Full text of DOI:10.1557/JMR.2000.0052

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Preparation and magnetic properties of nanosized amorphous
ternary Fe–Ni–Co alloy powders
Kurikka V.P.M. Shafi and Aharon Gedankena)
Department of Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel
Ruslan Prozorov
Department of Physics, Bar-Ilan University, Ramat-Gan 52900, Israel
Adam Revesz and Janos Lendvai
Department of General Physics, Lorand Eotvos University, H-1088, Budapest, Hungary
(Received 1 August 1999; accepted 29 October 1999)
Nanosized amorphous alloy powders of Fe25Ni13Co62, Fe38Ni23Co39, Fe40,Ni24,Co36,
and Fe69Ni9Co22 were prepared by sonochemical decomposition of solutions of volatile
organic precursors, Fe(CO)5, Ni(CO)4, and Co(NO)(CO)3 in decalin, under an argon
pressure of 100 to 150 kPa at 273 K. The amorphous nature of these particles was
confirmed by various techniques, such as scanning electron microscopy, transmission
electron microscopy, electron microdiffraction, and x-ray diffractograms. Magnetic
measurements indicated that the as-prepared amorphous Fe–Ni–Co alloy particles were
superparamagnetic. The observed magnetization measured up to a field of 1.5 kG of
the annealed Fe–Ni–Co samples (75–87 emu g−1) was significantly lower than that for
the reported multidomain bulk particles (175 emu g−1), reflecting the ultrafine nature
of our sample.
I. INTRODUCTION
the melting point, thus making it possible to quench the
alloy through its glass temperature rapidly enough to
form the amorphous phase. Although these metalloids
stabilize the amorphous phase, their presence drastically
alters the magnetic properties of the alloys. The electron
donated to the d band changes the electronic environment
and thus lowers the saturation magnetization (Ms) and
Curie temperature (Tc).5
Soft magnetic alloys with high-saturation magnetiza-
tion, reduced magnetocrystalline anisotropy, and zero
magnetostriction, are the technologically important
magnetic materials.7,8 An Fe–Ni–Co alloy system is
particularly interesting as many compositions with zero
magnetostriction are known in this system. The Perm and
the Super Invar properties of some of the Fe–Ni–Co al-
loys, coupled with the dependence of magnetic and me-
chanical properties on the ␣ ↔ ␥ martenistic structural
transformations of it, make this system a versatile one for
technological applications.9,10
To our knowledge, no amorphous Fe–Ni–Co ternary
alloy system without any glass former (metalloid), has
been reported so far in the literature. Recently, Ishio
et al.11 have studied the magnetostrictive properties of
CoxFeyNiz alloy system (0.9 ജ x ജ 0.4, 0.5 ജ y ജ 0.15,
and 0.4 ജ z) in the composition region of the face-
centered-cubic (␥) phase. Magnetostriction and magneto-
resistance in the Fe–Ni–Co ternary alloy system have
also been examined by Miyazaki et al.12,13 Magnetic
Amorphous alloys—metallic glasses or glassy metals
obtained by rapid quenching of the melt—lack the long-
range atomic order of their crystalline counterparts. The
unique electronic, magnetic, and corrosion-resistant
properties,1–4 make these systems technologically impor-
tant. For example, the ferromagnetic amorphous alloys
containing Fe and Co have excellent soft magnetic prop-
erties equivalent or superior to those of conventional ma-
terials and are being used in magnetic storage media and
power transformer cores.5 The high resistivity of the
amorphous alloys, generally 2 to 4 times larger than the
corresponding transition metal crystalline alloys, results
in a smaller eddy current contribution to the permeability
and losses, which is very important at higher frequency
device applications.6
Transition metal alloys with a wide variety of metal-
loids, such as transition metal–metalloid alloys (TM-M)
and rare earth–transition metal (RE-TM) alloys, have
been reported, the TM-M alloys typically contain about
80 at.% Fe, Co, Ni with the remainder being B, C, Si, P,
or Al as glass formers. The use of glass former is to lower
a)Address all correspondence to this author.
e-mail: gedanken@mail.biu.ac.il
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K.V.P.M. Shafi et al.: Preparation and magnetic properties of nanosized amorphous ternary Fe–Ni–Co alloy powders
properties and the ␣ ↔ ␥ martenistic structural transfor-
mations have been investigated by Achilleos et al.14 and
others.15
Because the atomic numbers of Fe, Ni, and Co are close
to each other, the alloy composition was estimated from
the ratio of the x-ray emission intensities from these el-
ements. The x-ray intensity was not corrected for absorp-
tion and fluorescence effects as these particles were
much smaller than the free path for x-ray transmission
through solids (i.e., 100 nm).
The elemental analyses of the as-prepared samples
show that the amorphous alloy powders have over 95%
metal by mass, with small amounts of carbon (<3%) and
oxygen (<2%). The presence of carbon and oxygen is
presumably a result of the decomposition of alkane sol-
vents during ultrasonication or adsorbed CO. The infra-
red spectra of the as-prepared samples showed peaks at
2100 cm−1 characteristic of adsorbed CO molecules on
the surface. These impurities probably play an important
role in stabilizing the amorphous structure of the sam-
ples.21 Further the analyses of the annealed samples
(heated at 300 °C under high pure Ar for 10 h) showed
only <0.5% of C, H, and O, and this indicated that
the adsorbed surface impurities were almost completely
removed.
The chemical effect of ultrasound does not originate
from a direct coupling with molecular vibrations but
from a nonlinear phenomenon called cavitation, which
involves the formation, growth, and subsequent implo-
sive collapse of a bubble in a liquid. Acoustic cavitation
generates a transient localized hot spot with an effective
temperature of 5000 K and a submicrosecond collapse
time.16–18 The rapid cavitational cooling rate (>109 K s−1)
is much higher than that obtained by the conventional
melt-spinning19 (105 to 106 K s−1) technique used to
prepare amorphous materials. We have explored
this cavitation phenomenon to prepare the amorphous
metals,20 alloys,21,22 oxides,23 and ferrites.24,25 Here we
discuss the sonochemical synthesis and characterization
of nanosized amorphous Fe–Ni–Co particles. This is a
continuation of our work on the bimetallic metal alloys
Co–Ni reported earlier in this journal.22
II. EXPERIMENTAL
The Fe–Ni–Co alloy was prepared by our previously
published method for Co–Ni alloys22 by ultrasonic irra-
diation of the solution of Fe(CO)5, Co(NO)(CO)3 and
Ni(CO)4 in decane at 273 K under 100 to 150 kPa (1 to
1.5 atm) of argon, with a high-intensity ultrasonic probe
(Sonics and Materials, model VC-600) (1.25-cm Ti horn,
20 kHz, 100 W cm−2). The various compositions of Fe–
Ni–Co (Fe25Ni13Co62, Fe38Ni23Co39, Fe40Ni24Co36,
Fe69Ni9Co22) were prepared by varying the molar con-
centration of the precursors in solution.
Powder x-ray diffractograms were recorded on a
Rigaku x-ray diffractometer (Cu K␣ radiation, ␭ ס
0.15418 nm). Scanning electron micrographs and energy
dispersive x-ray analysis (EDX) were carried out on a
JEOL-JSM-840 electron microscope. Transmission
electron micrographs were obtained with a JEOL-
JEM100SX electron microscope. Magnetization loops
were measured at room temperature with an Oxford In-
strument vibrating sample magnetometer. Surface area
[Brunauer–Emmett–Teller (BET) method] was measured
on a Micromeritics-Gemini surface area analyzer. Differ-
ential scanning calorimetry (DSC) thermograms were
obtained on a Mettler-Toledo DSC 25 calorimeter at a
heating rate of 10 °C/min under flowing pure argon
(50 ml/min). Elemental analyses were carried out on an
EA 1110 CHNS-O analyzer. All sample preparation
and transfer for these measurements were done inside a
glove box.
Electron microdiffraction and x-ray diffraction tech-
niques confirm the amorphous nature of the alloy par-
ticles. The transmission electron microscope (TEM)
image (Fig. 2) of the as-prepared Fe38Ni23Co39 sample
shows the alloy powders as agglomerates of small par-
ticles with overall diameters of <10 nm. The exact size of
the particle is difficult to determine as most of the par-
ticles are aggregated in a spongelike form. The TEM
microdiffraction [Fig. 2(a) inset] of the alloy particles
shows only diffuse rings characteristic of amorphous
materials. The other as-prepared samples behave in a
similar fashion. The TEM micrograph of the annealed
Fe38Ni23Co39 sample (heated at 500 °C for 5 h under Ar)
is shown in Fig. 3. Uniform near-spherical particles of
<10 nm can be seen in this micrograph. The x-ray dif-
fraction pattern for the as-prepared sample as well as
the annealed samples of Fe25Ni13Co62 and Fe69Ni9Co22
III. RESULTS AND DISCUSSION
Alloy compositions were determined by elemental and
energy-dispersive x-ray analyses. The EDX profile of a
representative sample, Fe69Ni9Co22, is shown in Fig. 1.
FIG. 1. EDX profiles for annealed Fe69Ni9Co22 alloy sample.
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K.V.P.M. Shafi et al.: Preparation and magnetic properties of nanosized amorphous ternary Fe–Ni–Co alloy powders
FIG. 2. TEM image of amorphous Fe38Ni23Co39 with microdiffrac-
FIG. 3. TEM image of annealed Fe38Ni23Co39 alloy sample.
tion patterns (inset).
(heat treated under pure argon at 500 °C for 5 h) are
shown in Fig. 4. The as-prepared amorphous sample
[Fig. 4(a)] shows no sharp diffraction pattern indicating
the amorphous nature. The pattern for the Fe69Ni9Co22
sample shows peaks characteristic of the ␣-phase as well
as the ␥-phase, while the pattern for Fe25Ni13Co62 shows
peaks predominantly of the ␥-phase. The ␥-phase is of
the Fe–Ni type in the disordered state and the ␣-phase is
that of the Fe–Co alloy system. The existence of both ␣-
and ␥-phases in the annealed samples is due to the ␣ ↔
␥ martenistic structural transformations. The alloy sys-
tems Fe38Ni23Co39, Fe25Ni13Co62, and Fe40Ni24Co36 lie
at the boundary of the ␣- and the ␥-phase, while the
system Fe69Ni9Co22 is in the ␣-region of the phase dia-
gram of the ternary Fe–Ni–Co system.12 The magnetiza-
tion curve of the amorphous sample Fe69Ni9Co22
measured at room temperature (Fig. 5) does not reach
saturation even at a magnetic field of 15 kG, and no
hysteresis is found, indicating that the as-prepared (amor-
phous) Fe–Ni–Co particles are superparamagnetic. Other
samples behave similarly. Figure 6 shows the magneti-
zation curves of the annealed samples of Fe–Ni–Co al-
loys. (The scale in Fig. 6 is larger than that in Fig. 5
because of the crystalline nature of the compound.) The
magnetic properties of the various compositions of the
alloy particles are given in Table I. The observed values
of magnetization of the annealed samples, 77–87 emu g−1
at high enough field of 15 kG, are significantly lower
than that for the reported15 multidomain Fe–Ni–Co par-
ticles (175–180 emu g−1), and this reflects the ultrafine
nature of our sample. Specifically, the difference in the
magnetization value between the bulk and our nanosized
materials can be attributed to the small particle size ef-
fect. This can be readily seen from the high surface area
of our annealed samples (i.e., 25–35 m2/g) and the small
particle sizes (10–15 nm) estimated from broadening of
x-ray lines with the Scherrer equation (see Table I). The
decrease in surface area of the heated sample is due to the
increase in particle size by sintering. It is known that the
magnetic properties, like saturation magnetization and
hyperfine field value, of nanoparticles are much smaller
than those of the corresponding bulk materials.22,24–28
Because the energy of a magnetic particle in an external
field is proportional to its volume (via the number of
magnetic molecules), it decreases as the cube of the lin-
ear particle dimension. When this energy becomes com-
parable to kT, thermal fluctuations will significantly
reduce the total magnetic moment at a given field. The
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K.V.P.M. Shafi et al.: Preparation and magnetic properties of nanosized amorphous ternary Fe–Ni–Co alloy powders
large surface-to-volume ratio for small particles can also
lead to decreased magnetization values. The magnetic
molecules on the surface lack complete coordination. Fi-
nally, antiferromagnetic impurities like oxide and carbide
can also decrease the total magnetization. Adsorbed car-
bonyl on amorphous materials can lead to metal carbide
or oxide during sonication or the heating process.29
The DSC curves of the as-prepared amorphous Fe–
Ni–Co samples are shown in Fig. 7. Wide endothermic
peaks below 300 °C in all the samples are due to desorp-
tion of adsorbed carbonyl and hydrocarbon solvent im-
purities. These peaks vanish in the successive runs of the
DSC and this indicates the desorption endotherms of
the adsorbed surface impurities. The crystallization be-
havior of the samples are different. The Fe69Ni9Co22
sample [Fig. 7(a)] shows a wide exothermic peak cen-
tered around 310 °C. In the Fe40Ni24Co36 sample [Fig.
7(b)] two exothermic peaks are detected, one at 370 and
another at 400 °C, respectively. However, in the
Fe25Ni13Co62 sample [Fig. 7(c)], the sharp exothermic
peak is at 370 °C and is immediately followed by another
sharp endotherm at 390 °C. The crystallization peak of
the Fe38Ni23Co39 sample [Fig. 7(d)] is a sharp one at
365 °C and no endotherm is detected afterward. These
exo- and endothermic peaks completely vanish in the
successive run, showing the irreversible nature of the
transition. Further, we have examined the DSC curve of
Fe25Ni13Co62 sample, after annealing at 300 °C for 5 h to
remove completely the surface adsorbed impurities, to
check the possible role of the contaminants on the endo-
therm at 390 °C. The endothermic peak is still seen on
the DSC curve even though shifted to 400 °C. From these
FIG. 5. Room-temperature magnetization curves of amorphous
Fe69Ni9Co22 sample.
FIG. 6. Room-temperature magnetization curves of annealed Fe–Ni–
Co samples: (a) Fe38Ni23Co39, (b) Fe25Ni13Co62, (c) Fe69Ni9Co22, and
FIG. 4. XRD patterns for (a) amorphous Fe25Ni13Co62, (b) annealed
Fe69Ni9Co22 sample, and (c) annealed Fe25Ni13Co62 sample.
(d) Fe40Ni24Co36
.
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K.V.P.M. Shafi et al.: Preparation and magnetic properties of nanosized amorphous ternary Fe–Ni–Co alloy powders
TABLE I. Compositions and magnetic properties of annealed alloy samples.
Surface
Fe
(at.%)
Ni
(at.%)
Co
(at.%)
Pseudobinary
type
Ms
(emu/g)
Mr
(emu/g)
Hc
(G)
area
Size
(nm)
(m2/g)
1
2
3
4
24.75
37.82
40.22
69.15
13.16
22.73
23.65
9.16
62.09
39.45
36.13
21.69
(Fe0.65Ni0.35 38
(Fe0.62Ni0.38 61
(Fe0.63Ni0.37 64
)
)
)
Co2
Co39
Co36
77.00
87.00
75.00
83.00
31.00
17.00
23.00
14.00
814
230
550
260
33
25
35
28
11.2
15.4
10.5
13.9
Fe69Ni9Co22
FIG. 7. DSC curve of amorphous samples: (a) Fe69Ni9Co22, (b) Fe40Ni24Co36, (c) Fe25Ni13Co62, and (d) Fe38Ni23Co39
.
observations, we believe that the endotherms following
the crystallization exotherms of the Fe–Ni–Co samples
have to do with some kind of magnetic phase transition,
the nature of which is not clear now. Systematic and
detailed studies, like thermomagnetometry (TM) and
variable temperature x-ray diffraction, are required to
study this transition.
ence & Arts for the Binational Indo-Israel Grant as well
as the Hungary–Israel exchange scientist program.
A. Gedanken is grateful to the Bar-Ilan Research Au-
thorities for supporting this project. R. Prozorov ac-
knowledges support from the Clore Foundations. We
thank Prof. M. Deutsch for use of x-ray diffraction fa-
cilities and Prof. Y. Yeshurun for extending the facilities
of the National Center for Magnetic Measurements at the
Department of Physics, Bar-Ilan University.
IV. CONCLUSIONS
Sonochemical decomposition of the solutions of
volatile organic precursors Fe(CO)5, Co(NO)(CO)3, and
Ni(CO)4 in decalin at 273 K, under an argon pressure of
100 to 150 kPa (1 to 1.5 atm), yield amorphous, nano-
sized Fe–Ni–Co alloy particles. The composition of these
alloy particles can be controlled by varying the initial
precursor concentration in solution. Magnetic data indi-
cate the superparamagnetic nature of the as-prepared
amorphous sample and also the ultrafine nature of the
crystallized sample.
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This research was supported by Grant No. 94-00230
from the US–Israel Binational Science Foundation
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