Journal of Magnetism and Magnetic Materials 304 2006 e195–e197Annealing effect on soft magnetic properties and magnetoimpedance N.D.. Tuanc a Center for Materials Science, Vietnam Nation
Trang 1Journal of Magnetism and Magnetic Materials 304 (2006) e195–e197
Annealing effect on soft magnetic properties and magnetoimpedance
N.D Thoa, N Chaua, S.C Yub, , 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 Fe73.5Si13.5B9Nb3Au1amorphous 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
r2006 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
Magnetic interaction among nanocrystalline grains via
the intervening amorphous grain boundary phase results in
improving soft magnetic properties Among these
materi-als, 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
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 crystal-lization 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 Fe73.5Si13.5B9Nb3Au1alloy
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 300 to 300 Oe The frequency of MI measurement was ranging from 1 to
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0304-8853/$ - see front matter r 2006 Elsevier B.V All rights reserved.
doi: 10.1016/j.jmmm.2006.01.159
Corresponding author Tel.: +82 43 2612269; fax: +82 43 2756415.
E-mail address: scyu@chungbuk.ac.kr (S.C Yu).
Trang 210 MHz, and the AC current was fixed at 10 mA for all
measurements
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
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
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
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
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
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 a-Fe(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 as-quenched sample and sample annealed at 530 1C in 90 min are plotted inFig 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 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.
Trang 3general, 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 sup-ported 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 References
[1] Y Yoshizawa, S Oguma, K Yamauchi, J Appl Phys 64 (1988) 6044 [2] P Marin, A Hernando, J Magn Magn Mater 215 (1995) 729 [3] D.C Jiles, Acta Mater 51 (2003) 5907.
[4] N Chau, N.X Chien, N.Q Hoa, P.Q Niem, N.H Luong, N.D Tho, V.V Hiep, J Magn Magn Mater 282 (2004) 174.
[5] N Chau, N.Q Hoa, N.H Luong, J Magn Magn Mater 290–191 (2005) 1547.
[6] K Hono, D.H Ping, S Hirosawa, MRS Symp Proc 577 (1999) 507.
Fig 3 The PR curves of as-quenched sample (a) and annealed sample
(b) versus frequency.