Hoaa 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 Dep
Trang 1Journal of Magnetism and Magnetic Materials 304 (2006) e871–e873
A systematic study of giant magnetoimpedance of Cr-substituted
Fe 73.5x Cr x Si 13.5 B 9 Nb 3 Au 1 (x ¼ 1, 2, 3, 4, 5) alloys
N.D Thoa, N Chaua, S.C Yub, , H.B Leec, N.D Thea, N.Q Hoaa
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 27 March 2006
Abstract
The magnetoimpedance of Fe76.5xCrxSi13.5B9Nb3Au1 (x ¼ 1, 2, 3, 4, 5) alloys has been measured to investigate the influence of crystallization process on the soft magnetic properties and magnetic anisotropy after thermal treatment Annealing performed at 540 and
550 1C for 30 min in a vacuum indicated that ultrasoft magnetic properties of nanocomposite materials are obtained The magnetoimpedance ratio (MIR) and incremental permeability ratio (PR) measurements show that the maximum values of MIR and
PR increase drastically in the heat-treated samples It means that the samples are softened by nanocrystallization The PR curves become narrower and sharper due to the decrease of anisotropy The MIR behavior related with the softness of magnetic properties of heat-treated samples and the incremental PR strongly changes with external magnetic field
r2006 Elsevier B.V All rights reserved
PACS: 75.50.Tt
Keywords: Amorphous; Nanocrystalline; Magnetoimpedance; Permeability
The magnetoimpedance (MI) effect is the change of the
impedance experienced by an AC current flowing through
a magnetic material when an external DC magnetic field is
applied In recent years, many works on MI effect has
stimulated considerable attention because of its
technolo-gical applications in magnetic sensors and devices[1,2] The
influence of various substituting alloying elements for Fe in
FeCuNbSiB composition has been also widely investigated
Recently, it has been reported that the partial substitution
of Fe by Cr enhances the thermal stability of the
amorphous alloy against nanocrystallization and lowers
the Curie temperature of both, as-cast amorphous alloys
and the residual amorphous phase in the nanocomposite
[3] Other authors [4] have found that partially
substitu-ting Fe by Co in Fe73.5xCoxSi13.5B9Nb3Cu1 alloys leads
to the increasing of magnetic moment and the Curie
point of precipitated crystalline phase More recently,
it was reported that the Cr substitution in Fe-based
amorphous alloys can also improve the mechanical or electrical properties without deteriorating the magnetic properties [5]
In this study, we systematically investigate the giant magnetoimpedance (GMI) effect and the effect of Cr substitution for Fe on the soft magnetic properties of
Fe73.5xCrxSi13.5B9Nb3Au1 (x ¼ 1, 2, 3, 4, 5) alloys with different annealing temperatures
Amorphous ribbons (7 mm wide, 16.8 mm thick) with nominal compositions Fe73.5xCrxSi13.5B9Nb3Au1 (x ¼ 1,
2, 3, 4, 5) were obtained by rapid quenching from the melt spinning technique The crystallization behaviors of the samples were investigated by DSC (SDT-2960 TA Instru-ments) measurements The phase structures of both as-quenched and annealed samples were examined by X-ray diffractometer (D5005, Bruker) 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 MI measurement was ranging from 1 to 10 MHz, and the AC current was fixed at 10 mA for all measurements
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0304-8853/$ - see front matter r 2006 Elsevier B.V All rights reserved.
doi:10.1016/j.jmmm.2006.03.021
Corresponding author Tel.: +82 43 2612269; fax: +82 43 2756415.
E-mail address: scyu@chungbuk.ac.kr (S.C Yu).
Trang 2The X-ray diffraction analysis shows that the
as-quenched samples are amorphous The DSC measurements
on the as-quenched ribbons were performed at a heating
rate of 20 1C/min The results indicate that the
devitrifica-tion of the investigated alloys takes place in two main
stages The first one corresponds to the crystallization of
the a-Fe(Si) soft magnetic phase, while the second is related
with the appearance of boride-type phase (Fe3B or Fe2B)
It was found that the addition of Cr produces a slight
stabilization of the amorphous alloy against the
crystal-lization, which can be detected as a linear increase of the
peak temperature of the first exothermal The MIR as a
function of the applied field, H, is defined with respect to
the maximum applied field (Hmax¼300 Oe in the present
work) as DZ/Z(%) ¼ DZ/Z(Hmax) ¼ 1|Z(H)/Z(Hmax)|
The PR can be defined as PR(H) ¼ Dm/m (Hmax) ¼ 1|m
(H)/m (Hmax)|
In amorphous ribbon materials, the MI effect is favored
by the decrease of resistivity resulting from the
crystal-lization process This strong reduction in the resistivity of
the nanocrystalline ribbons reduces the skin depth and
increases the MIR of the samples[6] From the nearly zero MIR values in the as-quenched samples it is evident that the samples do not show soft magnetic properties However, the maximum MIR value increases drastically
in the samples annealed at 540 and 550 1C, indicating that the studied samples are ultra-softened by the crystal-lization, see example inFig 1for sample with x ¼ 4 From
Fig 1, the frequency dependence of MIR in the samples shows a typical behavior where the shapes of the MIR curves are generally getting broader with the increment of the measuring frequency throughout all samples The rather high values and sharpness of the MIR curves in the annealed samples compared to the as-quenched ones indicate that structure changes such as the nanocrystalliza-tion have occurred in the annealed samples Among the investigated samples, the largest GMI effect was observed
in the nanocrystalline sample containing 5% of Cr (x ¼ 5) and reached the value of 190% at frequency of 2 MHz This is ideal for developing high-performance magnetic sensor
The MI effect at high frequency can be explained in terms of an external field dependence of impedance as a result of the circumferential magnetization with respect to
Fig 1 The MIR versus the external field H measured at various
frequencies in Fe 72.5 Cr 4 Si 13.5 B 9 Nb 3 Au 1 alloy annealed at (a) 540 1C and
(b) 550 1C.
Fig 2 The PR curves of as-quenched samples and the annealed samples
Fe Cr Si B Nb Au (x ¼ 1, 2, 3, 4, 5) measured at 1 MHz.
Trang 3the current direction running through the sample and the
skin effect of AC current At the frequency below 1 MHz,
the maximum value of GMI was relatively low (not shown
here) and we suppose that it is due to the contribution of
the induced magnetoinductive voltage to MI[6] When the
frequency is in the range 1 MHzpfp5 MHz, skin effect is
dominant and larger GMI values were found The highest
MI ratio is observed for nearly zero saturation
magnetos-triction after annealing at about 550 1C At this annealing
temperature the effective magnetostriction is fully
compen-sated so that the effective magnetoelastic anisotropy is
minimum Moreover, transverse magnetic anisotropy is
additionally induced on the ribbon’s surface during the
annealing process This typical anisotropy controls the
magnetization vector in the transverse domain and thus
improves the magnetic response of the soft magnetic
nanocrystalline material Therefore, the GMI effect is
enhanced as a direct consequence of the higher mobility of
domain walls as correlated with transverse permeability[6]
The PR curves measured at 1 MHz in the as-quenched
samples and the samples annealed at 550 1C are plotted in
Fig 2 The large changes of the magnitude and field
shape of the PR in the nanocrystalline alloys compared
with as-quenched samples indicate that structural change
such as crystallization has occurred To determine the
structural changes of the samples, X-ray diffraction
measurements have been performed The X-ray patterns
show the appearance of a-Fe(Si) peaks in the annealed samples The sharpness of PR curves after annealing implies the decrease of local anisotropy distribution by the nanocrystallization and indicates that the magnetization can be saturated under very low external field In general, the changes of the MI are closely related to the changes
of the longitudinal incremental permeability Therefore, magnetic softness can be estimated from the MIR or the PR
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] R.S Beach, A.E Berkowitz, Appl Phys Lett 76 (1994) 6209 [2] R.L Sommer, C.L Chien, Appl Phys Lett 67 (1995) 3652 [3] J Fuzer, P Matta, P Kollar, P Sovak, M Konc, J Mag Mag Mater 158 (1996) 205.
[4] N Chau, N.X Chien, N.Q Hoa, P.Q Niem, N.H Luong, N.D Tho, V.V Hiep, J Mag Mag Mater 282 (2004) 174.
[5] N Bayri, H.I Adiguzel, S Atalay, P Sovak, Phys Status Solidi A 189 (2002) 805.
[6] M Knobel, M.L Sanchez, C Gomez-Polo, P Marin, M Vazquez,
J Appl Phys 79 (1996) 1646.