APPLIED PHYSICS LETTERS 86, 162501 共2005兲
Soft magnetic ternary iron-boron-based bulk metallic glasses
Chih-Yuan Lin, Hung-Yu Tien, and Tsung-Shune China兲
Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu, 30043, Taiwan,
Republic of China
共Received 19 August 2004; accepted 16 March 2005; published online 11 April 2005兲
Ternary iron-boron-based bulk metallic glasses 共BMGs兲 were explored exhibiting capability of thick
amorphous casting at least 1 mm in rod diameter or 0.5 mm in plate thickness, excellent soft
magnetic properties with saturation magnetization 1.56 T and coercivity smaller than 40 A / m, and
electrical resistivity larger than 200 ␮⍀ cm. The BMG alloys represented by the formulas M aFebBc
are based on two simple selection rules: 共1兲 M is an element with an atomic radius at least 130% that
of Fe; 共2兲 M possesses eutectic points with both Fe and B, and the M-Fe eutectic is at the Fe-rich
end. Among more than 30 candidate M elements, Sc, Y, Dy, Ho, and Er fulfill BMG capability at
the composition range, in at %, 3 ⬍ a ⬍ 10, 18⬍ c ⬍ 27, whereas a + b + c = 100. It is very remarkable
that with a tiny addition of M, such as 4 at %, the critical cooling rate to form an amorphous state
is abruptly lowered by more than four orders of magnitude as compared with Fe-B binary alloys,
and a bulk amorphous state is achievable with only three elements 共conventional ones 4–7
elements兲. These alloys are promising as core materials for transformers. © 2005 American Institute
of Physics. 关DOI: 10.1063/1.1901808兴
Since the preparation of amorphous Fe-P-C thin foils in
1967 by a rapid solidification technique,1 a large number of
iron-based amorphous metals have been subsequently developed. It is well known that such alloys are very attractive
because of their excellent soft magnetic properties. These
materials have been widely used in electrical devices such as
transformer cores.2 If all the core materials of transformers
and motors will be made of iron-based amorphous metals,
the impact on energy saving and reduction in CO2, thus environmental benefits, will be beyond imagination. However,
all the suitable iron-based amorphous metals have a thickness limited to around 30 ␮m due to their poor glass forming
ability 共GFA兲, so that a very rapid cooling is required by
using a rapid solidification method such as a plane-flow casting technique.2 Much research has endeavored to develop
thicker amorphous sheets in order to extend their industrial
applications. Since 1995, a number of Fe-based bulk metallic
glass 共BMG兲 systems have been developed. They consist
mainly of the following groups of elements: Fe-共Al, Ga兲-共P,
C, B, Si兲 共Refs. 3–6兲, Fe-共Co, Ni兲-共Zr, Nb, Hf兲-B 共Refs.
7–9兲, 共Fe, Co兲-共Zr, Hf兲-共Nb, Ta兲-共Mo, W兲-B 共Refs. 10兲,
Fe-M-Si-B 共M = Nb or Zr兲 共Refs. 11 and 12兲, and some
pseudoternary Fe-based bulk metallic glasses such as 共Fe,
Co兲-Ln-B 共Refs. 13–15兲. Quite a number of rules were developed to predict the GFA of an alloy. However, up to now,
no exact theorem has been built. The BMGs developed earlier were based on three empirical rules elucidated by
Inoue:16 共1兲 a multicomponent system containing more than
three elements; 共2兲 a large size difference in atomic radius
among major elements, typically more than 12%; and 共3兲
high negative heat of mixing. Although ternary Nd-Fe-Al
alloys were demonstrated to be good BMGs,17 they are rareearth-based hard magnets with 60– 70 at % Nd, hence low
magnetization. There are indications of simple Fe-R-B ternary alloys exhibiting either a large supercooled liquid re-
gion or good nanocrystallization capability with R being one
of Nb, Zr, and Hf 共Refs. 18–23兲. However, reports of bulk
metallic glasses based on these compositions have not been
available in open literature, including patents. On the other
hand, existing Fe-based multicomponent BMGs exhibit low
saturation magnetization, typically below 1.4 T, due to their
low Fe content and complex composition,3–10,24–26 except
those with only four component elements, 1.5 T 共Refs. 12
and 13兲. In this study, we have unveiled compositional selection rules modified from the above empirical rules to achieve
ternary Fe-based bulk glassy alloys represented by M-Fe-B.
They are based on the enhancement of GFA for Fe-B binary
alloys by using a small amount of the third element. Hence,
the proposed design rules are: 共1兲 M is a much larger atom,
which we set at least 130% the atomic radius of Fe; 共2兲 M
should have eutectic points with both Fe and B 共so that M
has large and negative heat of mixing both with Fe and B兲,
and the M-Fe eutectic shall be at the Fe-rich region, hence
the required M content is the least. With the proposed rules,
we have disclosed several unique ternary Fe-based BMGs
after laborious trials.
Ternary alloy ingots with nominal compositions, including M 6Fe72B22 共M was selected from one of Zr, Hf, Nb, Ta,
Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, U兲
and YaFe共100−a−c兲Bc 共a = 1 – 10 at %, c = 18– 28 at %兲, were
a兲
Author to whom correspondence should be address: present address: National Tsing Hua University, Department of Materials Science and Engineering, 101, Sec. 2. Kuang-Fu Road, Hsinchu, 30043, Taiwan, Republic
of China; electronic mail: [email protected]
FIG. 1. X-ray diffractograms taken on cross sections of as-cast rods 1 and
2 mm in diameter of an Y6Fe72B22 alloy, Cu K␣1.
0003-6951/2005/86共16兲/162501/3/$22.50
86, 162501-1
© 2005 American Institute of Physics
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162501-2
Appl. Phys. Lett. 86, 162501 共2005兲
Lin, Chin, and Tien
TABLE I. The ability to form bulk glassy rods of at least 1-mm-diam for the studied M 6Fe72B22 alloys.
M
Zr
Hf
Nb
Ta
Sc
Y
La→ Tb
Dy
Ho
Er
BMG or not
no
no
no
no
yes
yes
no
yes
yes
yes
prepared by arc melting in a copper crucible mixtures of
prealloyed Fe-B ingots, beads of pure M metal of at least
99.5% purity, under a vacuum 0.01 MPa. Glassy ribbons
with a cross section of about 0.03⫻ 3 mm2 were prepared by
a single-roller melt-spinning technique. Rods or plates with
different diameters or thicknesses were prepared by injection
casting into a copper mold. The structure of ribbons and
as-cast rods/plates was examined by x-ray diffractometry
共XRD兲. Thermal stability was studied by differential scanning calorimetry 共DSC兲 at a heating rate of 20 K / min. Magnetic properties, including saturation magnetization 共Is兲 and
coercive force 共Hc兲, were measured with a vibrating sample
magnetometer 共VSM兲. Curie temperature 共Tc兲 was measured
by a thermal-gravimetric analyzer under a magnetic field of
0.02 T 共M-TGA兲 at a heating rate of 5 K / min.
First of all, the elements selected using the above two
rules were examined. Table I summarizes the as-cast results
of some of the selected elements. We can see that scandium
共Sc兲, yttrium 共Y兲, dysprosium 共Dy兲, holmium 共Ho兲, and erbium 共Er兲 exhibited good glass forming ability in forming
glassy rods of at least 1 mm in diameter, or plates at least
0.5-mm thick. According to the results, one can see that the
alloys with M being one of zirconium, hafnium, niobium, or
tantalum, whose atomic size is smaller than 130% that of Fe,
failed to form BMG, though they possess eutectic points
with Fe and B. Those elements possessing no Fe-rich eutectic point with Fe, such as lanthanum, cerium, praseodymium,
neodymium, samarium, gadolinium, and terbium, also failed
to form BMGs, even though they have an atomic size much
larger than 130% that of Fe. Only elements such as Sc, Y,
Dy, Ho, and Er that simultaneously satisfy our two proposed
rules, exhibited good GFA to form ternary bulk metallic
glasses. The experimental results prove the validity of our
proposal for the selection of simple ternary Fe-based bulk
glassy alloys.
Second of all, further GFA tests showed that the alloys
Sc6Fe72B22, Y6Fe72B22, and Er6Fe72B22 exhibit excellent
GFA to form glassy rods with a diameter of at least 2 mm.
Figure 1 depicts the x-ray diffraction patterns taken from the
transverse cross sections of as-cast rods of Y6Fe72B22 with 1
and 2 mm diam, respectively, showing an amorphous structure. DSC studies revealed that the Sc-added alloy possessed
much lower Tg and Tx than others. The ⌬Tx 共Tx − Tg兲 became
the largest 共42 K兲 as M is yttrium, and the smallest 共16 K兲 as
M is erbium.
We then varied the amount of yttrium addition to test the
composition range for BMGs. Figure 2 shows the composition region for the formation of at least 1-mm diam bulk
glassy rod in the Fe-Y-B ternary alloy. For corresponding
plate casting, the achievable thickness is 0.5 mm. It shows a
very wide bulk glassy formation range as 3 ⬍ Y ⬍ 10 at %
and 18⬍ B ⬍ 27 at %. Other systems of Fe-M-B alloys 共M
= Sc, Dy, Ho, Er兲 兲 also exhibited a similar, wide BMG forming region around the composition of M 6Fe72B22. For example, 2-mm glassy rods were successfully achieved in
Sc6Fe72B22, Y6Fe72B22, and Er6Fe72B22.
It is well known that the binary Fe-B system exhibit poor
glass forming ability to form a glassy ribbon around 30 ␮m
in thickness only by a rapid solidification technique, such as
melt spinning, corresponding to a cooling rate of 106 K / s. It
was indeed very astonishing that with a tiny amount of M
addition, such as 4 – 6 at % Sc, Y, Dy, Ho, and Er, the critical
cooling rate 共Rc兲 to form an amorphous state is at least four
orders of magnitude lower. A bulk glassy state is possible
through an injection casting into a copper mold that has a
cooling rate only of 10– 102 K / s. On the other hand, it has
long been recognized that Fe-based BMGs are quite difficult
to achieve through simple compositions. They were known
to be achievable for alloys with more than three elements,
and in practice only for alloys containing 4–7 elements.13–15
We believe that the proper packing of an extremely large
atom 共such as Sc, or Y兲 with its eutectic 共negative-heat-ofmixing兲 and medium-sized counterpart, iron, and the extremely small atom, boron, has led to a topological effect that
hinders one another from crystallization. This will then open
a door to attain simple BMGs other than Fe-based alloys.
FIG. 2. The composition range for the formation of bulk glassy metals, with
FIG. 3. The saturation magnetization 共Is兲 of YaFe78−aB22, a = 4 – 9 at %, and
at least 1-mm-diam, in the Y-Fe-B ternary system.
M 6Fe72B22 bulk metallic glasses, with M being one of Sc, Y, Dy, Ho, and Er.
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162501-3
Appl. Phys. Lett. 86, 162501 共2005兲
Lin, Chin, and Tien
TABLE II. A comparison of saturation magnetization 共Is兲 for various Febased BMGs.
BMG alloy systems
Is
共T兲
This study
Y4Fe76B20
M 6Fe72B22 共M = Sc/ Dy/ Ho/ Er兲
1.56
1.2–1.3
Fe-B-Si ribbon
Fe80B11Si9a
1.59
Known Fe-based BMGs
共Fe,Co,Ni兲-共Zr,Nb,Hf兲-Bb
Fe-Al-Ga-共P,Si,B兲c
Fe-Co-Ln-Bd
Fe-Nb-Si-Be; Fe-Zr-Si-Bf
1.0
1.3
1.37
⬎1.5
a
Reference 2.
Reference 7–9.
c
Reference 3–6.
d
Reference 14.
e
Reference 12.
f
Reference 13.
b
The Curie temperature 共Tc兲, measured by a thermogravimetry analyzer coupled with a magnetic field
共M-TGA兲, decreases from 568 to 487 K as Y and B increases from 4 to 8 and 22 to 26 at %, respectively. Figure 3
shows the variation in saturation magnetization 共Is兲 of the
M-Fe-B bulk glassy alloys. The results show that the
YaFe78−aB22 BMGs exhibit much higher Is than other
M aFe78−aB22 ternary BMGs under study, and attain the highest Is at the Y content of 4 – 6 at %, up to 1.52 T. For a BMG
of Y4Fe76B20 an Is of 1.56 T was attained, which is higher
than those of reported multicomponent Fe-based BMGs and
comparable with Fe80B11Si9 amorphous ribbon, as can be
seen in Table II. Yttrium has no magnetic moment at all, so
that it plays a simple role of diluting the magnetic moment,
whereas Dy, Ho, and Er are heavy rare earths that are antiferromagnetically coupled with Fe so that the saturation
magnetization is greatly reduced. Sc was also found to be
antiferromagnetically coupled with Fe in Fe-Sc binary amorphous alloys.27 We propose that Sc behaves the same way in
our amorphous ternary Sc-Fe-B alloys resulting in a lowered
saturation magnetization. The coercive force 共Hc兲 of all the
as-cast ternary BMGs was smaller than 40 A / m, with the
smallest being 4 A / m for Y6Fe72B22. The electrical resistivity of the M-Fe-B glassy alloys measured by a four-pointprobe method from melt-spun ribbons for each composition
is typically 200– 290 ␮⍀ cm and increasing with M and B
contents. This is almost two times that of the conventional
amorphous Fe78Si9B13 ribbon 共around 140 ␮⍀ cm兲 and five
times that of silicon steels 共around 50 ␮⍀ cm兲. The reason is
very simple that the extremely large difference in atomic size
among M, Fe, and B induces, at the atomic scale, enormous
lattice strain that contributes to extra electronic scattering
during electrical transport.
In summary, simple rules of composition selection for
Fe-B-based ternary bulk glassy alloys, M-Fe-B, were established by modifying the previous empirical rules: 共1兲 M is an
element with an atomic radius at least 130% that of Fe; 共2兲
M possesses eutectic points with both Fe and B, and the M
-Fe eutectic is at the Fe-rich end. This led to an excellent
outcome, whereby the addition of a tiny amount of M, such
as 4–6%, with M being one of Sc, Y, Dy, Ho, or Er, the
critical cooling rate to form an amorphous state is abruptly
lowered by more than four orders of magnitude as compared
with the Fe-B binary alloys. It is also surprising that for a
long time, Fe-based BMGs were recognized to be achievable
for alloys containing more than three elements, and in practice 4–7 elements. The ternary BMGs thus developed are
characteristic of high saturation magnetization 1.2– 1.56 T,
low coercivity less than 40 A / m, and high electrical resistivity, larger than 200 ␮⍀ cm. Among the explored ternary
BMGs, Y-Fe-B alloys show the highest saturation magnetization, 1.56 T, and display great potential for application due
to the cheap and relatively abundant yttrium, besides their
promising magnetic properties. Also, the magnetic interaction between Sc, Y, Dy, Ho, Er, and the amorphous Fe-B
matrix is worthy of further investigation.
The authors are grateful to the National Science Council
of the Republic of China for sponsoring this research under
Grants No. NSC90-2216-E007-062, NSC91-2120-M007001, and NSC92-2120-M007-006.
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