The measurements of thermomagnetic curves indicated that the Curie temperature of the amorphous phase of the samples decreased with increasing Mn content.. Tt Keywords: Nanocrystalline;
Trang 1Journal of Magnetism and Magnetic Materials 304 (2006) e868–e870
Soft magnetic behaviour in amorphous and nanocrystalline
Fe 73.5x Mn x Si 13.5 B 9 Nb 3 Cu 1 (x ¼ 1, 3, 5) alloys N.D Thoa, N Chaua, S.C Yub, , H.B Leec, L.A Tuanc, N.Q Hoaa
a Center for Materials Science and Faculty of Physics, Hanoi University of Science, 334 NguyenTrai, Hanoi, Vietnam
b Department of Physics, Chungbuk National University, Cheongju 361-763, Republic of Korea c
Departement of Physics, Kongju NationalUniversity, Kongju 314-701, Republic of Korea
Available online 27 March 2006
Abstract
Amorphous ribbons Fe73.5xMnxSi13.5Nb3Cu1(x ¼ 1, 3, 5) were prepared by rapid quenching on a single rotated copper wheel The X-ray patterns show that the as-cast samples are amorphous The measurements of thermomagnetic curves indicated that the Curie temperature of the amorphous phase of the samples decreased with increasing Mn content The optimal heat treatment was performed at
Ta¼535 1C for 1 h and showed that the ultrasoft magnetic properties of nanocomposite materials were obtained The frequency dependence of magnetoimpedance was measured in the frequency range of 1–10 MHz and at a fixed current of 10 mA The correlation between the MI effect and the soft magnetic properties is discussed
r2006 Elsevier B.V All rights reserved
PACS: 75.50 Tt
Keywords: Nanocrystalline; Amorphous; Magnetoimpedance; Permeability
Soft magnetic properties of Fe-rich nanocrystalline alloy
Fe73.5Si13.5B9Nb3Cu1, namely, FINEMETs materials [1]
have been extensively studied during the last decade[2] The
increased interest in the study of the alloys arises from a
wide applications found in saturable reactor, generators,
transformer and magnetic sensors [3] The influence of
partial substitution of Fe with various alloying elements
(Co[4], Cr[5]) in Fe73.5Si13.5B9Nb3Cu1alloy has been widely
investigated They found that the partial substitution of Fe
by Cr could improve the mechanical or electrical properties
without deteriorating magnetic properties while substitution
for Fe by Co leads to the increase of magnetic moment and
Curie point of the precipitated crystalline phase
Recently, it was reported that the partial substitution of
Fe by Mn in Fe-based amorphous alloys can also improve
the coupling between grains and AC permeability, but
leads to reduction of the exchange coupling between the
crystalline and residual amorphous phase[6]
The aim of the present work is to investigate the influence
of partial substitution of Fe by Mn on the magnetic properties of the Fe73.5xMnxSi13.5B9Nb3Cu1 (x ¼ 1, 3, 5) alloys The correlation between the MI effect and soft magnetic properties of these ribbons is also discussed Amorphous Fe73.5xMnxSi13.5B9Nb3Cu1 (x ¼ 1, 3, 5) alloys were prepared by melt–spinning technique The ribbon is 8 mm wide and about 20 mm thick The structure
of the as-cast and annealed samples was examined by a Bruker 5005 X-ray diffractometer The crystallization phases were examined by differential scanning calorimetry (DSC) using SDT 2960 TA Instrument The magnetic properties of the ribbon were measured in a DMS 880 VSM and a Walker Permagraph AMH 20 For the MI measurement the external field applied by a solenoid can be swept through the entire cycle equally divided by 800 intervals from 300 to 300 Oe The frequency of the MI measurement ranged from 1 to 10 MHz, and the AC current was fixed at 10 mA for all measurements
Firstly, we examined the structure of the as-quenched samples by using OLE_LINK1XRDOLE_LINK1y ¼ 451 indicating the amorphous nature of the as-cast samples
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0304-8853/$ - see front matter r 2006 Elsevier B.V All rights reserved.
doi:10.1016/j.jmmm.2006.03.020
Corresponding author Tel.: +82 43 2612269; fax: +82 43 2756415.
E-mail address: scyu@chungbuk.ac.kr (S.C Yu).
Trang 2We carried out DSC measurements in order to
char-acterize the crystallization process and found out the
proper annealing temperature for the as-quenched
amor-phous ribbon
Fig 1 shows the DSC curves of the as-quenched
amorphous ribbon with a heating rate of 20 1C/min and
from room temperature to 800 1C As observed in Fig 1,
the crystallization process of the investigated alloys take
place in two main steps The first one corresponds to the
nanocrystallization of the a-Fe(Si) soft magnetic phase,
while the second is related to the appearance of boride-type
phases (Fe3B or Fe2B) and recrystallization phenomena[6]
The crystallization temperature of the a-Fe(Si) phase (Tp1)
in all samples studied is higher than that of the original
FINEMETs alloy It shows that the addition of Mn
clearly exerts a stabilizing effect on the amorphous alloys
against nanocrystallization As observed also inFig 1, the
Tp1increases almost linearly with Mn content in the range
of the composition studied This implies that the existence
of Mn to certain extent weakens the diffusion process to
form the crystalline phase
We used the Kissinger method [7] to quantify the
crystallization kinetics of a continuous heating and found
out the crystallization activation energy values of a-Fe(Si)
phase in the present alloys The values of activation energy
were found to decrease from 3.1 eV (x ¼ 1) to 2.8 eV
(x ¼ 3) and to 2.6 eV (x ¼ 5) (not shown here) for the
a-Fe(Si) phase
In order to study the crystallization kinetics, we
measured thermomagnetic curves of the amorphous
samples Fig 2 shows the magnetization versus
tempera-ture for the sample with x ¼ 1 From the thermomagnetic
curves, it can be seen that the Curie temperature of
amorphous phase of the samples decreases with increasing
of Mn content, namely TC¼342 1C (x ¼ 1), TC¼310 1C (x ¼ 3) and TC¼281 1C (x ¼ 5)
It means that the Curie temperature of the amorphous phase in the samples studied is reduced because Mn interacts antiferromagnetically with Fe as reported in Ref [8] The influence of partial substitution of Fe by
Mn and heat treatments on the magnetic properties was also studied by measurements of magnetic hysteresis loops and magnetization curves It was found that the presence of Mn has a noticeable effect on the shape of the magnetic hysteresis loops, causing a decrease in coercivity and maximum magnetization in the as-quenched amor-phous samples and annealed samples The magnetization curves were measured for both as-cast as well as annealed samples (not shown here) The results indicated that saturation magnetization also decreases with increasing
Mn content
The magnetoimpedance ratio (MIR), can be defined as DZ/Z (%) ¼ Z(H)/Z(Hmax)1, where Hmax is external magnetic field sufficient to saturate the impedance and equals to 300 Oe in the present study The giant magne-toimpedance effect can be observed only in ultrasoft magnetic materials with nearly zero magnetostriction constant, nearly zero coercivity, and high circumferential permeability The nearly zero MIR value in as-quenched samples is evident that the samples are not ultrasoft However, the maximum MIR value increases drastically in the samples annealed at 535 1C It is indicated that the samples are softened by nanocrystallization, an example shown inFig 3with x ¼ 1 The results obtained show that the values of MIR increase with increasing Mn content The permeability ratio (PR), is also plotted in Fig 4as a function of the external field One notes that the changes of the magnetoimpedance are much related to the changes of
150 300 450 600 750 900
564°C
563 °C
562°C
676°C 673°C 671°C
Temperature (°C)
x=1 x=3 x=5
Fig 1 DSC patterns of as-cast Fe73.5xMnxSi13.5B9Nb3Cu1 (x ¼ 1, 3, 5)
ribbons.
0 30 60 90 120
(2) (1)
T (°C)
H = 20 Oe
Fe 72.5 Mn 1 Si 13.5 Nb 3 B 9 Cu 1
(a)
Fig 2 Thermomagnetic curves of ribbon with x ¼ 1 (1: heating cycle, 2: cooling cycle).
Trang 3longitudinal permeability in the presence of an external
field The sharpness of PR curves after annealing implies
the decrease of the local anisotropy distribution by
nanocrystallization This behaviour is helpful to examine
the soft magnetic properties of the present alloys
Research at Chungbuk National University was
sup-ported by Korea Research Fundamental Grant no
KRF-2003-05-C00018 Research at Center for Materials Science
was supported by Vietnam National Fundamental
Re-search Program Grant no.421004
References
[1] Y Yoshizawa, S Oguma, K Yamauchi, J Appl Phys 64 (1998) 6044 [2] G Herzer, Master Sci Eng A 133 (1999) 1.
[3] D.C Jiles, Acta Master 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] A Pardo, E Otero, M.C Merino, M.D Lopez, M Vazquez Crros Sci 43 (2001) 689.
[6] C Gomez-Polo, J.I Perez-Landazabal, V Recarte, P.M Zelis, Y.F.
Li, M Vazquez, J Magn Magn Mater 290–291 (2005) 1517 [7] L.V Meisel, P.J Cote, Acta metal 31 (1983) 1053.
[8] K Ashok, I Sinha, Appl Phys 42 (1971) 338.
-300 -200 -100 0 100 200 300
0
10
20
30
40
50
10 mA
20 mA
30 mA
H (Oe)
f=1MHz
x = 1
Ta = 535°C in 1h
Fig 3 MIR measured at 1 MHz of the sample with x ¼ 1 as a function of
the external dc field at various ac drive fields.
-300 -200 -100 0 100 200 300 0
5 10 15 20 25 30 35 40
1M Hz 2M Hz 3M Hz 4M Hz 5M Hz
H (Oe)
Fe 72.5 Mn 1 Si 13.5 B 9 Nb 3 Cu 1
T a = 535°C in 1h
i = 10 mA
Fig 4 The PR vs the external field H for sample with x ¼ 1, annealed at
535 1C for 1 h.