-structural size, as concluded from
XRD. It can be supposed also that the change of the ferromagnetic to paramagnetic material
may be due to the small grain size as well as the disorder introduced by the milling process
[18, 19]. Also, The spectra 1, 2, and 3 show in addition to the central doublets, a complex
spectra in which two supper-imposed sextets appeared by fitting corresponding to the
tetrahedral A and the octahedral B sites of iron cations.
3.3. Magnetic Properties
Fig. (5) shows the magnetization curves for the as mixed powder oxides as well as those
milled for 20 and for 40 hrs, and all these samples were sintered at 1300
º
C,
Fig. (5) Some representative hysteresis loops of: (1) The as mixed powder oxides, (2)
Milled for 20 hr, and (3) Milled for 40 hrs.

Vol.10, No.5 Influence of Processing Parameters on the Magnetic Properties 405
Table (3) summarizes the effect of milling time and sintering temperature on the magnetic
properties of the investigated materials. From this Table, it could be seen that when the
milling time of the as mixed powder oxides was gradually increased (before sintering), the
coercive force (Hc) decreased gradually from 234.3 to 75.81 Oe. It was observed also that the
reminence magnetization (Br) and the saturation magnetization (Bs) increased by about 5 and
8 orders when the compacts were milled for 20 or 40 hrs respectively (see Fig. 6). As the
sintering temperature was gradually increased from 1000 up to 1400
º
C, a critical drop of the
coercive force was obviously seen, while the reminence and the saturation magnetization
showed sharp increase. It is worth to note that, all the values of the measured parameters
(Hc, Br and Bs) of the sintered compacts at 1300 or 1400
º
C showed approximately similar
magnetic behavior.
The observed changes in the magnetic properties of the studied materials could be attributed
to both the reduction in the grain size and the formation of spinel (Zn-Fe) ferrite. It was
concluded that the measured parameters of the compact sintered at 1400
º
C exhibited superior
magnetic properties than all other sintered compacts which may be due to its highest density
value (due to the highest sintering temperature). But, it was easy to observe that the
compacts sintered at 1300
º
C have almost the same magnetic properties of that sintered at
1400
º
C, but the former have finer grain sizes than the later compact that have coarser grain
size. In addition to this the difference between the density values of both these compacts was
small and they appeared to be close to each other. However, it could be concluded that the
best sample is that milled for 40 hrs and sintered at 1300
º
C for 2 hrs. Such processing
conditions could form the same ferrite phase with finer average grain size and could produce
approximately similar magnetic properties to that sintered at 1400
º
C. In addition much
thermal energy could be consumed when compared with the compact sintered at 1400
º
C.
Table (3) Effect of milling time and sintering temperatures on the magnetic
properties of the studied Mn-Zn-ferrites during different stage of processing.
Milling time ,
hr
Sintering
temp.
º
C
Hc,
Oe
Br,
emu/g
Bs,
emu/g
As mixed compacts
20hr milled compact
40hr milled compact
R.T.
1000
1300
1400
R.T.
1000
1300
1400
R.T.
1000
1300
1400
234.4
70.04
11.33
9.76
108.8
55.84
9.14
8.40
75.81
51.09
6.035
5.033
0.030
0.191
0.203
0.246
0.142
0.275
0.344
0.365
0.186
0.333
0.434
0.479
0.24
6.23
18.6
19.3
1.98
8.188
21.72
22.46
3.531
12.641
23.7
24.61

406 S. A. El-Badry Vol.10, No.5
010 20 30 40
0
20
40
60
80
100
120
140
160
180
200
220
240
Corecivity, HC
Milling Time, hrs
RT
1000C
1300C
1400C
( a )
010 20 30 40
0.0
0.1
0.2
0.3
0.4
0.5
Reminance, Br
Milling Time, hrs
RT
1000C
1300C
1400C
( b )
Fig. (6) Effect of milling time and sintering temperature on the magnetic properties of
the studied Mn-Zn-ferrites during different stages of processing.
4. CONCLUSION
The obtained results demonstrate that the process consisting of both mechanical milling
before sintering and then sintering at high temperature is useful for obtaining Mn-Zn ferrite
of homogenous structure with fine size distribution which exhibit superior magnetic
properties Inspecting the obtained results, it could be concluded that mixing the starting
oxides for only one hour was enough to start the ferrite phase formation, as detected by ME
spectroscopy. When the milling time was increased, this acted to decrease the particle size,
resulting in a nano-particles structure. As the sintering temperature was increased, the
density of the studied sample increased and the particle size became coarser, as well as the
measured magnetic parameters became also better. Also, it could be seen that the magnetic
parameters of the samples milled for 40 hrs and sintered at 1300
º
C and 1400
º
C respectively
appeared to be close to each other. Therefore it could be concluded that the best processing
conditions were the milling for 40 hrs followed by the sintering at 1300
º
C for 2 hrs.
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