Investigating the formation and magnetic properties of the Dy0.75Fe1.25O3 orthoferrite prepared by sol-gel method

Article abstract of DOI:10.1016/j.jmmm.2009.07.080

In this paper, the Dy_0.75Fe_1.25O₃ orthoferrite nanoparticles were synthesized successfully by sol-gel method. Dy_0.75Fe_1.25O₃ orthoferrite nanoparticles are obtained by calcining the flakes

Full text of DOI:10.1016/j.jmmm.2009.07.080

ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 321 (2009) 3997–4000
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Journal of Magnetism and Magnetic Materials
journal homepage: www.elsevier.com/locate/jmmm
Investigating the formation and magnetic properties of the Dy0.75Fe1.25 3
O
orthoferrite prepared by sol–gel method
a,Ã
b
Jian-Jun Li , Jun-Gang Cao
a
Centre for Composite Materials and Structures, Harbin Institute of Technology, Harbin 150001, People’s Republic of China
College of Chemistry, Jilin University, Changchun 130012, People’s Republic of China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
In this paper, the Dy0.75Fe1.25O3 orthoferrite nanoparticles were synthesized successfully by sol–gel
method. Dy0.75Fe1.25O3 orthoferrite nanoparticles are obtained by calcining the flakes at 600 and 700 1C.
The magnetic properties of the different samples are investigated using Quantum Design MPMS SQUID
Received 27 April 2009
Received in revised form
16 July 2009
magnetometer and MS-500 M o¨ ssbauer spectrometer. Magnetic phase
2 3
g-Fe O coexists in the samples
Available online 12 August 2009
calcined at 600 1C and orthoferrite phase is completely recovered in the samples calcined at 700 1C.
3
+
3+
PACS:
Although excessive Fe ions were introduced, none of these iron spins couple magnetically with Dy
ions.
7
5.50.Tt
76.30.Kg
&
2009 Elsevier B.V. All rights reserved.
Keywords:
Orthoferrite nanoparticle
Difference curve
M o¨ ssbauer spectra
1
. Introduction
netic state [13]. At low temperature, several of the rare-earth
orthoferrites exhibit a further spin order which is related to the
3
+
The compounds of RFeO
3
(R ¼ rare earth) are important
rare-earth ions themselves and the ordered Fe lattices will
reorientate. In recent years, nanocrystalline orthoferrite RFeO
magnetic oxides which exhibit special magnetic and magnetic-
optical properties [1–5]. In the 1950s and 1960s, these magnetic
oxides attracted many scientists’ research interest, especially the
3
have been prepared by different methods [14–16]. For preparing
rare-earth orthoferrites at relatively low temperature, bimetallic
precursors approach is always used to replace solid station
reaction method. Normally the bimetallic precursors approach is
a little complicated and the traditional sol–gel method involves
the hydrolysis of metal alkoxides. But in this paper we will use a
simple, low-cost and effective sol–gel method to prepare Dy
magnetic properties of the RFeO
3
orthoferrite single-crystal.
Investigation into these compounds will be favorable not only
for understanding the nature of magnetic interactions in struc-
tures of this type but also for their applications. The crystal
structure of RFeO
RFeO has a distorted perovskite structure with four molecular
3
compounds has been reported by Geller [6,7].
3
+
orthoferrite nanoparticles and introduce excessive Fe
into
3
3
+
units per unit cell. Magnetic properties were studied and neutron-
diffraction measurement was also made on the orthoferrite family
reactive system to replace some Dy ions. We will have a better
understanding of the nature of magnetic interactions in structures
of this type and the applications of rare-earth orthoferrites by
investigating its magnetic properties.
[
8,9]. Double rare-earth orthoferrite were synthesized and
characterized by M o¨ ssbauer spectrometer [10]. In a series of
rare-earth orthoferrite compounds, there exists three allowed spin
configuration. All the spin configurations consist of variations of a
canted antiferromagnetic alignment of Fe magnetic moments.
The first spin configuration is called (F ) configuration where
3+
2. Experimental
G
4
z
the net magnetic moment aligns along the c-axis [11,12], and the
net magnetic moment aligning along the a-axis means the second
Fe(NO
reagents. For the preparation of Dy0.75Fe1.25
Fe(NO O and citric acid were mixed in a reaction vessel
ꢀ 9H
containing distilled water under vigorous stirring, and Dy was
put in the diluted hydrochloric acid under water-bath conditions
till Dy was dissolved completely. The prepared DyCl solution
was added into the previous mixed solution stoichiometrically.
3
)
3
ꢀ 9H O, Dy
2
2
O
3
and citric acid were used as the initial
O
3
nanoparticles,
configuration
G
2
(F
x
). The last spin configuration
1
G (0) has been
3
)
3
2
proposed for the Dy orthoferrite which has a fully antiferromag-
2 3
O
Ã
O
Corresponding author.
2
3
3
E-mail address: ljj8081@tom.com (J.-J. Li).
0304-8853/$ - see front matter & 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmmm.2009.07.080

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J.-J. Li, J.-G. Cao / Journal of Magnetism and Magnetic Materials 321 (2009) 3997–4000
Then the resulting solution was evaporated to form a gel, which
was subsequently dried at 100 1C for a certain time in an oven
until it broke into brittle flakes. Finally the flakes were calcined at
oxygen atmosphere, and the orthoferrite nanoparticles with
uniform sizes were obtained.
18
FC
ZFC
1
1
6
4
The powder X-ray diffraction (XRD) patterns of the magnetic
nanoparticles were obtained on a Siemens D5005 X-ray diffract-
˚
ometer with CuK
ZFC and FC curves of the samples were characterized by using a
Quantum Design MPMS SQUID magnetometer. The
a radiation (l ¼ 1.5418 A). The hysteresis loop,
12
5
7
Fe
M o¨ ssbauer spectroscopic experiments were conducted on a MS-
1
0
8
6
57
5
00 M o¨ ssbauer spectrometer using Co source in a rhodium
matrix, whereas -Fe was used for calibration.
a
3
. Results and discussion
0
50
100
150
200
250
300
350
400
Fig.
1
shows powder X-ray diffraction pattern for the
orthoferrite samples calcined at 600 1C (a) and
00 1C (b), respectively. We can easily see that the positions of the
Temperature (K)
Dy0.75Fe1.25O
3
6
5
4
3
2
1
0
7
FC
XRD peaks coincide exactly with the standard ones reported in the
literature [13,17]. When the brittle flakes were calcined at 600 1C,
the samples show a poor crystallization, only the main peak is
observed. The peak at around 35.551 (indicated by red line in Fig.
(a) reveals the coexistence of
the X-ray diffraction peaks of Dy0.75Fe1.25
nanoparticles appear and the intensity of peak at around 35.551
becomes very small. It is evident that the higher calcination
temperature favors the formation of Dy0.75Fe1.25
nanoparticles.
ZFC
1
g-Fe
2
O
3
. After heated at 700 1C, all
orthoferrite
O
3
3
O orthoferrite
Fig.
2
displays the temperature dependence of the
magnetization under a magnetic field of 200 Oe for zero-field-
cooled (ZFC) and field-cooled (FC) samples calcined at 600 and
00 1C, respectively. In the FC measurement, the obtained
magnetic nanoparticles are cooled to 4 K under a 200 Oe applied
magnetic field and the magnetization measurement is recorded
from 4 to 300 K with the applied field unchanged. But in the ZFC
measurement, the obtained samples are cooled from room
temperature to 4 K under a zero magnetic field. From the
results, we clearly know that the ZFC and FC curves for
7
0
50
100
150
200
250
300
350
400
Temperature (K)
Fig. 2. (Color online) The ZFC–FC curves recorded at 200 Oe for the Dy0.75Fe1.25O3
orthoferrite samples calcined at 600 1C (a) and 700 1C (b) ( : FC, : ZFC).
J
Dy0.75Fe1.25
O
3
orthoferrite nanoparticles obtained at 600 1C show
little difference. The similar shapes of ZFC and FC curves in
Fig. 2(a) indicate that the Dy0.75Fe1.25 orthoferrite nanoparticles
2 4
are not sensitive to initial cooling progress unlike AB O spinel
O
3
ferrites [18]. We think that the prepared orthoferrite nanoparticles
have strong anisotropy and the applied magnetic field during
cooling cannot overcome it. In Fig. 2(b), there is a little difference
between FC and ZFC curves in the temperature range from 20 to
60 K. Such difference can be explained by the facts. In the ZFC
curve, the magnetic moments of the rare-earth ions become
disordered and spin reorientation of ordered iron lattices occur in
the temperature range from 20 to 60 K. While in the FC curve, due
to the applied magnetic field during cooling, the spin
reorientation of ordered iron lattices does not happen. For the
samples obtained at 600 1C, such spin reorientation is not
observed for the poor crystallization of synthesized samples.
The magnetic moment decreases with increasing temperature
which is in accordance with the results reported [2]. At
temperatures below 20 K, the moments of the rare-earth ions
are ordered and the exchange interaction will play an important
role [19] which accounts for the large magnetization in the low
temperature. With temperature increasing, the moments of the
rare-earth ions become disordered and the magnetization will
decrease sharply due to thermal activation. At the lowest
measuring temperature, the magnetization can be as high as
(
(
b)
a)
20
30
40
50
-Theta (degrees)
60
70
80
2
1
8 emu/g for samples calcined at 600 1C, while only 5.5 emu/g for
Fig. 1. The powder X-ray diffraction pattern for the Dy0.75Fe1.25
samples calcined at 600 1C (a) and 700 1C (b). The red line for peak labeling
indicates the coexistence of -Fe
3
O orthoferrite
3
+
samples calcined at 700 1C. Although excessive Fe ions were
introduced, none of these irons spins couple magnetically with
g
2
O
3.

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J.-J. Li, J.-G. Cao / Journal of Magnetism and Magnetic Materials 321 (2009) 3997–4000
3999
3+
Dy ions [20,21]. The net magnetic moment of Dy0.75Fe1.25
O
3
2 3
magnetic phase g-Fe O , so the sample with poor crystallization
orthoferrite nanoparticles is caused by the slight canting of iron
magnetic moments. The samples calcined at 600 1C contain
has high magnetization and higher crystallization (calcined at
700 1C) leads to the smaller magnetization. The decrease in the
magnetic moment results from the increase in the relative volume
of the orthoferrite phase. The magnetic moments of orthoferrite
phase are significantly smaller than that of magnetic phase
Fe
g-
3
2
1
0
0
0
0
2 3
O .
a
b
In Fig. 3 we show the hysteresis loops, measured at room
temperature, for the samples calcined at 600 1C (a) and 700 1C (b).
The magnetization of the samples calcined at 600 1C increases
sharply under smaller magnetic field, which means that magnetic
phase
g
-Fe
2
O
3
coexists. Then the magnetization increases
smoothly with increasing magnetic field. For the samples
calcined at 700 1C, the magnetization always increases smoothly
with magnetic field increasing, indicating the hard magnetic
3
feature of Dy0.75Fe1.25O nanoparticles. Let us look at the
-
-
-
10
20
30
difference between the ascending (points going from negative
magnetic field to positive magnetic field) and descending (points
going from positive magnetic field to negative magnetic field)
portions of the hysteresis loop by subtracting their values of
magnetic moment for the various value of magnetic field [13,22].
The obtained results (named as difference curve) for the samples
calcined at 600 1C (a) and 700 1C (b) are displayed in Fig. 4,
respectively. The central peak in Fig. 4(a) is attributed to the
6.0x104 -4.0x104 -2.0x104
2.0x104 4.0x104 6.0x104
-
0.0
H (Oe)
magnetic phase
2 3
g-Fe O in the prepared samples, while in
Fig. 3. Hysteresis loops for the orthoferrite samples calcined at 600 1C (a) and
7
00 1C (b).
Fig. 4(b) the central peak becomes very small. The smaller
central peak in Fig. 4(b) is due to the increase in the relative
volume of the orthoferrite phase.
Rare-earth orthoferrites have been studied by M o¨ ssbauer
spectroscopy [23,24]. To investigate the magnetic properties
further, we got the M o¨ ssbauer spectra (shown in Fig. 5) of the
5
4
3
2
1
0
100
9
9
9
9
9
8
7
6
-
-
1
6.0x104 -4.0x104 -2.0x104
0.0
H (Oe)
2.0x104 4.0x104 6.0x104
-9
-6
-3
0
3
6
9
5
4
3
2
1
0
Velocity (mm/s)
1
00
9
9
98
9
9
9
7
6
5
-
-
1
6.0x104 -4.0x104 -2.0x104
0.0
2.0x104 4.0x104 6.0x104
-9
-6
-3
0
3
6
9
H (Oe)
Velocity (mm/s)
Fig. 4. Difference curves for the orthoferrite samples calcined at 600 1C (a) and
00 1C (b). Data are taken from Fig. 3 and line is a guide to the eye.
Fig. 5. (Color online) The M o¨ ssbauer spectra of orthoferrite samples calcined at
600 1C (a) and 700 1C (b) recorded at room temperature.
7

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J.-J. Li, J.-G. Cao / Journal of Magnetism and Magnetic Materials 321 (2009) 3997–4000
Table 1
M o¨ ssbauer parameters of samples calcined at 600 and 700 1C.
ties. Using sol–gel method, Dy0.75Fe1.25
O
3
orthoferrite
nanoparticles can be synthesized at a relatively low temperature.
When the calcination temperature is lower, soft magnetic phase
will coexist in the samples. The results show that orthoferrite
phase is completely recovered when the calcination temperature
T (1C)
d
(mm/s)
E
Q
(mm/s)
H
hf (KOe)
RA (%)
6
00
00
0.33
1.06
–
35.2
15.8
49.0
3
+
0
.25
.37
0
477
508
is about 700 1C. Although excessive Fe ions were introduced,
0
ꢁ0.11
3+
none of these iron spins couple magnetically with Dy ions. The
results can help understand the nature of magnetic interactions in
structures of this type and the applications of rare-earth
orthoferrites.
7
0.36
.38
0.02
501
517
56.8
43.2
0
ꢁ0.22
Q
d, isomer shift relative to a-Fe; E , quadrupole shift; Hhf, hyperfine field; RA,
relative spectra area.
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samples measured at room temperature. The black dots represent
the experimental data. The lines through the data points are the
results of the least-squares fit to the experimental data and the
other lines above the data are the lines of individual components.
The lines with central doublet indicate the paramagnetic phase
while the other sextets mean different magnetic phase. The
M o¨ ssbauer parameters of different samples are listed in Table 1.
Fig. 5(a) presents a central doublet and sextets, which means
the existence of paramagnetic phase in the samples calcined at
[
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(
(
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M o¨ ssbauer spectra are consistent with that magnetization
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[
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3
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