1. Journal of Materials Processing Technology 181 (2007) 106–109
Synthesis and characterization of barium hexaferrite nanoparticles
M. Radwan∗, M.M. Rashad, M.M. Hessien
Electronic Materials Laboratory, Advanced Materials Department,
Central Metallurgical Research and Development Institute (CMRDI) P.O. Box 87 Helwan, Cairo 11421, Egypt
Abstract
This investigation dealt with the synthesis of nanocrystalline barium hexaferrite (BaFe12O19) powders through the co-precipitation–calcination
route. The ferrite precursors were obtained from aqueous mixtures of barium and ferric chlorides by co-precipitation of barium and iron ions using
5 M sodium hydroxide solution at pH 10 in room temperature. These precursors were calcined at temperatures of 800–1200 ◦
C for constant 2 h
in a static air atmosphere. The effect of Fe3+
/Ba2+
mole ratio and addition of surface active agents during co-precipitation step on the structural
and magnetic properties of produced ferrite powders were studied. It is found that the formation of single phase BaFe12O19 powders was achieved
by decreasing the Fe3+
/Ba2+
molar ratio from the stoichiometric value 12–8 and increasing the calcination temperature ≥1000 ◦
C. In addition,
the Fe3+
/Ba2+
mole ratio of 8 the surface active agents promoted the formation of homogeneous nanopowders (ca. 113 nm) of BaFe12O19 at a
low-temperature of 800 ◦
C with resultant good magnetic saturations (50.02 emu/g) and wide intrinsic coercivities (642.4–4580 Oe).
© 2006 Elsevier B.V. All rights reserved.
Keywords: M-type ferrite; Co-precipitation; Magnetic properties; Surfactants; Ultrafine powder
1. Introduction
Barium hexaferrite, BaFe12O19, is a well-known permanent
magnet with great technical importance attracted an exten-
sive attention for the last few decades. BaFe12O19 has a
magnetoplumbite-type structure (hexagonal) with fairly large
crystal anisotropy along c-axis. It has high intrinsic coerciv-
ity (6700 Oe), large saturation magnetization (72 emu/g) and
high Curie temperature (450 ◦C) [1,2]. It was widely used in
the fabrication of commercial permanent magnets, computer
data storage, high-density perpendicular magnetic and magneto-
optic recording, magnetic fluids and certain microwave devices
[1,2]. For ideal performance, ultrafine barium hexaferrite pow-
der (∼ 0.1 ␮m) with homogeneous particle size distribution and
controlled magnetic properties is important [3].
It is difficult to obtain ultrafine and monodispersed parti-
cles by the commercial ceramic method (solid-state reaction)
which involves the firing of stoichiometric mixture of bar-
ium carbonate and ␣-iron oxide at high temperatures (about
1200 ◦C) [4]. In this respect, several low-temperatures chem-
ical methods were investigated for the formation of ultrafine
∗ Correspondence to: Joining and Welding Research Institute, Osaka Univer-
sity, 11-1 Mihogaoka Ibaraki, Osaka 567-0047, Japan. Tel.: +81 6 6879 8693;
fax: +81 6 6879 8693.
E-mail address: radwan72001@yahoo.com (M. Radwan).
BaFe12O19 particles. These methods comprised co-precipitation
[5–8], hydrothermal [9–11], sol–gel [12–14], microemulsion
[2], citrate precursor [15], glass crystallization [16], sono-
chemical [17] and mechano-chemical activation [18]. The chem-
ical co-precipitation method is a low-cost technique suitable for
the mass production compared to the other mentioned methods.
The main drawback is that the particle size is not small and
monodispersed enough for applications like recording media
applications. This paper studies the effect of Fe3+/Ba2+ mole
ratio and the addition of surfactants on the synthesis of nanocrys-
talline barium hexaferrite powder by chemical co-precipitation
method. Such a study is important to understand how to control
the synthesis of single phase barium hexaferrite powder with
homogeneous ultrafine size at low calcination temperature.
2. Experimental
Guaranteed chemically grade ferric chloride (FeCl3·6H2O), barium chloride
(BaCl2·2H2O) and sodium hydroxide (NaOH) were used as starting materials.
Three surfactants; cetyltrimethyl ammonium bromide (CTAB), sodium dodecyl
sulfate (SDS) and Triton X-100 were used. A series of ferric and barium
chlorides solutions in distilled water with various Fe3+/Ba2+ molar ratios (12,
10.9, 9.23 and 8) were prepared. The ferrite precursors were precipitated from
these mixtures by adding gradually sodium hydroxide (5 M) solution at room
temperature to pH 10. The aqueous suspensions were stirred at constant 500 rpm
for 15 min to achieve good homogeneity and attain a stable pH condition. The
(brownish) co-precipitates were filtered off, washed with water and dried in
an oven at 100 ◦C overnight. In order to form the hexaferrite phase, the dry
0924-0136/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmatprotec.2006.03.015

2. M. Radwan et al. / Journal of Materials Processing Technology 181 (2007) 106–109 107
Table 1
XRD results of products obtained from precursors with different Fe3+/Ba2+ mole ratio and calcined for 2 h at 800–1200 ◦C (no surfactants used)
Fe3+/Ba2+ Phases obtained as deduced by XRD
800 ◦C 1000 ◦C 1200 ◦C
12 BaFe0.24Fe0.76O2.88 > BaFe12O19 > Fe2O3 (122.1)a BaFe12O19 > Fe2O3 BaFe0.24Fe0.76O2.88 (140) BaFe12O19 Fe2O3 (191.2)
10.9 BaFe12O19 > Fe2O3 > BaFe0.24Fe0.76O2.88 (143.8) BaFe12O19 Fe2O3 BaO2 (185) BaFe12O19 (191.1)
9.23 Fe2O3 > BaFe12O19 > Ba2Fe6O11 > BaFe0.24Fe0.76O2.88
(98.8)
BaFe12O19 > Fe2O3 BaO2 Ba2Fe6O11 (174.7) BaFe12O19 Ba2Fe6O11 (221.4)
8 BaFe12O19 Fe2O3 (153.1) BaFe12O19 (151) BaFe12O19 (200.6)
a Crystallite size (nm) of BaFe12O19 phase as calculated from XRD results using classic Scherrer formula.
precursors (reddish solids) were heated (calcined) at a rate of 10 ◦C/min in static
air atmosphere up to different temperatures (800, 1000 and 1200 ◦C) where they
were maintained for 2 h. The effect of surface active agents on the formation of
BaFe12O19 was studied by addition of 1000 ppm of the surfactant (CTAB, SDS
or Triton X-100) to the mixed Fe/Ba solution before the precipitation step.
The calcined powders were ground gently by agate mortar prior to their
characterization. The crystalline phases present in the different calcined samples
were identified by X-ray diffraction (XRD) on a Bruker axis D8 diffractometer
using Cu K␣ radiation. The average crystallite size of the powders was estimated
automatically from corresponding XRD data (using X-ray line-broadening tech-
nique employing the classical Scherrer formula). The particles morphologies
were observed by scanning electron microscopy (SEM, JSM-5400). The mag-
netic properties of different calcined powders were measured at room temper-
ature on a vibrating sample magnetometer (VSM, model LDJ 9600-1, USA)
in a maximum applied field of 15 kOe. From the obtained hysteresis loops, the
saturation magnetization (Ms) and coercivity (Hc) were determined.
3. Results and discussion
The effect of Fe3+/Ba2+ mole ratio and calcination temper-
ature on the phase composition of products has been followed
by the XRD analyses. The results obtained are listed in Table 1.
It can be observed that the stoichiometric ratio was not appro-
priate to result in a single phase barium hexaferrite powder and
decreasing the Fe3+/Ba2+ mole ratio (i.e. increasing the Ba con-
centration) promotes the formation of barium hexaferrite phase
at the various thermal treatments. At low calcination temperature
of 800 ◦C, the hematite Fe2O3 phase impurity was found in all
samples. The intermediate BaFe0.24Fe0.76O2.88 phase appears
as a major phase at the stoichiometric sample and its concen-
tration decreases as the Fe3+/Ba2+ mole ratio decreases to 9.23
and disappears at 8. The phases obtained from precursors with
Fe3+/Ba2+ mole ratio of 9.23 were rather complicated in con-
trast to other starting ratios, the hematite became the major phase
and another stable ferrite phase (Ba2Fe6O11) was remained in
the calcined powders even after heating at 1000 and 1200 ◦C.
Increasing the calcination temperature to 1000 ◦C enhanced
the formation of barium hexaferrite phase and a single phase
BaFe12O19 powder was formed at the Fe3+/Ba2+ mole ratio of
8. The intermediate hematite phase was obtained in other start-
ing ratios. But the BaFe0.24Fe0.76O2.88 phase disappeared by
decreasing the Fe3+/Ba2+ mole ratio below the stoichiometric
value. An intermediate barium oxide (BaO2) phase was detected
in the powders with the starting ratios of 10.9 and 9.23.
At the high calcination temperature (1200 ◦C), Fe2O3 was
obtained only in the stoichiometric mixture and single phase
barium hexaferrite powders were obtained from precursors with
starting mole ratios of 10.9 and 8.
The crystallite size of formed single phase barium hexaferrite
powdersascalculatedfromXRDanalysesusingDebye-Scherrer
formula was in the range of 151–200 nm.
The SEM micrograph of single phase barium hexaferrite
powder obtained from starting mixture with the ratio of 8 and
heating at 1000 ◦C is shown in Fig. 1. The powder consists
of micro-aggregates with ultrafine particles mostly of platelet
shape, more longitudinal, with mean diameters (≤200 nm).
The effect of surfactants on the formation and properties
of barium hexaferrite powders was studied by the addition of
a 1000 ppm surfactant to the cations mixture (with Fe3+/Ba2+
mole ratio of 8) prior to the co-precipitation step. Three dif-
ferent surfactants were experimented; CTAB, SDS and Triton
X-100. The dry precursors were then calcined at 800, 1000 and
1200 ◦C for 2 h. The XRD analyses of various calcined samples
revealed the formation of only single phase barium hexaferrite
powders. Fig. 2 gives the XRD pattern of Bafe12O19 obtained
after calcination at 800 ◦C when CTAB was used as the sur-
factant. The pattern shows well-defined Bragg peaks which is
significant of a good crystalline state of the sample. Fig. 3 shows
the effect of various surfactants and calcination temperatures
on the crystallite size of obtained powders. It can be observed
that the addition of surfactants before the co-precipitation step
could prevent agglomeration of particles and grain growth dur-
ing calcination course, which leads to the decrease of grain size
and formation of nanocrystalline single phase barium hexaferrite
powders.
The SEM micrographs of different powders obtained by each
surfactant are given in Fig. 4(a–d). It can be observed that the
Fig. 1. SEM micrograph of obtained single phase BaFe12O19 powder
(Fe3+/Ba2+ = 8, calcination temperature = 1000 ◦C).

3. 108 M. Radwan et al. / Journal of Materials Processing Technology 181 (2007) 106–109
Fig. 2. XRD pattern of BaFe12O19 obtained from a precursor with Fe3+/Ba2+
mole ratio of 8 and calcined for 2 h at 800 ◦C (with CTAB surfactant).
surfactants can control the microstructure of formed barium hex-
aferrite powders. When the anionic surfactant SDS was used,
the 800 ◦C calcined hexaferrite powders (Fig. 4a) had well-
arranged grains with homogeneous nanometer size (∼100 nm).
We think that some kind of repulsion between negative surfac-
tant anions and molecules of Ba and Fe chlorides or hydroxides
existed which prevented the agglomeration of particles dur-
ing the heating step. The nucleation of hexaferrite particles
was homogeneous and the grain growth was hindered which
resulted in good size homogeneity. The cationic CTAB surfac-
Fig. 3. Effect of surfactants and calcination temperature on crystallite size (nm)
of formed BaFe12O19 obtained from precursors with Fe3+/Ba2+ = 8.
tant was found to make the barium hexaferrite particles arranged
in laminates-structure like or clusters which include very small
particles of nanometer size (Fig. 4b). We think that an attraction
forces existed between CTAB cationic surfactant and molecules
of barium and ferric chlorides. When NaOH was added, the bar-
ium and ferric hydroxides molecules were co-precipitated and
arranged in some way in laminates like structure. Increasing the
calcination temperature (to 1200 ◦C) led to the coarsening of
these laminates to few tenths of microns (Fig. 4c). Since Triton
X-100 is non-ionic surfactant, such electrostatic forces are not
exist and less localization of surfactant on interfacial surfaces of
Fig. 4. Effect of surfactants additions on microstructure of synthesized BaFe12O19 powders obtained from precursors with Fe3+/Ba2+ mole ratio = 8: (a) using SDS
and calcined at 800 ◦C, (b) using CTAB and calcined at 800 ◦C, (c) using CTAB and calcined at 1200 ◦C and (d) using X-100 and calcined at 800 ◦C.

4. M. Radwan et al. / Journal of Materials Processing Technology 181 (2007) 106–109 109
Table 2
Magnetic properties of single phase BaFe12O19 powders (Hc and Bs were mea-
sured at room temperature under Hmax = 15 kOe)
Preparation conditions Magnetic properties
Fe3+/Ba2+ Surfactant Calcination
temperature (◦C)
Hc (Oe) Ms (emu/g)
10.9 – 1200 2556 44.9
8 – 1000 3923 28.8
8 – 1200 1670 44.12
8 CTAB 800 4347 45.13
8 CTAB 1000 4358 46.65
8 CTAB 1200 669.9 49.85
8 SDS 800 4518 46.66
8 SDS 1000 4327 45.29
8 SDS 1200 976.6 50.02
8 X-100 800 2050 47.22
8 X-100 1000 4580 46.84
8 X-100 1200 642.4 49.81
barium and ferric molecules was found. On the calcination, the
nucleation and growth of hexaferrite particles were inhomoge-
neous which led to a microstructure with various morphologies
of irregular shapes (Fig. 4d).
The magnetization curves of different powders of single
phase barium hexaferrite were measured at room temperature
under an applied field of 15 kOe. The results of magnetic prop-
erties Hc and Ms are summarized in Table 2. In general, as
commonly observed in the case of ultrafine particles, the sat-
uration magnetization values are lower than the theoretical sat-
uration magnetization for single crystals of barium hexaferrite
(Bs = 72 emu/g) as reported by Shirk and Buessem. Also, the val-
ues of intrinsic coercivity Hc obtained for our samples are lower
than theoretical calculations (Hc ≈ 6700 Oe) using the Stoner
and Wohlfarth model of single-domain particles [2]. Various
theories, including surface area, spin canting and sample inho-
mogeneity have been proposed to account for the relatively low
magnetization in fine particles [15]. It may also be due the pres-
ence of superparamagnetic fractions of very fine particles in the
formed ferrite nanopowders.
4. Conclusions
The observations from the XRD, SEM and VSM studies are
summarized as follows:
(i) A barium surplus is important to synthesize single phase
BaFe12O19 powder by chemical co-precipitation method.
Pure ultrafine barium hexaferrite powders (150–200 nm)
were obtained from precursors with Fe3+/Ba2+ mole ratio
of 8 after calcination at temperatures ≥1000 ◦C for 2 h in
static air atmosphere.
(ii) The addition of surfactants to the starting solution of barium
and ferric cations (Fe3+/Ba2+ = 8) before co-precipitation
step was found to enhance the formation of single phase
barium hexaferrite powders at low calcination temperature
of 800 ◦C.
(iii) The surfactant addition controls the microstructure of
formed barium hexaferrite powders. The anionic SDS sur-
factant led to the formation of well-arranged barium hex-
aferrite grains with homogeneous nanometer sizes. The
cationic CTAB surfactant resulted in micrometer sized lam-
inates or clusters like containing ultrafine individual barium
hexaferrite particles. The non-ionic Triton X-100 surfac-
tant produced nano-size hexaferrite particles with irregular
shapes.
(iv) The formed nano-sized barium hexaferrite powders had
good magnetic saturations (50.02 emu/g) and wide intrinsic
coercivities (642.4–4580 Oe).
References
[1] http://www.aacg.bham.ac.uk/magnetic materials/.
[2] V. Pillai, P. Kumar, M.S. Multani, D.O. Shah, Colloids Surf. A: Physic-
ochem Eng. Aspects 80 (1993) 69.
[3] S. Castro, M. Gayoso, C. Rodr´ıguez, J. Mira, J. Rivas, S. Paz, J.M.
Gren`eche, J. Magn. Magn. Mater. 140–144 (1995) 2097.
[4] M.V. Cabaˇnas, J.M. Gonz´alez-Calbet, Solid State Ionics 63–65 (1993) 207.
[5] S.E. Jacobo, L. Civale, C. Domingo-Pascual, R. Rodrigues-Clements, M.A.
Blesa, J. Mater. Sci. 32 (1997) 1025.
[6] O. Carp, R. Barjega, E. Segal, M. Brezeanu, Thermochim. Acta 318 (1998)
57.
[7] T. Ogasawara, M.A.S. Oliveira, J. Magn. Magn. Mater. 217 (2000) 147.
[8] J. Matutes-Aquino, S. D´ıaz-Castaˇn´on, M. Mirabal-Garc´ıa, S.A. Palomares-
S´anchez, Scripta Mater. 42 (2000) 295.
[9] M.-L. Wang, Z.W. Shih, C.-H. Lin, J. Cryst. Growth 130 (1993) 153.
[10] X. Liu, J. Wang, L.-M. Gan, S.-C. Ng, J. Magn. Magn. Mater. 195 (1999)
452.
[11] D. Mishra, S. Anand, R.K. Panda, R.P. Das, Mater. Chem. Phys. 86 (2004)
132.
[12] C. S¨urig, K.A. Hempel, Ch. Sauer, J. Magn. Magn. Mater. 157–158 (1996)
268.
[13] W. Zhong, W. Ding, N. Zhang, J. Hong, Q. Yan, Y. Du, J. Magn. Magn.
Mater. 168 (1997) 196.
[14] R.M. Garcia, E.R. Ruiz, E.E. Rams, R.M. Sanchez, J. Magn. Magn. Mater.
223 (2001) 133.
[15] V.K. Sankaranarayanan, D.C. Khan, J. Magn. Magn. Mater. 153 (1996)
337.
[16] M. El-Hilo, H. Pfeiffer, K. O’Grady, W. Sch¨uppel, E. Sinn, P. G¨ornert, M.
R¨osler, D.P.E. Dickson, R.W. Chantrell, J. Magn. Magn. Mater. 129 (1994)
339.
[17] K.V.P.M. Shafi, A. Gedanken, Nanostructured Mater. 12 (1999) 29.
[18] O. Abe, M. Narita, Solid State Ionics 101–103 (1997) 103.