DSpace at VNU: Magnetic Properties of FePd Nanoparticles Prepared by Sonoelectrodeposition

Journal of ELECTRONIC MATERIALS

DOI: 10.1007/s11664-016-4565-7
Ó 2016 The Minerals, Metals & Materials Society

Magnetic Properties of FePd Nanoparticles Prepared
by Sonoelectrodeposition
NGUYEN HOANG LUONG,1,3 TRUONG THANH TRUNG,1
TRAN PHUONG LOAN,1 LUU MANH KIEN,2 TRAN THI HONG,1
and NGUYEN HOANG NAM1
1.—Hanoi University of Science, Vietnam National University, Hanoi, 334 Nguyen Trai Road,
Hanoi, Vietnam. 2.—Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043,
Japan. 3.—e-mail:

Fe60Pd40 nanoparticles were prepared by sonoelectrodeposition. After
annealing at various temperatures from 450°C to 700°C, the nanoparticles
were found to have an ordered L10 structure and to show hard magnetic
properties. Among the samples investigated, the nanoparticles annealed at
600°C exhibited the highest coercivity which amounts to 2.31 kOe at 2 K and
1.83 kOe at 300 K.
Key words: FePd, L10 structure, sonoelectrodeposition, magnetic
nanoparticles, hard magnetic materials

INTRODUCTION
FePd nanoparticles have attracted interest for
their potential applications in ultrahigh-density
magnetic recording media due to the large uniaxial
magnetocrystalline anisotropy of Ku $ 1.8 9 107
erg cmÀ3 of the L10 ordered structure.1–11 Ordered
face-centered tetragonal (fct) L10 FePd materials
are normally obtained from disordered face-centered cubic (fcc) materials via the order–disorder

transition. Several approaches to the preparation of
FePd nanoparticles have been reported including
epitaxial growth by electron beam deposition,4–6
chemical synthesis7,8,11 (which is modified from the
FePt nanoparticles synthesis method by Sun
et al.12), modified polyol process,9 and microwave
irradiation2. As pointed out by Watanabe et al.,9
FePd nanoparticles synthesized by the modified
polyol process including thermal decomposition do
not exclusively show the ordered L10 phase transition similar to L10-type materials such as FePt and
CoPt. Especially, the FePd nanoparticles prepared
by Chen and Nikles11 did not transform to the L10
phase after annealing at a sufficiently high temperature of 700°C.

(Received October 12, 2015; accepted April 21, 2016)

We have previously reported the hard magnetic
properties of FePd nanoparticles synthesized by
sonochemistry.13 In this paper, we report the use of
the sonoelectrodeposition method for the preparation of FePd nanoparticles. To our knowledge, FePd
nanoparticles have never been fabricated by sonoelectrodeposition, which is a technique combining
the advantages of electrodeposition and the
mechanical waves of ultrasound to produce metallic
nanoparticles.14 Recently, Co–Pt nanoparticles
encapsulated in carbon cages prepared by sonoelectrodeposition have been reported by Luong et al.15
Magnetic properties of FePt nanoparticles also
prepared by sonoelectrodeposition have been
reported by Nam et al.16
EXPERIMENTAL
The experimental setup employed by us is similar

to that described in Ref. 17 A titanium horn of
diameter of 1.3 cm acted as both the cathode and
ultrasound emitter (Sonics VCX 750). The electroactive part of the sonoelectrode was the planar
circular surface at the bottom of the Ti horn, while
an isolating plastic jacket covered the immersed
cylindrical part. This sonoelectrode produced a sonic
pulse that immediately followed a current pulse. A
home-made galvanostat was used to control the
constant current regime (without using a reference


Luong, Trung, Loan, Kien, Hong, and Nam

Fig. 1. TEM image and size distribution of the as-prepared Fe60Pd40 nanoparticles.

Fig. 2. TEM image and size distribution of the annealed Fe60Pd40 nanoparticles (600°C/1 h).

electrode). A platinum plate of 1 cm2 was used as a
counter electrode. The density of the current pulse
was 15 mA/cm2. The duration, ton, of the current
pulse was 0.5 s, then the current was turned off for
a duration, toff, of 0.8 s. During ton, FePd nanoparticles were deposited on the surface of the electrode.
When the current was switched off, a 0.2-s ultrasound pulse of power density 100 W/cm2 was activated to remove the nanoparticles from the
electrode.
The volume of the electrolysis cell was 100 ml
containing 0.15 M iron(II) acetate [Fe(C2H3O2)2],
0.1 M palladium(II) acetate [Pd(C2H3O2)2], and
0.5 M Na2SO4, which were mixed under
(Ar + 5%H2) atmosphere. After deposition, the FePd
nanoparticles were washed and separated from the

solution by using a centrifuge (Hettich Universal
320) at 5000 rpm for 30 min. Nanoparticles were
dried in air at 70°C for 30 min. The as-prepared
samples were then annealed at various temperatures from 450°C to 700°C for 1 h under
(Ar + 5%H2) atmosphere. The structure of the

nanoparticles was characterized by an x-ray diffractometer (XRD; D5005, Bruker). The average crystallite size, d, was calculated from the line
broadening using Scherrer’s formula, d = 0.9k/
(Bcosh), where k is the wavelength of x-rays and B
is the half-maximum line width. The particle morphology was examined by a transmission electron
microscope (TEM; JEM1010, JEOL). The chemical
composition of our sample was Fe60Pd40 as revealed
from energy dispersion spectroscopy (EDS;
OXFORD-ISIS 300) measurements. Magnetic properties of samples were studied by using Quantum
Design’s superconducting quantum interference
device (SQUID) with a magnetic field up to 50 kOe
in the temperature range from 2 K to 300 K.
RESULTS AND DISCUSSION
Figures 1 and 2 show the TEM images and size
distributions of the as-prepared and Fe60Pd40
nanoparticles annealed at 600°C, respectively. Particle size of the as-prepared Fe60Pd40 sample was


Magnetic Properties of FePd Nanoparticles Prepared by Sonoelectrodeposition

Fig. 3. XRD patterns of the as-prepared and annealed Fe60Pd40 nanoparticles (600°C/1 h).

about 7–10 nm. After annealing, the particle size
increased to about 15–20 nm, showing that the
particles were agglomerated.

The XRD patterns of the as-prepared and
Fe60Pd40 nanoparticles annealed at 600°C are
shown in Fig. 3. Before annealing, the XRD results
showed the reflections of a pure Pd structure, as
observed in Ref. 13 in FePd nanoparticles prepared
by sonochemistry. The reflections from Fe are very
weak due to the fact that their atomic weight is
much less than that of Pd, which is similar to the
XRD result of FePt foils prepared by cold deformation18 and of FePt nanoparticles prepared by sonoelectrodeposition.16 The average crystallite size
calculated by using Scherrer’s formula was found
to be 10 nm, in agreement with the particle size
obtained from the TEM image. Upon annealing, the
formation of the ordered L10 fct phase occurred.
Samples showed the tetragonal order phase of FePd
alloy with diffraction peaks at 24°, 33°, 41°, 47°, 49°,
53.5°, 60.5°, 69° which can be assigned to (001),
(110), (111), (200), (002), (201), (112), (220) reflections, respectively. The diffraction peak at 44.5° can
be due to the formation of the a-Fe phase in the
sample. By using Scherrer’s formula, the average
crystallite size was estimated to be 20.1 nm for the
sample annealed at 600°C, in agreement with that
obtained from the TEM image.
Magnetic measurements of the as-prepared sample (data not shown) exhibited low saturation
magnetization, MS, and coercivity, HC. After
annealing, the hard magnetic FePd phase was
formed. Figure 4 presents the magnetic curves of
the Fe60Pd40 nanoparticles annealed at 600°C for
1 h at different temperatures. The curves show
typical hard magnetic hysteresis loops, indicating
the effect of annealing. The temperature dependence of the coercivity of Fe60Pd40 nanoparticles

annealed at various temperatures from 450°C to
700°C is shown in Fig. 5, from which it can be

Fig. 4. Magnetic curves of Fe60Pd40 nanoparticles annealed at
600°C for 1 h at different temperatures.

clearly seen that the Fe60Pd40 nanoparticles
annealed at 600°C exhibit the highest coercivity.
For this sample, the coercivity was 2.31 kOe at 2 K
and slightly decreases with increasing temperature
to the value of 1.83 kOe at 300 K. Watanabe et al.9
prepared Fe49.2Pd50.8 nanoparticles by the modified
polyol process, i.e. simultaneous reduction of palladium acetylacetonate (Pd(acac)2) and thermal
decomposition of iron pentacarbonyl (Fe(CO5)) in a
solvent. These authors reported the value of 2.04
kOe at 5 K for the coercivity of Fe49.2Pd50.8 samples
annealed at 600°C for 1 h. We note that the
Fe49.2Pd50.8 nanoparticles in Ref. 9 have been
annealed at only one temperature (600°C). Gajbhiye
et al.19 also prepared Fe43Pd57 nanoparticles by the


Luong, Trung, Loan, Kien, Hong, and Nam

Figure 6 shows the annealing-temperature
dependence of the coercivity of Fe60Pd40 nanoparticles measured at different temperatures. As can be
seen from this figure, the coercivity of the Fe60Pd40
nanoparticles increases with the annealing temperature up to 600°C due to a better atomic ordering of
the fct phase. Further increase of the annealing
temperature decreases the coercivity, suggesting

that a soft phase Fe3Pd exists in the sample, as
supported by our XRD results for the samples
annealed at 650°C and 700°C (data not shown).
CONCLUSIONS

Fig. 5. The temperature dependence of the coercivity of Fe60Pd40
nanoparticles annealed at different temperatures.

Fe60Pd40 nanoparticles have been prepared by
sonoelectrodeposition. After annealing at various
temperatures from 450°C to 700°C, the nanoparticles were found to have an ordered L10 phase, with
good coercivity up to 2.31 kOe at 2 K and 1.83 kOe
at room temperature. Sonoelectrodeposition is a
promising method to make FePd magnetic
nanoparticles.
ACKNOWLEDGEMENTS
This research is funded by Vietnam National
Foundation for Science and Technology Development (NAFOSTED) under Grant Number ‘‘103.022013.61’’. The authors would like to thank Prof. Y.
Nozue of Osaka University, Japan, for providing
SQUID.
REFERENCES

Fig. 6. The annealing-temperature dependence of coercivity of
Fe60Pd40 nanoparticles measured at different temperatures.

modified polyol process and annealed the samples at
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increase of the annealing temperature decreases the
coercivity, suggesting the formation of a new soft
phase Fe3Pd at higher temperature.

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