Materials Science s a nd Applications, 2011, 2, 1644-1653
doi:10.4236/msa.2011.211219 Published Online November 2011 (
Copyright © 2011 SciRes. MSA
Dispersibility, Shape and Magnetic Properties of
Nano-Fe3O4 Particles
Xiaojuan Liang1, Haowei Shi2, Xiangchen Jia2, Yuxiang Yang2*, Xiangnong Liu3
1College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, China; 2Department of Chemistry, East China
University of Science & Technology, Nanjing, China; 3Analysis Test Center, Yangzhou University, Yangzhou, China.
Email: *
Received July 25th, 2010; revised November 19th, 2010; accepted September 8th, 2011.
Nano-Fe3O4 particles were prepared by a two-step microemulsion method, the influence of molar ratio of water to
NP-5 (R), alkali concentration and temperature on dispersibility and shape of the nanoparticles were discussed. Mag-
netic studies were also carried out using VSM in this paper. It was found that the optimum preparation parameters are
R = 6.0, alkali concentration = 2.5 mol·L–1, initial total iron concentration as 0.88 mol·L–1, and the temperature being
30˚C, the prepared nano magnetite particles have uniform size and good dispersibility with a crystal structure belong-
ing to cubic Fe3O4 and lattice parameters of a = 8.273 Å. The results of magnetic studies show, magnetic properties of
particles are influenced by dispersibility of nanoparticles which depends on size of clusters. The better dispersibility of
nanoparticles leads to more ordered inner magnetic vector, and so the stronger magnetic behavior of nano-Fe3O4 par-
Keywords: Nano-Fe3O4 Particle, Dispersibility of Nanoparticles, Magnetic Properties, Saturation Magnetization
1. Introduction
Magnetic nanoparticles have been widely studied be-
cause of their fascinating properties and wide range of
potential applications in ferrofluids, information storage,
pigment, medicine, biomedical and bioengineering, etc.
[1-3] The nano magnetite particles can be synthesized by
precipitation from the solution of mixed Fe(II)/Fe(III)
salts in alkaline medium. Besides this, many techniques
have been used to synthesize magnetite such as thermal
decomposition [4] hydrothermal synthesis [5], coprecipi-
tation of an aqueous solution of ferrous and ferric ions by
a base [6-8],oxidation of the ferrous hydroxide gels using
KNO3 [9], γ-ray irradiation [10], microwave plasma syn-
thesis [11] sol-gel [12], nonaqueous route [13-15] etc.
Many applications depend on their size and stoichiome-
try of particles, however the dispersibility and shape of
prepared particles varies with the hydrolysis condition,
the additive surfactant[4] and organic compound [5], most
of them exhibit nano spherical particles [16-18].
Many reports have not systematically studied various
factors affecting dispersibility and shape of nano-Fe3O4
particles, especially the relationship between dispersibil-
ity and their magnetic behavior. So in this paper, we re-
port the preparation process of nano-Fe3O4 particles us-
ing two-step microemulsion method. The different fac-
tors affecting dispersibility of nano-Fe3O4 particles, in-
cluding NaOH concentration, reaction temperature, wa-
ter-surfactant ratio, and initial total iron concentration,
are discussed. The relationship between the magnetic
properties and dispersion behavior of nano-Fe3O4 parti-
cles is also studied.
2. Experimental
2.1. Synthesis of Nanoparticles Fe3O4
Surfactant NP-5, cosurfactant butanol, and kerosene were
mixed in the ratio of 1:1:10, the muddy mixed solution
was then stirred until a clear and transparent solution was
obtained. The previous solution was divided into two
parts of (1) and (2).
Firstly, the boiled deionized water was added to the
solution of (1) with a ratio R (R is the molar ratio of wa-
ter to NP-5), the microemulsion became clearer and clearer
through stirring. Then certain amount of FeCl2·4H2O and
FeCl3·6H2O were added into the microemulsion system
with the molar ratio of Fe2+ to Fe3+ as 3:2 while vigor-
ously stirring. The microemulsion labeled as (1) became
brown-yellow and transparent.
Secondly, the boiled NaOH solution with the concen-
Dispersibility, Shape and Magnetic Properties of Nano-FeO Particles1645
3 4
tration at 2.0 mol/L, 2.5 mol/L, 3.0 mol/L, and 3.5 mol/L
were added to the solution of (2) with the corresponding
ratio R value previously mentioned in above step, the
microemulsion labeled as (2) became clear and trans-
parent while stirring.
After stirring microemulsion (1) and (2) for 3 h, the
microemulsion (2) was dropped into the microemulsion
(1) with N2 gas passing through, the brown-yellow solu-
tion immediately turned black. The mixed system was
stirred for 3.0 h and left standing for 1 h at 80˚C. After
that, the upper layer was transparent and the bottom layer
was black, then the upper layer was discarded and the
bottom layer was washed with absolute alcohol for twice.
The obtained product was dried in a vacuum oven at
80˚C for 2 h, and calcined at 350˚C for 4 h, following the
dry product was calcined in tube type electric-resistance
furnace at 350˚C for 4 h. Eventually, the black powders
were obtained.
2.2. Characterization of Nanoparticles Fe3O4
The x-ray diffraction pattern of the sample was recorded
by D/max 2550 VB/PC x-ray diffractometer, using Ni-
filtered with Cu Kα radiation (40 mA, 40 KV, 1˚(2θ)
min–1) at room temperature. The dispersibility and shape
of samples were observed by Tecnai-12 transmission
electron microscope (TEM) (120 KV).
3. Results and Discussions
Figure 1 shows the XRD patterns for magnetic parti-
cles prepared on the condition of R = 6.0 and CNaOH = 2.5
mol/L, the X-ray diffraction patterns of magnetic parti-
cles all display sharp peak with strong diffraction inten-
sity, and low background, the indices (220) and (400)
labeled by red color are found to be corresponding to 2θ
values of 31.4 and 45.4 respectively, in a good agree-
ment with the JCPDS card 26 - 1136, which belongs to
cubic system. However, the indices (220) and (400) la-
20 40 60 80
220 400
511 622
Intensity (a.u.)
2-Theta (degree)
220 JCPDS:26-1136
Figure 1. X-ray diffraction pattern of the nano magnetite.
beled by blue color and the indices (311), (422), (511),
(440), (620), (622) and (642) are corresponding to the
standard diffraction card JCPDS 19-629(pure Fe3O4). It
is demonstrated that the obtained products are mixture of
two kinds of cubic nano-Fe3O4 particles, with corre-
sponding JCPDS card being 19 - 629 and 26 - 1136 re-
The TEM images shown in Figure 2 reveals the nano-
crystallite nature of magnetite particles with a good dis-
persibility, the average particle size measured from the
TEM images has been found to be 22 nm.
3.1. Effect of Different NaOH Concentration on
Magnetite Morphology
In the preparation, the alkali concentration and water-
core of microemulsion are two chief factors that affect
dispersibility of Fe3O4 particles. In order to discuss the
effects of alkali concentration on the dispersibility and
shape of Fe3O4 particles, we performed five experiments
under alkaline condition at concentration of 1.5, 2.0, 2.5,
3.0 and 3.5 mol·L–1 respectively. The dispersibility of
prepared magnetite was investigated by transmission
electron microscope, five TEM images of magnetite are
shown in Figure 3.
It is found when the concentration of NaOH is lower
than 2.0 mol·L–1 the agglomerated granules appear in the
prepared sample, and the spindle-like particles are
formed. The image recorded in Figure 3(a) exhibits
rod-like form with spindle-like form crossing over. It is
because the precipitate of Fe3+ occurs at pH in the range
of 3 - 4, which is calculated by Kθsp, Fe(OH)3, but precipi-
tate of Fe2+ occurs at pH in the range of 8 - 9 calculated
by Kθsp, Fe(OH)2, indicating the amount of NaOH for pre-
cipitate of Fe3+ is much less than that for precipitate of
Fe2+. So when the shortfall amount of NaOH is intro-
Figure 2. TEM morphology of the nano magnetite.
Copyright © 2011 SciRes. MSA
Dispersibility, Shape and Magnetic Properties of Nano-FeO Particles
1646 3 4
(a) (b) (c)
(d) (e)
Figure 3. The morphology of Fe3O4 parti cl es prepar e d un de r al kal i ne c on di ti o n at co nc e ntr at io n of (a) 1 .5 ; (b) 2 .0 ; (c ) 2. 5 ; (d)
3.0; (e) 3.5 mol/L.
duced into the mix solution containing Fe3+ and Fe2+ ions,
the pH is measured about 7.5, the Fe3+ ions preferentially
form precipitates by itself instead of co-precipitating with
Fe2+ ions, the results are that more orange red FeOOH
phase is formed first, but less Fe3O4 phase is formed.
When the concentration of NaOH reaches 2.0 mol·L–1
with the pH measuring about 8.5, the spherical particles
and local agglomeration of granules are formed, as
shown in Figure 3(b) The reason is that completely co-
precipitation of Fe3+ with Fe2+ ions generally occur at pH
above 9.2 as reported by reference [19]. So at the pH
about 8.5, the Fe3+ ions begin to co-precipitate with the
Fe2+ ions, and form the Fe3O4 phase. But this time, the
residual Fe3+ ions hydrolyzes into tiny FeOOH particles,
due to lower pH value than that of coprecipitation of Fe3+
with Fe2+ ions, as a result, the tiny FeOOH particles pro-
duced by hydrolysis easily form local agglomeration in
the sample.
In contrast to Figure 3(b), the image recorded in Fig-
ure 3(c) exhibit spherical form with well uniform sizes,
its average size is measured about 22 nm. The experi-
mental results demonstrate that the optimum NaOH con-
centration for coprecipitation of Fe3+ with Fe2+ ions is 2.5
mol/L, with the pH measuring above 9.2, the reaction
mechanism can be inferred as the following:
Fe2+ + Fe3+ + OH Fe(OH)2/Fe(OH)3 (coprecipita-
tion of Fe3+ with Fe2+)
Fe(OH)2 + Fe(OH)3 FeOOH+ Fe3O4 (pH 7.5)
FeOOH + Fe2+ Fe3O4 + H+ (pH 9.2)
Generally speaking, under the perfect condition, co-
precipitation occurs when the mole ratio of Fe3+ to Fe2+ is
2:1. But actually, the Fe2+ is easily oxidized when ex-
posed in air, so in this paper, the mole ratio of Fe3+ to
Fe2+ is kept constant at 2:3. The whole coprecipitation
equation of Fe3+ with Fe2+ can be written in the follow-
Fe3+ + Fe2+ + 8OH Fe3O4 + 4H2O
But when the concentration of NaOH becomes 3.0
mol·L–1, slightly excessive amount of the NaOH makes
particles form partial aggregates in the sample, and in-
duces the particles increase in size. Its average size is
measured larger than that of the image recorded in Fig-
ure 3(c), as can be seen in the Figure 3(d).
It is noted that when the pH of Fe3+ and Fe2+ solution
exceeds pH of coprecipitation, the Fe3+ and Fe2+ ion all
hydrolyze much fast and have strong tendency to pre-
cipitate. And pH increases with the concentration of
NaOH increases, the excessive alkali leads to rapidly
Copyright © 2011 SciRes. MSA
Dispersibility, Shape and Magnetic Properties of Nano-FeO Particles1647
3 4
growing in size of clusters with different shapes, and
finally formation of agglomerated sphere particles in
different sizes and shapes. The higher concentration of
NaOH, the more heavily agglomeration, the results can
be seen in the Figure 3(e).
3.2. Effect of Different Water/Surfactant Molar
Ratio ( R )
The size of water-core is dependent upon water/surfacta-
nt ratio (R) [20], when R keeps constant, the size of wa-
ter-core keeps unchanged; but when R increases, the wa-
ter-core grows in size; this will lead to many topological
constructions. To study the effect of R on the dispersibil-
ity of nano-Fe3O4 particles, mole value of Fe3+ was fixed
at 0.7 mmol, mole value of Fe2+ was fixed at 1.05 mmol,
the concentration of NaOH fixed at 2.5mol/L, and R was
controlled at 3, 5, 6 and 7.
As seen from Figure 4, the four prepared samples are
heavily agglomerated shaped, local agglomerated shaped,
well uniform spherical shaped and spheroidally aggre-
gated shaped respectively. The results indicate that the
distribution of the water-core in oil phase is chiefly de-
termined by the water/surfactant molar ratio (R), the nu-
cleation and growth of hydrolyzed core is likely to be a
diffusion-controlled process through interaction between
micelles. When R = 3.0, the image of nano-Fe3O4 parti-
cles exhibit heavily agglomerated shaped with average
particle size measuring about 10 nm, because the low
water/surfactant molar ratio leads to crowded dispersion
of NP-5 in the microemulsion system, and so strong in-
teraction between micelles of NP-5. This induces wa-
ter-core contracting in the oil phase, the crystal core can
only grow in the crowded medium, and form heavily
agglomeration at last.
When R = 5.0, the increase of water/surfactant molar
ratio leads to broader dispersion of NP-5 in the microe-
mulsion system, and the water-core can be incompletely
dispersed in the oil phase. As a result, the particle size
increase, with the average size measuring about 20 nm,
and a local agglomeration is formed. When R = 6.0, wa-
ter-core is dispersed uniformly in the oil phase, and the
crystal core grows regularly, the average particle size is
measured about 22 nm, because the microemulsion sys-
tem may form well dispersive micelle.
When R = 7.0, the high mole ratio of water/surfactant
leads to a great increase in water-core size, which de-
creases the distance between neighbouring water-core,
thus leading to an increase in contractive interactions be-
tween neighbouring water-core. The crystal core grows
fast but irregularly in the uncrowded medium, and form
Figure 4. TEM images of nano-Fe3O4 particles under different R: (a) 3.0; (b) 5.0; (c) 6.0; (d)7.0.
Copyright © 2011 SciRes. MSA
Dispersibility, Shape and Magnetic Properties of Nano-FeO Particles
1648 3 4
aggregated spheroidally shaped particles.
3.3. Effect of Temperature on Magnetite
The dispersibility of magnetite is also depended upon the
temperature for preparation. When the nano-Fe3O4 parti-
cles were prepared at 30˚C, the TEM image recorded in
Figure 5(a) exhibits well dispersed particles with unif-
orm size measuring about 10 - 20 nm. Upon increasing
the synthesis temperature from 30 to 45˚C, the TEM im-
age of Figure 5(b) has lower dispersion than the cor-
responding TEM image of Figure 5(a) of the sample
prepared at 30˚C.
When the synthesis temperature continued to increase
from 45˚C to 60 and 70˚C, particles with spherical and
irregular shapes with some agglomeration are noted (Fig-
ure 5(c) and Figute 5(d)), chiefly due to rapid Brown
movement of nano-Fe3O4 particles with temperature in-
creasing. The increase in frequency of collision between
the particles leads to kinetic energy of collision increase-
ing, this makes the nano-particles have strong tendency
to overcome potential barrier between them, and ag-
glomerate into large particles, as a result, a phenomenon
of agglomeration takes place.
Throughout crystallite size variations of the nanosized
nano -Fe 3O4 particles, one can find that the particle sizes
of synthesized products are increased with the synthesis
temperature increasing, the particle sizes of synthesized
products are 15 nm, 27.5 nm, 31 nm, and 36.5 nm, cor-
responding to the synthesis temperature being 30˚C,
45˚C, 60˚C, and 70˚C respectively.
3.4. Effect of Initial Total Iron Concentration on
Magnetite Morphology
To study the effect of initial total iron concentration on
the dispersibility of nano-Fe3O4 in the microemulsion
system, R was maintained at 6.0, the concentration of
NaOH maintained at 2.5 mol·L–1, and the temperature
was kept at 30˚C. The sample was synthesized by con-
trolling initial total iron concentration at 0.63, 0.88, and
1.25 mol·L–1 (in water) respectively, while the mole ratio
of Fe3+ to Fe2+ was kept constant at 2:3.
As seen from Figure 6(a), the TEM image shows
large amount of irregular rod particles with lengths about
Figure 5. TEM images of nano-Fe3O4 particles at different temperature T: (a) 30˚C; (b) 45˚C; (c) 60˚C; (d) 70˚C.
Copyright © 2011 SciRes. MSA
Dispersibility, Shape and Magnetic Properties of Nano-FeO Particles1649
3 4
Figure 6. TEM images of nano-Fe3O4 pticles at different initial total iron concenation CFe: (a) 0.63 mol/L; (b) 0.88 mol/L
00 - 250 nm when initial total iron concentration was at
e microemulsion
as con-
onship between Magnetic f
To sdispersibility on magnetic
30˚C, while four samples A, A-2, A-3 and A-4 were
aration alkaline and total iron concentration
r the prod uc ts studied.
ntration concentration
(c) 1.25 mol/L.
0.63 mol/L, probably due to formation of β-FeOOH par-
ticles [20]. As we know, the Fe3+ ions is hydrolyzed
much faster than the Fe2+ ions in alkaline solution ac-
cording to Kθsp, Fe(OH)3 and Kθsp, Fe(OH)2, when the initial
total iron concentration is low, the mole ratio of alkaline
concentration [OH-] to initial total iron concentration
{[Fe3+] + [Fe2+]} becomes high, this induces Fe3+ ions
hydrolyzing much fast, and forming β-FeOOH particles
before coprecipitation with Fe2+ ions.
The dispersibility of nano-Fe3O4 in th
stem is also found to be dependent on the initial total
iron concentration and size of water-core. When water/
surfactant ratio (R) is constant, the size of water-core
cannot change, so dispersibility of nano-Fe3O4 are mainly
depended on the dispersion of Fe3+ and Fe2+ ions in wa-
ter-core. As seen from Figure 6(b), the TEM image
shows well uniform spherical shaped with lengths of 22
nm, probably because the Fe3+ and Fe2+ ions are dis-
persed uniformly in water-core when the initial total iron
concentration was controlled at 0.88 mol·L–1.
When the initial total iron concentration w
lled at 1.25 mol·L–1, excessive Fe3+ and Fe2+ ions may
not be dispersed uniformly in water-core. It makes the
new-formed tiny crystal core mutually collide to become
massive agglomeration before completely growing, thus
hinders the growth of the tiny core, and so results in lar-
ger sized clusters of tiny particles formation, as can be
seen in Figure 6(c). By using the Scherrer formula and
X-ray diffraction method, the particle diameter is meas-
ured to be 7 nm.
3.5. The Relati
Properties and Dispersion Behavior o
Nano-Fe3O4 Particl es
tudy the effect of particle
properties, five samples A, B, C, D and E were prepared
under different conditions with constant temperature at
prepared under different temperature conditions with
constant R, alkaline concentration and total iron concen-
tration. Listed in Table 1 are the nomenclatures we used
for different products as well as the alkaline concentra-
tion, total iron concentration and the temperature in their
Table 1. Prep
identifier R alkaline
total iron
Sample A 6.02.5 mol·L–1 0.88 mol·L–1 T =˚C 30
Sample B 6.03.0 mol·L 0.
–1 88 mol·L
–1 T = 30˚C
–1–1 C
–1–1 C
–1 –1
S–1–1 C
–1–1 C
–1–1 C
Sample C 6.03.5 mol·L 0.88 mol·L T = 30˚
Sample D 6.02.5 mol·L 0.63 mol·L T = 30˚
Sample E 6.02.5 mol·L 1.25 mol·L T = 30˚C
ample A-26.02.5 mol·L 0.88 mol·L T = 45˚
Sample A-36.02.5 mol·L 0.88 mol·L T = 60˚
Sample A-46.02.5 mol·L 0.88 mol·L T = 70˚
T metis od
able 2. Theagnc parameterf sample A, B, C, D an
SampleMs /(emu·g–1)Mr /(emu·g
–1) Mr/MsH/Oe
A 62.8 12.6 0.20 105.3
B 14.5 1.63 0.11 81.28
C 13.7 2.11 0.15 126.3
D 10.0 1.72 0.17 92.27
E 22.1 3.13 0.14 126.3
A-2 34.0 3.2 0.094 65.5
A0.-3 33.8 2.3 068 37.3
A-4 21.2 1.4 0.066 29.2
Ms: saation magnion; Mr: remanemagnetizar/Ms:re-
turetizatnt tion; M squa
Copyright © 2011 SciRes. MSA
Dispersibility, Shape and Magnetic Properties of Nano-FeO Particles
1650 3 4
Tdispersi of nanopcles wsery
ansmission electron microscope operated at 120KV,
mperature. The magnetic curves of
etization curves of sam-
pl igure 7 display magnetic
li induces the Fe and Fe ions all hydro-
th increase of total
properties and their shapes. The better dis-
and corresponding
sters. Covercivity which depends on
he bilityartias obved b
transmission electron microscopy (TEM) with a Tecnai-
12 tr
can be seen in the Figures 3(c)-(e), Figures 5(a)-(d)
and Figures 6(a)-(c). It was shown that cluster size and
cluster distribution can be influenced in a wide range
(some order of magnitude) by the variation of the prepa-
ration parameters.
Magnetic studies were carried out using a vibrating
sample magnetometer (VSM BHS-55) with fields up to
30 k Gauss at room te
e eight samples can be seen in Figure 7, all magnetic
parameters are listed in Table 2. Magnetic properties
such as saturation magnetization, coercivity and square-
ness are discussed as following.
1) Saturation magnetization
Saturation magnetization represents magnetic intensity
of magnetic materials. The magn
e A, B and C shown in the F
operties of nano-Fe3O4 particles prepared with differ-
ent alkaline concentration of 2.5, 3.0 and 3.5 mol·L–1
respectively. Whereas the magnetization curves of sam-
ple A, D and E shown in the Figure 7 display magnetic
properties of nano-Fe3O4 particles prepared with differ-
ent initial total iron concentration at 0.88, 0.63 and 1.25
mol·L–1 respectively. The magnetization curves of sam-
ple A, A-2, A-3 and A-4 shown in the Figure 7 display
magnetic properties of nano-Fe3O4 particles prepared
with different temperature at 30˚C, 45˚C, 60˚C and 70˚C
respectively. By comparing magnetic parameters of sam-
ples listed in Table 2 with their dispersibility shown in
Figures 3(c)-(e), we obtain that sample A shows the
strongest saturation magnetization, chiefly due to its
uniform size and best dispersion behavior. It is under
alkaline condition of concentration at 2.5 mol·L–1, that
coprecipitation of Fe3+ with Fe2+ ions can occur. The
saturation magnetization decreases to some extent with
gradual increase of NaOH concentration from 2.5 mol·L–1
to 3.5 mol·L–1. Because the nano-Fe3O4 particles change
from well-dispersed into partial aggregate, and finally
heavily agglomerate, with an increase of alkaline con-
The better dispersibility of nanoparticles can be ex-
plained by the size of clusters with uniform shape. Ex-
cessive alka3+ 2+
zing much fast, leads to nanoparticles rapidly changing
into larger sized clusters with arbitrary smaller shaped
particles. The better dispersibility of nanoparticles, the
stronger magnetic behavior of them [21]. This means
inner magnetic vector becomes more ordered, with an in-
crease of dispersion of nanoparticles, and thus the nano-
particles display stronger magnetism, leading to an in-
crease of saturation magnetizationσs.
When different initial total iron concentration was
adopted during preparation, the saturation magnetization
of particles is found to be stronger wi
n concentration. For sample D, the total iron concen-
tration is so low that Fe3+ ions hydrolyzed faster than
Fe2+ ions and formed β-FeOOH particles before copre-
cipitation with Fe2+ ions. This would lead to decrease of
its saturation magnetization. In the opposite side, when
the total iron concentration was higher than 0.88 mol·L–1,
coprecipitation of Fe3+ with Fe2+ ions occurs, this pre-
vents β-FeOOH particles from generating, causing an
increase of saturation magnetization σs of sample E. But
mutually collision between new-formed tiny crystal cores
hinders the growth of the tiny core, leading to formation
of larger sized clusters with different tiny shapes. So
dispersibility of nanoparticles of sample E is worse than
that of sample A, inner magnetic vector becomes less
ordered also, as a result, the saturation magnetization σs
of sample E becomes lower than that of sample A.
By comparing magnetic parameters of samples listed
in Table 2 with their dispersibility shown in Figures 5
(a)-(d), we obtain that sample A shows the stro
turation magnetization, also chiefly due to its uniform
size and best dispersion behavior. When the nano-Fe3O4
particles were prepared at 30˚C, the sample A was ob-
served to have the best dispersibility, when the tempera-
ture increased from 30˚C to 70˚C, the dispersibility of the
sample A-2, sample A-3 and ample A-4 decreased stead-
ily, resulting in inner magnetic vector getting less or-
dered [21], and thus a progressive decrease in the satura-
tion magnetization σs for sample A-2, sample A-3 and
sample A-4.
The above results demonstrate that saturation mag-
netization of nano-Fe3O4 particles is greatly influenced
by dispersion
rsed nano-Fe3O4 particles with more uniform and dis-
persed shapes will have higher saturation magnetization,
and thus display stronger magnetism.
2) Coercivity
Coercivity of magnetic matericals mainly depends on
anisotropy, saturation magnetization
ructure paramet
agneto-crystalline anisotropy can be expressed by the
following formula according to Zhou.[22]:
cK Ms
In this formula, K value depends only on property of
material itself, but not related to particle size and shape,
it is inversely proportional to saturation magnetization.
As seen from Table 2, coercivity of sample A is higher
than that of sample B and D, but lower than that of sam-
ple C and sample E.
Copyright © 2011 SciRes. MSA
Dispersibility, Shape and Magnetic Properties of Nano-Fe3O4 Particles
Copyright © 2011 SciRes. MSA
-15000 -10000-5000050001000015000
Sample (A)
-2000 -1000010002000
Sample (B)
-2000 -1000010002000
Sample (D)
-2000 -1000010002000
Sample (C)
-15000 -10000-5000050001000015000
Sample (A-2)
-2000 -1000010002000
Sample (E)
He/ Oe
-15000 -10000-5000050001000015000
Sample (A-3)
-15000 -10000-5000050001000015000
Sample (A-4)
Figure 7. Magnetization hysteresis curves of nano-Fe3O4 particles synthesized under differe nt conditions.
Dispersibility, Shape and Magnetic Properties of Nano-FeO Particles
1652 3 4
According to the formula, sample A should have the
lowest coercivity compared with other samples because
of its highest saturation magnetization. However, it is
found that there is no such obvious linear relationship
between coercivity and saturation magnetization. The
coercivity of particles is related to their size of clusters
and shapes. It is noted that coercivity decreased with
reduction of particle size below 40nm [23]. As shown in
Figures 3(d)-(e) and Figures 6(a)-(c), sample A shows
well uniformly spherical shaped with lengths of 22 nm,
but both of samples C and E display large size of clusters,
but consisting of smaller size particles than sample A. So
both of samples C and E show larger coercivity than
mple A
. On the other hand, average size of sample B is
rger than that of sample A, and sample D is 100 - 250
nm length irregular rod particles, these all lead to sample
A having a larger coercivity than the sample B and D.
As shown in Figures 5(a)-(d), with an increase of
temperature from 30˚C to 70˚C, the dispersibility of the
sample decreased progressively, resulting in the coer-
civeity of sample decreasing. A plot of coercivity versus
the temperature is shown in Figure 8, the Figure 8
shows linear relationship between coercivity and tem-
perature. It demonstrates that the temperature has signi-
ficant influence on the anisotropy and dispersibility of
the sample, with an increase of temperature, the anisot-
ropy and dispersibility of the sample decreases, leading
to coercivity decreasing.
3.6. Ind e xing t he Powder X - R ay Di f f r acti o n
The results of indexing the powder X-ray diffraction pat-
tern are listed in Table 3 . Table 3 shows that all the dif-
fraction peaks in the pattern can be readily indexed by
one set of lattice parameters. The largest relative devia-
tion between the calculated Dcal and experimental Dexp is
less than 0.347%, which indicates that the synthesized
products are a single phase with cubic structure. The
30 40 50 60 70
Temperature oC
civity Oe
Temperature ˚C
Figure 8. Plot of coercivity versus the temperature.
Table 3. The experimental data and the calculated results
for powder X-ray diffraction pattern of the nano-Fe3O4
particles cubic system: a = 8.273 Å.
Dexp (Å) Dcal (Å)h k lI(%)Dexp (Å) Dcal (Å) (nm)h k lI(%)
2.84302.92492201001.4846 1.4625 4 4 01.89
2.52662.49443113.711.4113 1.3081 6 2 04.33
1.99772.06824 0018.911.2622 1.2472 6 2 23.08
1.70081.68874 2 21.271.1522 1.1055 6 4 21.89
1.62871.59215 1 13.71
ty O
crystal structure of synthesized product belong
cubic system.
s to the
4. Conclusions
In summary, the cubic nano-Fe3O4 particles have been
successfully synthesized by using two-step microemul-
sion method. The dispersibility, shape and anisotropy of
nano -Fe 3O4 particles vary with R value, alkali concentra-
tion, and the temperature. The prepared nano-Fe3O4 par-
ticles all exhibits dispersive spherical form with well
uniform sizes measured about 22 nm under condition of
R = 6.0, alkali concentration at 2.5 mol/L, with the tem-
perature at 30˚C. Magnetic properties are influenced
greatly by dispersibility and shape of particles. The crys-
tal structure of the nano-Fe3O4 particles belongs to cic
ence Foundation of Ch-
ina (No: 20971043), and the nancial support from Wen-
z e)
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We thank the National Natural Sci
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