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Magnetic and microwave properties of glass-coated amorphous ferromagnetic microwires 传输线缆及其腹

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Transactions of Nonferrous Metals Society of China

Science Press

Trans. Nonferrous Met. Soc. China 17(2007) 1352-1357

Magnetic and microwave properties of glass-coated amorphous ferromagnetic microwires
D1 Yong-jiang(@,&?I), JIANG Jian-jun(?I@%), DU Gang($* TIAN Bin( Kl BIE Shao-wei(Xq&{$), HE Hua-hui(lnT%$$)



Department of Electronic Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, China Received 15 July 2007; accepted 10 September 2007
Abstract: Glass-coated amorphous FeCuNbSiB microwires were prepared by Taylor-Ulitovsky technique. X-ray diffractometry and scanning electron microscopy were used to investigate the microstructure and morphology of the glass-coated microwires respectively. The vibrating sample magnetometer and vector network analyzer were used to study the magnetostatic and microwave properties of glass-coated microwires. The experimental results show that the effective anisotropy of an array of 150 microwires of 10 mm in length is large than that of one microwire of 10 mm in diameter and an array of 150 microwires of 1 mm in diameter. The natural ferromagnetic resonance takes place as the microwave magnetic component is perpendicular to the microwires axis, and the electric dipole resonance takes place as the microwire is long or the short microwire concentration is moderate. The natural ferromagnetic resonance shifts to higher frequency with the larger microwire concentration. The electric dipole resonance is governed by the microwires length and concentration. The glass-coated FeCuNbSiB microwires can be used to design EM1 filters and microwave absorbing materials.

Key words: glass-coated amorphous microwires; magnetic property; magnetic microwires-dielectric composite; natural ferromagnetic resonance; electric dipole resonance

1 Introduction
The magnetic properties of glass-coated microwires and microwave characteristics of magnetic wiresdielectric composites have received considerable attention due to their much application as magnetic sensors and potential applications as microwave materials and radio absorbing materials in recent years [ 1-31. The amorphous magnetic alloy has outstanding magnetic properties[4-61. The investigation showed that there are length effect[7] and dipolar effect[8] for the magnetic microwires. Other studies showed that the effective permittivity or permeability of microwires-dielectric composites exhibits characteristics of resonance or relaxation when the composites were excited by the electromagnetic wave[9], but the effect of various microwires length and concentration on the microwave properties was not considered. In the study of microwave

properties of wires-dielectric composites[ lo], no coupling between the wires was taken into account. To design microwave absorbing materials, glasscoated alloy microwires of various lengths and concentrations need to be selected to meet the requirements of particular applications. The objective of this work is to investigate the magnetostatic and microwave properties of glass-coated FeCuNbSiB microwires. The effect of microwires concentration and arrange on the microwave properties is analyzed. The mechanisms of natural ferromagnetic resonance(NFMR) and electric dipole resonance(EDR) of the glass-coated FeCuNbSiB microwires-dielectric composites are discussed.

2 Experimental
The glass-coated Fe735CuIo N ~ ~ . ~ S ~ ~ ~ . ~ B ~ microwires were prepared by the Taylor-Ulitovsky technique [ 1 11. The microwires were quenched by tap water with a

Foundation item: Project(5037 1029) supported by the National Natural Science Foundation of C,hina: Project(NCET-04-0702) supported by the New Century Excellent Talents in University, China Corresponding author: J l ANG Jian-jun; Tel: +86-27-87544472; E-mail: jiangjj@rnail.hust.edu.cn

DI Yong-jiang, et aliTrans. Nonferrous Met. Soc. China 17(2007)


cooling rate of 105-106 K/s during the preparation. The structures of the microwires were characterized by X-ray diffractometry(XRD, XPert PRO, Cu K,, 40 kV, 40 mA) and scanning electron microscopy (SEM, Philips Quanta 200,200 kV). The magnetostatic properties were measured by Vibrating Sample Magnetometer (VSM) of Model 3472-70 GMW. The studied number of 10 mm-long microwire was 1 and 150. The length of an array of 150 measured microwires placed side by side with their axis parallel to each other was 10 mm and 1 mm, respectively. In these hysteresis figures, “/I” refers to the longitudinal magnetization with the external magnetic field applied along the microwires axis, and “ ” refers to the I transverse magnetization with the external magnetic field applied perpendicularly to the axis of the microwires. The investigated composites having the form of cylindrical toroidal rings were prepared by bonding the microwires with rubber dissolved by acetone. The dimension of cylindrical toroidal composites is 3.04 mm in inner diameter, 7 mm in outer diameter and 3-4 mm in thickness. Two groups of composites were prepared [9,12-131: the A-type composites Al, A2, and A3 were made by dispersing short microwires of 1-2 mm long randomly to rubber with microwires mass fractions of I%, 15% and 25%, respectively; the B-type composites with a multithread coil-like structure of 50-80 mm microwires have the form of cylindrical toroidal rings with microwires mass fractions of 5%, 15% and 25%, respectively (Fig. 1). The TIR coaxial line method was used to determine the relative complex permeability ,uCt=p’-j,u’’and relative complex permittivity E=d-jt.‘‘ of the composite samples with a HP8722ES vector network analyzer in the frequency range of 2-18 GHz. The maximal mass fraction of microwires in composite was 25% for the glabrous surface of coaxial composite samples with larger mass fraction was difficult to keep.

Fig.1 Schematic structure of samples: (a) Isotropic A-type samples; (b) Anisotropic B-type sample

3 Results and discussion
3.1 Phase structure of microwires Fig.2 shows the X-ray diffraction patterns of glass-coated FeCuNbSiB microwires. No phase peak is observed in the XRD pattern, which implies that the glass-coated microwires are amorphous. As can be seen from the SEM photograph(Fig.3), the diameter of the glass-coated microwires is 4.5 pm in metal core and 8 pm in glass-coating. The geometry of glass-coated microwires is successive and uniform with smooth surface and solid structure.

1 20




50 60 2ei(“)




Fig.2 XRD pattern of glass-coated FeCuNbSiB microwires

3.2 Magnetic properties of microwires As illustrated in Fig.4, the hysteresis curve of a

single Fe-rich microwire exhibits typical squared loop with coercive force of 120 N m , which is associated with the magnetic domain reversal of the metal inner core. As well known, the Fe-rich microwires have a longitudinally magnetized inner core and a radially magnetized thin outer she11[14-15]. The radius of the inner core, Ri, can be estimated according to the following equation:


DI Yong-jiang, et al/Trans. Nonferrous Met. SOC. China 17(2007)
1.0 -

0.5 -

--- L=l nim



H/( 105A Sm-1)



Fig.3 SEM photograph of glass-coated FeCuNbSiB microwires

Fig.5 High field axial and radial hysteresis loops of an array of 150 microwires with samples length of 1 and I0 mm


2 $



As the microwires are of limited length, a decrease in this length for an array of given microwires results in an increase in demagnetizing factor and hence a reduction in the ratio of the volume of the axially magnetized inner core to the total volume of the metallic wire. Thus the axial coercive field H, and anisotropy field Ha along axis decrease.





-0.4 0 0.4 H/( 103A. m- 1 )



Fig.4 Axial hysteresis loop of one microwire with its axis

parallel to external magnetic field

where R, is the radius of the metal core, M$Ms is the remnant to saturation ratio of one microwire, which takes 0.8 according to Fig.4. So it can be estimated that the thickness of thin outer shell is about 0.2 pm. The magnetic properties of an array of microwires depend on their length, as can be seen from Fig.5. The central part of hysteresis loops of all the samples corresponds to domain reversal of the metal inner cores. While the external part of the loops is dominated by domain rotational mechanism of the outer shell and the tangled domain of the metal core ends[ 161. The magnetizing difference of one microwire and an array of microwires can be attributed to the influence of the long-range dipolar-dipolar interaction. When the microwire number increases to about 10, the dipolar interaction gives rise to an additional axial anisotropy, which results in a huge increase of H, along the axis of the microwires[8]. This consequently would influence the macroscopic electromagnetic response of the system.

3.3 Microwave permeability of microwires The complex permeability spectra of the two types of composite with different microwires concentration and arrange orientation in the frequency range of 2-18 GHz are shown in Figs.6 and 7. Both the real and imagine part of permeability rise with the increase of the microwires concentration for both two types of composites. There exist some magnetic resonance for the composite containing high microwire concentration. The natural ferromagnetic resonance(NFMR) comes from the precession of the magnetic moment driven by the microwave magnetic field in an effective magnetic anisotropy field.





I0 12 f/GHz




Fig.6 Permeability of composites with 1 mm long randomly oriented microwires versus frequency

DI Yong-jiang, et al/Trans. Nonferrous Met. SOC. China 17(2007)


1 --'(BI) 2 - pf(B2) 3 - y(B3)

4 -p"(B I ) 5 - &"( B2)

In the excitation of microwave, there is magnetic component in the radial direction of most microwires of A-type composite. The moment of the microwires being most axially magnetized is excited by the microwave, resulting in the precession of the magnetic moment. Thus the NFMR takes place in especial frequency of fr depending on the effective anisotropy field Ha. The ferromagnetic resonance frequency fr of glass-coated microwires can be calculated without external magnetic field (H=O) and Ha<<4xw3]:










where g is the gyromagnetic ratio of 2.21 X IO5III/(A.s), A is magnetization taken as 1.1 T, Ha is the anisotropy 4 Fig.7 Permeability of composites with microwire wound round field. The effective anisotropy field for one microwire is coaxial coil versus frequency about 2 400 Aim, and that for an array of 150 microwires is about 6 000 Aim. The high anisotropy field causes the The magnetic resonance frequency shifts to higher high NFMR frequency that is in the range of 4-12 GHz. frequency with higher microwire concentration. The real The length of short microwires of 1-2 mm is close permeability of samples A1 is very low, while the to the critical length of the microwires for the imagine permeability is a little higher than zero with one demagnetizing energy destroys the uniformly magnetized weak resonance peak at 4 GHz. For sample A2 the domain of the inner core. The Ha of the short microwires average permeability shows a dispersive form in its real component and an obvious magnetic absorbing peak in is non-uniform and less than that of the long microwire, its imaginary component. The complex permeability resulting in the broadening of the resonance half-width. shows strong dispersion when the mass fraction of The permeability spectra of the B-type composite A-type composite increases to 25%. may be partly from the non-strictly circumferential The complex permeability of sample B1 is similar arrangement and non-uniform lengths of the microwires. to that of A1 but having faster falling real component There is also a thin outer shell and tangle magnetized and basically invariable imaginary component. For domain in the two ends of the microwires that have low sample B2 the magnetic resonance is irregular, as effective anisotropy field. There is little part of magnetic displayed in Fig.7. As the mass fraction increases to 25%, moments being perpendicular to the microwave magnetic the resonance increases with more complicated field. Thus there is magnetic resonance instead of frequency dispersion. The values of p' for all of the two continuous reduction of the permeability, as illustrated in types of composite decrease with the increase of the Fig.7. frequency due to the eddy current loss and ferromagnetic With the increase of the microwire concentration in resonance[ lo]. the composite, the distance between the microwires is The skin depth S of the electromagnetic wave in the shortened. So the stronger dipolar interaction causes the microwires can be calculated with the following increase of the effective anisotropic field Ha.Therefore equation: the resonance frequency rises with the increase of the microwires concentration. For A-type of composite, the length 1 of microwires is in a certain range (1-2 mm). The microwires length I where w is the angular frequency, cr is the conductivity is comparable to l,ff/2 (Iefl is the effective wavelength of of 0.8 X 10' S/m, p is the intrinsic permeability taken as the electromagnetic field in the composite). The 5.5-6.5i at 5 GHz for the amorphous Fe73.5Cul.oNb3.0- geometric resonance may be take place in some Si13.5B9,0 microwires. Thus 6 for the microwires at 5 GHz frequency. is about 2.73 pm, larger than 0.2 pm of outer shell of the alloy core. At the NFMR frequency, p suddenly increases 3.4 Microwave permittivity of microwires by some times, causing 6 value to decrease but still larger Resonance or relaxation type of permittivity spectra than the outer shell. So the microwave magnetic field can can be seen from Figs.8 and 9 for different microwires penetrate most of the inner metal core and consume large concentration and structure. The values of both E' and d' part of microwave magnetic energy in the measured for composite A2 are higher than those of A1 and far frequency range. lower than those of A3. The dielectric absorption changes



DI Yong-jiang, et al/Trans.Nonferrous Met. Soc. China 17(2007)

1 -&’(Al) 2 -&!(A2) 3-E‘(A~)

4-~”(Al) 5 -~l’(A2) 6 &”(A3)


.............. .............

==z -






1 1




10 12 JlGHz




Fig.8 Permittivity of composites with 1 mm long randomly oriented microwires versus frequency


1 -&‘(Bl) 2-~‘(B2) 3 -E’ ( B3)

4-&”(Bl) 5-&’(B2) 6 E”( B3)


.i 30
5 .c

r : u 0 u

7. 2


EDR frequency is inverse with the length of microwires. There is EDR for the long microwires in 2--18 GHz. The electric response is intensified for the interaction between the microwires in the composite with the high microwire concentration, resulting in the increase of the permittivity. Thus the permittivity shifts to higher frequency and the dielectric absorption peak broadens with larger mass of microwires. The permittivity of short microwire composite is complicated. The permittivity of A-type composite with high microwires concentration is some like the randomly distributed conductive fiber-dielectric composite. For the composite with dilute short microwires, the permittivity decreases with increasing the measured frequency. As the short microwire concentration is not very low, such as sample A I, the moderate electric interaction between the radiant electromagnetic wave may result in the resonance of the permittivity. When the microwire concentration is high enough, the shortened distance between the microwires causes the increase of the contact probability between the microwires. Thus the intense metallicity of the microwire composites may result in the negative real permittivity.



4 Conclusions
10 0
2 4



10 12 f’lGHz




Fig9 Permittivity of composites with microwire wound round

coaxial coil versus frequency from resonance-type to relaxation-type with the increase of the microwires concentration. The alloy microwires behave as electric dipole in the excitation of the microwave electric field. The collective oscillation of free electrons is excited by the microwave electric field, generating the line current in the microwires. Thus the microwires consume the incident electromagnetic energy and cause the occurrence of electric dipole resonance(EDR) at given frequency, which is like micro-antennas. The EDR frequency of the composite with low microwires concentration is expressed as[ 171:

1) The anisotropy of an array of long glass-coated amorphous Fe73.5C~I ONb3.0Si13 9 .microwires is higher sB ~ than that of an array of short amorphous microwires. 2 ) The electromagnetic properties depend on the microwires concentration and arrange orientation. The microwave permeability and permittivity of composite increase with the increase of the microwire concentration. 3) The NFMR is more remarkable for the randomly distributed microwires-dielectric composite. The EDR takes place as the long microwires are parallel to the microwave electric field. The NFMR and EDR frequency of composites shift to higher frequency with the higher microwire Concentration. 4) The high microwave electromagnetic loss of glass-coated Fe-rich microwires makes them be used as EM1 filters and applied to develop microwave absorbing materials.

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where fres,” is the EDR frequency, c is the light velocity, n is natural number, 1 is the microwire length, E is the permittivity of matrix taken as 2. The first electric dipole resonance frequency is at the lowest frequency with a maximal response. As can be seen from Eqn.(4), the



DI Yong-jiang, et al/Trans. Nonferrous Met. SOC. China 17(2007)
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