DSpace at VNU: Annealing effect on soft magnetic properties and magnetoimpedance of Finemet Fe(73.5)Si(13.5)B(9)Nb(3)Au(1) alloy

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Journal of Magnetism and Magnetic Materials 304 (2006) e195–e197
www.elsevier.com/locate/jmmm

Annealing effect on soft magnetic properties and magnetoimpedance
of Finemet Fe73.5Si13.5B9Nb3Au1 alloy
N.D. Thoa, N. Chaua, S.C. Yub,Ã, H.B. Leec, N.D. Thea, L.A. Tuanc
a

Center for Materials Science, Vietnam National University, 334 NguyenTrai, Hanoi, Vietnam
b
Department of Physics, Chungbuk National University, Cheongju 361-763, South Korea
c
Departement of Physics, Kongju National University, Kongju 314-701, South Korea
Available online 3 March 2006

Abstract
Effect of annealing on the soft magnetic properties of Fe73.5Si13.5B9Nb3Au1 amorphous ribbon has been investigated by means of
structure examination, magnetoimpedance ratio (MIR) and incremental permeability ratio (PR) spectra measured in the frequency range
of 1–10 MHz at a fixed current of 10 mA X-ray diffraction analysis showed that the as-cast sample was amorphous and it became
nanocrystalline under a proper heat treatment. When annealing amorphous alloy at 530 1C for 30, 60, 90 min, soft magnetic properties
have been improved drastically. Among the samples investigated, the sample annealed at 530 1C for 90 min showed the softest magnetic
behavior. The MIR and PR curves revealed the desirable changes in anisotropy field depending upon annealing.
r 2006 Elsevier B.V. All rights reserved.
PACS: 75.50.Tt; 73.63.Bd
Keywords: Amorphous magnetic meterials; Nanocrystalline materials; Magnetoimpedance; Permeability

The investigation of ultra soft magnetic materials has
been extensively carried out in the recent years. Their
extremely soft magnetic behaviors achieved upon suitable partial nanocrystallization by heat treatment.

Magnetic interaction among nanocrystalline grains via
the intervening amorphous grain boundary phase results in
improving soft magnetic properties. Among these materials, the nanocrystalline Finemet alloy with composition of
Fe73.5Si13.5B9Nb3Cu1 has found wide applications in
generators and magnetic sensors [1–3]. It was shown that
the role of Cu and Nb played to maximize the density of
crystal nuclei and to retard grain growth, respectively,
leading to an ultrafine grain structure. Consequently,
ultrasoft magnetic properties of Finemet alloy are obtained
[1,2]. The influence of partial substitution of Fe with
various alloying elements in Finemet alloy has been widely
investigated. It was found [4] that the partial substitution

ÃCorresponding author. Tel.: +82 43 2612269; fax: +82 43 2756415.

E-mail address: (S.C. Yu).
0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmmm.2006.01.159

of Fe by Co leads to the increasing of magnetic moment
and Curie point of the amorphous phase. In the previous
report, we have studied the crystallization in Finemet with
Ag substituted for Cu [5] and showed that the crystallization of a-Fe(Si) phase is more stronger than that in pure
Finemet.
In this paper, we present our study on the influence of
annealing temperature and annealing time on the soft
magnetic properties and magnetoimpedance effect of
Finemet Fe73.5Si13.5B9Nb3Au1 alloy.
Amorphous ribbon (7 mm wide, 16.8 mm thick) with
nominal composition Fe73.5Si13.5B9Nb3Au1 was obtained

by rapid quenching from the melt spinning technique. The
crystallization behaviors of the samples were investigated
by DSC (SDT-2960 TA Instruments) measurements. The
phase structure of both as-quenched and annealed samples
was examined by X-ray diffractometer (D5005, Bruker).
For MI measurement the external field applied by a
solenoid can be swept through the entire cycle equally
devided by 800 intervals from À300 to 300 Oe. The
frequency of MI measurement was ranging from 1 to


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N.D. Tho et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e195–e197

10 MHz, and the AC current was fixed at 10 mA for all
measurements.
The XRD pattern for as-quenched ribbon (Fig. 1)
exhibited only one broad peak around 2y ¼ 451, which is
often known as diffuse halo, indicating that the ribbon is
amorphous.
To find out a proper annealing regime for amorphous
ribbon, we carried out DSC measurements (not shown
here). The obtained results show that the substitution of
Cu by Au does not change desirably the shape and
peak position of DSC curves in comparison with those
of Finemet. Namely, there are two exothermal peaks,
the first peak corresponds to the nanocrystallization of
the a-Fe(Si) soft magnetic phase and the second one relates

to the appearance of boride-type phases (Fe3B or Fe2B)
and recrystallization phenomena. It is well known in
Finemet alloy, the roles of Cu to maximize the density
of crystal nuclei of a-Fe(Si) phase and Cu-enriched
regions are observed at the grain boundaries [6].
We suppose that the role of Au in our studied sample is
similar to that of Cu in Finemet. The crystallization
kinetics of ribbon can be observed by measurement of
thermomagnetic curve (not shown here). It was found that
there is single phase structure in the M(T) curve measured
along cooling cycle whereas in case of Ag substituted for
Cu in Finemet, the multiphase structure is observed [5].
Based on the DSC measurements, the ribbon has been
annealed in vacuum at temperature range T a ¼
5202550 1C for different keeping time t ¼ 30, 60 and
90 min to achieve the nanocrystalline material with a-Fe(Si)
phase. The structure of annealed samples has been
determined by XRD, an example for sample optimum
annealed at 530 1C in 90 min is shown also in Fig. 1. The
XRD results indicated that a-Fe(Si) phase is detected in all
samples annealed at different regimes. It is evident that,

upon a proper heat treatment, the as-quenched amorphous
state transformed into bcc nanograins with excellent soft
magnetic properties (mmax has reached 99,000). Using
Scherrer expression, the grain size of crystallites is
determined and showed to be 10.8 nm.
GMI profiles were measured as a function of frequency
and annealing conditions. Fig. 2 presents the MIR of
samples annealed at 530 1C for different keeping time 30,

60 and 90 min, respectively. It was found that the GMI
profiles show a single-peak behavior at low frequency
(f p1 MHz). At frequency below 1 MHz, the maximum
value of GMI was relatively low due to the contribution of
induced magneto-inductive voltage to MI. When frequency
in range 1 MHzpf p5 MHz, the skin effect is dominant, a
higher maximum of GMI value was found. Among the
annealed samples, the highest MIR is observed for sample
annealed at 530 1C in 90 min. This behavior can be
understood that the crystallization volume fraction of aFe(Si) phase increases with increasing of annealing keeping
time. Moreover, the optimal annealing leading to the
lowest value of net magnetostriction of nanocomposite
material, therefore soft magnetic properties are improved
and MIR value is increased.
The PR curves measured in the frequency range for asquenched sample and sample annealed at 530 1C in 90 min
are plotted in Fig. 3. The large changes of magnitude and
field shape of PR in the nanocrystalline alloy compared
with those of as-quenched one indicate that the sample is
ultra softened by crystallization and the structure change
by such annealing has been occurred. The sharpness of PR
curves after annealing implies the decrease of local
anisotropy distribution due to nanocrystallization and also
indicates that the magnetization can be saturated under
very low external field. This behavior is helpful to examine
the soft magnetic properties in nanocrystalline alloy. In

Fig. 1. X-ray diffraction pattern of as-quenched and annealed ribbon:
T a ¼ 530 1C in 90 min.

Fig. 2. The MIR versus the external field H measured in sample annealed

at 530 1C and keeping time 30, 60, 90 min, respectively.


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general, the changes of MI are closely related to the change
of longitudinal incremental permeability. Therefore, the
magnetic softness of material can be estimated from the
MIR or PR profiles.
Research at Chungbuk National University was supported by the Korea Science and Engineering Foundation
through the Research Center for Advanced Magnetic
Materials at Chungnam University. Research at Center
for Materials Science was supported by Vietnam National
Fundamental Research Program, Grant no. 811204.
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Fig. 3. The PR curves of as-quenched sample (a) and annealed sample
(b) versus frequency.