Synthesis and magnetic properties of Y3-xDyxFe5O12 nanoparticles

Article abstract of DOI:10.1016/j.jmmm.2006.02.095

Dy³⁺-substituted garnet nanoparticles Y_3-xDy_xFe₅O₁₂ (x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) were fabricated by a sol-gel method and their crystalline structures and magnetic properties were investigated by using X-ray diffraction (XRD), infrared spectroscopy and vibrating sample magnetometer (VSM). The XRD patterns of Y_3-xDy_xFe₅O₁₂ have only peaks of the garnet structure and the sizes of particles range from 37 to 63 nm. Results of VSM show that the saturation magnetization of Y_3-xDy_xFe₅O₁₂ (0 < x ≤ 1) particles is not only obviously less than pure Yttrium iron garnet, but also decreases with increasing the Dy concentration (x) in a linear manner. Meanwhile, it is observed that with the enhancement of the surface spin effects, the saturation magnetization rises as the particle size is increased.

Full text of DOI:10.1016/j.jmmm.2006.02.095

ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 308 (2007) 5–9
www.elsevier.com/locate/jmmm
Synthesis and magnetic properties of Y Dy Fe O nanoparticles
x
3ꢀx
5 12
a
a,
Ã
a
Zhongjun Cheng , Hua Yang , Yuming Cui , Lianxiang Yu ,
a
b
Xueping Zhao , Shouhua Feng
c
a
College of Chemistry, Jilin University, Changchun 130023, PR China
b
College of Physics, Jilin University, Changchun 130023, PR China
c
State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, Changchun 130023, PR China
Received 18 October 2005; received in revised form 2 February 2006
Available online 6 March 2006
Abstract
3
+
Dy -substituted garnet nanoparticles Y3ꢀxDy
x
Fe
5
O
crystalline structures and magnetic properties were investigated by using X-ray diffraction (XRD), infrared spectroscopy and vibrating
12 (x ¼ 0, 0.2, 0.4, 0.6, 0.8 and 1.0) were fabricated by a sol–gel method and their
sample magnetometer (VSM). The XRD patterns of Y3 Dy Fe O have only peaks of the garnet structure and the sizes of particles
5
ꢀx
x
12
range from 37 to 63 nm. Results of VSM show that the saturation magnetization of Y3ꢀxDy
x
Fe
5
O
12 (0oxp1) particles is not only
obviously less than pure Yttrium iron garnet, but also decreases with increasing the Dy concentration (x) in a linear manner. Meanwhile,
it is observed that with the enhancement of the surface spin effects, the saturation magnetization rises as the particle size is increased.
r 2006 Elsevier B.V. All rights reserved.
PACS: 75.50; 81.05; 81.16; 72.15.L; 07.85.F; 68.37.R; 65.80
Keywords: Magnetization; YIG; Rare earth Dy ions
1
. Introduction
because of the unique magneto-optical property of YIG,
researchers have done a lot of work and succeeded in
3
+
3+
3+
3+
substituting Bi and Ce for Y , and Co and Co
2+
Yttrium iron garnet (YIG) is a ferromagnetic material
3
+
which is extensively used in optical communication and
magneto-optical devices [1,2]. Ferromagnetic garnets are
assigned to cubic structure (space group Ia3d), every cell
contains eight R Fe5 O12 molecules, and the ion
distribution structure can be represented by writing the
garnet formula as {R }[Fe ](Fe )O ; { }, [ ] and ( ) are
for Fe in YIG so as to obtain materials with different
magneto-optical properties.
When YIG is prepared by ceramic methods, YFeO and
3
3
3
+
3+
Fe O are produced as intermediates and these phases
2
3
remain as impurities unless heated to high temperatures
[6,7], so the sol–gel method has attracted attention due to
the lower synthesis temperature and finer and more
homogeneous particles produced. A systematic study of
the sol–gel technique for the synthesis of Y Fe O is
3
2
3
12
represented for 24c (dodecahedral), 16a (octahedral) and
4d (tetrahedral), respectively. YIG is the most represen-
2
tative and well-known compound among the rare earth
iron garnets [3], and the various magnetizations can be
achieved by substitution in the YIG [4]. Thongmee and
Winotai [5] studied the magnetic properties of dilution of
3
5
12
presented by Vaqueiro [3,8], and the results show that the
citric is a suitable chelating agent to obtain the fine
particles, which exhibit a rounded surface morphology and
are without faceted borders. Meanwhile, YIG could be
formed by a single-step process, where an amorphous
precursor powder is formed first and then transformed
to YIG during calcination, without any intermediate
phase formation. The experimental results [9,10], obtained
using the sol–gel method, indicate that the saturation
3
+
3+
the Fe by Al in the substituted Y Fe Al O . They
12
3
5ꢀx
discovered that the saturation magnetization and coercivity
x
3+
both decreased in samples containing Al . Furthermore,
Ã
Corresponding author. Tel.: +86 431 8499151; fax: +86 431 5095011.
E-mail address: huayang86@sina.com (H. Yang).
0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmmm.2006.02.095

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Z. Cheng et al. / Journal of Magnetism and Magnetic Materials 308 (2007) 5–9
6
magnetizations of Ce:YIG and La:YIG materials are
different from pure YIG. Furthermore, Leleckaite and
Kareiva use the sol–gel method to prepare rare earth-
doped yttrium aluminum garnets YAG:Ln (Ln ¼ Ce, Nd,
Ho and Er),which are important solid-state laser materials
widely used in luminescence systems, window materials for
a variety of lamps and fiberoptic telecommunication
systems [11].
X=1.0
X=0.8
X=0.6
In this article, we substituted the magnetic rare earth ion
3
+
3+
Dy
for some non-magnetic ions Y
in YIG, and
prepared Y3ꢀx
Dy Fe O (x ¼ 0, 0.2, 0.4, 0.6, 0.8 and 1.0)
x
5
12
X=0.4
nanoparticles using a sol–gel method. At the same time, the
crystalline size and magnetic properties were observed and
studied in detail.
X=0.2
X=0.0
2
. Experiment
A stoichiometric mixture of Fe(NO ) , Dy(NO ) ,
3
3
3 3
Y(NO ) (Dy O and Y O were dissolved in HNO ) was
3
3
2
3
2
3
3
2
0
25
30
35
40
45
50
55
60
65
dissolved in an aqueous solution of citric acid, and then
NH ꢁ H O was added to adjust pH ¼ 2. The resulting
2-theta
3
2
solution was heated at 353 K in order to obtain the gel; to
obtain the Y3 Dy Fe O samples, the gels were dried
initially at 383 K for 36 h and further heat treated in air
Fig. 1. XRD of samples with Dy concentration (x) from x ¼ 0 to 1,
treated at 1073 K for 3 h.
ꢀx
x
5
12
between 1023 and 1373 K for 3 h.
The structure and the crystallite sizes were tested by
X-ray diffractometer (SHIMADZU Co., Tokyo, Japan) in
the 2y range 25–601 using CuKa radiation (l ¼
0
:15405 nm), and the crystallite sizes of the samples are
estimated from the line width of the (4 2 2) XRD peaks.
The infrared (IR) spectra were recorded as KBr pellets on
Perkin–Elmer Spectrum One FT/IR spectrometers.
1373K
Magnetic measurements were carried out at room
temperature using a vibrating sample magnetometer
(VSM; Digital Measurement System JDM-13) with a
maximum magnetic field of 10 000 Oe.
1
1
273K
073K
3
3
3
. Results and discussion
.1. Structure characterization
1
023K
.1.1. X-ray diffraction
Fig. 1 shows XRD of samples with Dy concentration (x)
from x ¼ 0 to 1 treated at 1073 K for 3 h. Through Fig. 2,
20
25
30
35
40
2-theta
45
50
55
60
65
the evolution of the crystalline phase of Y DyFe O was
12
2
5
investigated as a function of heating temperature, and the
treating temperatures are from 1023 to 1373 K. From these
XRD patterns ,one can observe that all samples have only
a single phase of garnet structure and crystallization occurs
around 1023 K, which is lower than the 1573 K used in the
ceramic method [6]. This lower crystallization temperature
could be related to the good homogeneity of the gel
prepared at pH ¼ 2. At the same time, one can observe
that the crystallization of samples is more complete as the
annealing temperature is increased.
Fig. 2. XRD patterns of Y
373 K.
2 5
DyFe O12, samples heated from 1023 to
1
tration (x) but treated at different temperature. The
obtained sizes increase as the heating temperature is
increased from 1073 to 1373 K (Fig. 3). Furthermore, we
can also observe that for similar annealing, the crystallite
sizes of Y3 Dy Fe O (0pxp1) are similar to each other
ꢀx
x
5
12
According to the Scherrer’s relationship, we calculated
the crystalline sizes for samples with the same Dy concen-
and the variation has no apparent regularity (Fig. 4).
The phenomenon is probably due to the similar ionic

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Z. Cheng et al. / Journal of Magnetism and Magnetic Materials 308 (2007) 5–9
7
6
6
5
5
4
4
3
5
0
5
0
5
0
5
1
1
073k
023k
673k
573k
x=0.0
x=0.2
x=0.4
x=0.6
x=0.8
x=1.0
as-obtained
1050 1100 1150 1200 1250 1300 1350 1400
T (K)
4
000
3500
3000
2500
2000
1500
1000
500
-1
Wave number(cm )
Fig. 3. Dependence of particle size on the heating treatment for samples
Fe
12 (x ¼ 021).
Y3ꢀxDy
x
5
O
5
Fig. 5. IR spectra of Y2.6Dy0.4Fe O12 treated at different temperatures.
9
8
8
7
7
6
6
5
5
4
4
3
3
2
2
1
1
0
5
0
5
0
5
0
5
0
5
0
5
0
5
0
5
0
ꢀ
1
1
1
073k
273k
and 1200 cm , which can be assigned to the vibrations of
carboxylic groups. However, the bands at 1726 and
ꢀ
1
1200 cm
disappear when the precursor is calcined at 573 K. A new
decrease with the heating procedure and
1373k
ꢀ
1
band, at 1520 cm , together with the one at 1400 cm
ꢀ1
,
can be assigned to ionized carboxylates and carbonates
[
12]; at the same time two other new bands, at 1080 and
ꢀ
1
50 cm , can also be assigned to carbonates; all these
8
are results of the rupture of citrate molecules. Moreover,
ꢀ
1
there is another band at 2340 cm , assignable to CO2
decreases, and disappears as the annealing temperature is
increased [13].
IR spectra of samples heated at 673 and 873 K exhibit
ꢀ1
bands at 1520, 1400, 1080 and 850 cm
assigned to
carbonates [11]. The intensity of these bands decreases with
higher calcination temperature. IR spectra of samples
heated at 1023 K exhibit the bands assigned to carbonates,
but with lower intensity than before. However, a broad
0.0
0.2
0.4
0.6
0.8
1.0
Dy (x)
ꢀ1
band appears at 565 cm , assignable to vibrations of the
Fig. 4. Dependence of particle size on the Dy concentration (x) for
samples treated at different temperatures.
group Fe–O [3,11], which indicates that crystallization
occurs at 1023 K and this is in accord with the result of
XRD. IR spectra of samples annealed at 1073 K do not
show any band assigned to carbonates, and the broad band
3
+
3+
ꢀ1
˚
˚
radius of Dy (0.908 A) to Y (0.892 A), which leads to
no apparent variation about the crystalline lattice. Thus
samples with the Dy concentration (x) from 0.0 to 1.0 have
similar particle sizes in the same heating treatment.
at 565 cm is replaced by three bands at 660, 600 and
ꢀ
1
565 cm , assignable to the stretching mode of the
tetrahedron in Y2.6Dy0.4Fe O [3,6,14], and this indicates
5
12
that the crystallization of samples is more complete as the
annealing temperature is increased.
3
.1.2. IR spectra
IR spectra of Y2.6Dy0.4Fe O were recorded for the
From IR measurement, one can conclude that the citrate
structure is broken down at 573 K, but some carbonates
remain until 1023 K. Meanwhile, the crystallization occurs
around 1023 K, and with increasing the heating treatment
temperature the crystallization of samples becomes more
complete. All these results are consistent with those
obtained by XRD.
5
12
precursor as obtained and after calcinations at 573 K. As
illustrated in Fig. 5, two bands appear at 3400 and
1
and can be assigned to water [3]. In the spectra of the
precursor as obtained, three bands appear at 1726, 1400
ꢀ
1
640 cm
which decrease with drying and calcinations

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Z. Cheng et al. / Journal of Magnetism and Magnetic Materials 308 (2007) 5–9
8
3
3
.2. Magnetization
represented by writing the garnet formula as {Y3 Dyx}
ꢀx
[
sub-lattice). Because Dy
magnetic, whose magnetic moment is 10.6 A m (Y ion is
non-magnetic and its magnetic moment is 0), so there are
Fe ](Fe )O ({ } ¼ c sub-lattice, [ ] ¼ a sub-lattice, ( ) ¼ d
2
3
12
3
+
.2.1. Saturation magnetization (Ms) vs. particle size (D)
In Fig. 3, one can observe that the crystallite sizes of
ions in Y Dy Fe O are
3ꢀx x 5
12
3+
2
samples with the same Dy concentration (x) increase as the
heating temperature is increased. Fig. 6 shows the variation in
saturation magnetization (Ms) at room temperature with the
average particle size when the concentrations (x) of Dy are 0,
3
+
three magnetic sub-lattices: one (c) formed by the Dy
ions occupying the dodecahedral sites, another (a) formed
3
+
by Fe ions occupying the octahedral sites and the third
3
+
0.2, 0.4, 0.6, 0.8 and 1.0. From Fig. 6, one can conclude that
(d) formed by the Fe
ions occupying the tetrahedral
for samples with the same Dy concentration (x), the saturation
magnetization (Ms) rises with increasing the particle size. For
example, when x ¼ 0:2, the crystallite sizes are 42.2, 51.3 and
sites. The two iron sub-lattices are coupled anti-ferromag-
netically by the super-exchange interaction acting via the
2
ꢀ
intervening O ions. The c sub-lattice is coupled anti-
ferromagnetically with the tetrahedral sub-lattice. At room
temperature, the three sub-lattice moments align along the
[1 1 1] direction. Therefore, the magnetic structure for such
a mixed garnet can be represented by writing the garnet
formula as
6
0.0 nm at different temperatures; accordingly, the saturation
magnetizations (Ms) are 24.1, 24.7 and 25.8 emu/g, respec-
tively. A similar reduction in the magnetization was observed
in small particles of iron [15], g-Fe O [16], BaFe O [17] and
2
3
12 9
MnFe O [18]. This reduction can be related to the higher
2
4
surface-to-volume ratio in the smaller particles, which results
in the existence of non-magnetization surface layer; therefore,
the saturation magnetization (Ms) of the particles decreases as
the particle sizes reduce.
and the net magnetic moments is M ¼ Mcꢀ|MdꢀMa|.
In the case of Y Dy Fe O , the variation in satura-
12
3
ꢀx
x
5
tion magnetization (Ms) with the Dy concentration (x) is
shown in Fig. 7, where three lines are represented for
samples prepared at 1073, 1273 and 1373 K. From Fig. 7,
one can conclude that the saturation magnetization (Ms)
decreases with increasing Dy concentration (x) in a linear
manner, which could be related to the fact that the
3
(
.2.2. Saturation magnetization (Ms) vs. Dy concentration
x)
The garnet crystal lattice can be represented as a
framework of metal–oxygen polyhedron. Each tetrahedron
is connected to four octahedra, while each octahedron is
linked with six tetrahedra. These corner-shared units are
slightly distorted, their network forms dodecahedral
cavities. In YIG, all the tetrahedral and octahedral cavities
are occupied by Fe and dodecahedral cavities are
+
occupied by Y . In this experiment, we substituted some
Dy
3
+
magnetic moments of Dy
effective moments formed by Fe ions.
ions align opposite to the
3
+
3
+
4. Conclusions
3
3
+
3+
for Y , so the ion distribution structure can be
In conclusion, we have studied the synthesis and magnetic
properties of Y3 Dy Fe O nanoparticles, with size
5 12
ꢀx
between 37 and 63nm, prepared using a sol–gel method.
x
2
8
6
4
2
0
8
From the XRD and IR data, we observe that all the samples
x=0
2
2
2
2
2
2
2
2
2
2
1
1
1
8
7
6
5
4
3
2
1
0
9
8
7
1
1
1
073k
273k
373k
x=0.2
x=0.4
2
2
2
1
x=0.6
x=0.8
x=1.0
35
40
45
50
55
60
65
0.0
0.2
0.4
0.6
0.8
1.0
D (nm)
Dy (x)
Fig. 6. Variation in saturation magnetization (Ms) with the average
particle size (D, nm).
Fig. 7. Variation in saturation magnetization (Ms) with the Dy
concentration (x).

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Z. Cheng et al. / Journal of Magnetism and Magnetic Materials 308 (2007) 5–9
9
have only a single phase of garnet structure, and the
crystallization begins around 1023 K. Furthermore, the
crystallite size obtained increases with increasing the heating
temperature. Results of magnetic properties tell us that for
samples with the same Dy concentration (x), the saturation
magnetization (Ms) decreases as the particle size is reduced
due to the enhancement of the surface spin effects [19].
[5] S. Thongmee, P. Winotai, Solid State. Commun. 109 (1999) 471.
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47.
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(
[
[
[
2
´
pez-Quintela, J. Solid
3+
Meanwhile, because the magnetic moments of Dy
ions
[10] C. S. Kim, Y.R. Uhm, S Kim, J.-G. Lee, J. Magn. Magn. Mater
215–216 (2000) 551.
3
+
align opposite to the effective moments formed by Fe ions,
one can conclude that the saturation magnetization (Ms)
linearly decreases as the Dy concentration (x) is increased.
[
[
11] A. Leleckaite, A. Kareiva, Opt. Mater. 26 (2004) 123.
12] B.M. Gatehouse, S.E. Livingstone, R.S. Nyholm, J. Chem. Soc. 4
(
1958) 3137.
[
13] B. Schrader, Infrared and Raman Spectroscopy. Methods and
Acknowledgements
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[
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This work was supported by the National Natural
Science Foundation of China (NNSFC).
(
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[
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[
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