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Frequency response engineering of CoFeNiBSi microwires in the gigahertz range
Journal of Magnetism and Magnetic Materials 242–245 (2002) 247–250
Frequency response engineering of CoFeNiBSi microwires in the gigahertz range S. Deprota,b,*, A.L. Adenota, F. Bertina, O. Achera b
a CEA Le Ripault, BP16, F-37260 Monts, France LEMA, Universit!e Franc-ois Rabelais, Parc de Grandmont, F-37200 Tours, France
Abstract Amorphous glass-coated microwires were prepared by the Taylor–Ulitovsky method. We present the tailoring possibilities of their frequency response from 130 MHz to 18 GHz, which depends not only on the composition but also on the dimensional characteristics (metallic core diameter and glass-cover thickness). r 2002 Elsevier Science B.V. All rights reserved. Keywords: Glass-coated amorphous microwires; Parallel permeability; Magnetoelastic anisotropy
1. Introduction The magnetic properties of ferromagnetic microwires have been extensively studied in the last few years due to a great deal of interest for fundamental investigations and their enormous potential in technological applications (sensors, magnetic shieldingy). It has been shown that the magnetic behaviour of the microwires strongly depends on their dimensions and composition, which permits a very good control of their magnetic properties starting from the casting process [1–4]. The aim of this paper is to present some results concerning the tailoring possibilities of their magnetic properties and their parallel microwave permeability in the gigahertz frequency range.
2. Experimental details The amorphous ferromagnetic microwires were cast by the Taylor–Ulitovsky method [5]. This technique consists in drawing a Pyrex-like glass tube containing
*Corresponding author. CEA, LEMA, Universit!e Franc-ois Rabelais, Parc de Grandmont, F-37200 Tours, France. Tel.: +33-2-47-34-55-29; fax: +33-2-47-34-51-79. E-mail address: [email protected] (S. Deprot).
the molten alloy to obtain a continuous metallic nucleus covered by an insulating glass coating. The starting alloys are the amorphous small negative magnetostrictive commercial 2705M alloy from VacuumSchmelze and alloys from the Co75:5x Fex Ni1.5B12Si11 system. We have chosen this alloy system in order to change the magnetostriction coefficient with the Fe/(Fe+Co) ratio. The Co75:5x Fex Ni1.5B12Si11 (x ¼ 2; 3 and 4 at%) master alloys were obtained by induction melting the appropriate amounts of Co, Fe, Ni, B, Si crystalline materials in the argon atmosphere. To ensure a good homogeneity of the alloys, several meltings were performed. The compositions of the produced microwires are presented in Table 1. By changing the casting parameters, the microwires were fabricated with different radii of the metallic nucleus and different thicknesses of the insulating coating. The diameter of the metallic core mainly depends on the winding speed and the drawing temperature. The higher the speed is, the smaller the diameter. The drawing temperature which determines the temperature–viscosity behaviour of the glass plays an important role. The X dependence on temperature drawing is presented in Fig. 1. X is the glass and metal cross-sectional ratio, X ¼ ðdw=dmÞ2 1; where dm is the metallic core diameter and dw the total diameter. As can be seen in Fig. 1, X increases considerably with the
0304-8853/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 1 ) 0 1 2 4 5 - 8
S. Deprot et al. / Journal of Magnetism and Magnetic Materials 242–245 (2002) 247–250
248
Table 1 Composition and magnetic properties of the investigated Co75:5x FexNi1.5B12Si11 microwires with dm ¼ 4 mm and dw ¼ 16 mm. Composition
Label
ls ( 106)
Ha (Oe)
Co71.5Fe4Ni1.5B12Si11 Co72.5Fe3Ni1.5B12Si11 Co 73.5Fe2Ni1.5B12Si11
a b c
1.29 2.08 2.88
43 55 86
650
40
550
Apparent Permeability
45 35
X
30 25 20 15 10 5 0 1200
1220
1240
1260
1280
1300
1320
Temperature (°C) Fig. 1. X dependence on temperature drawing, where X is the glass and metal cross-sectional ratio, X ¼ ðdw=dmÞ2 1:
melt temperature. The total diameter is kept constant (16 mm), whereas the metallic nucleus decreases from 10 to 2.5 mm when the melt temperature increases from 12101C to 13001C. This is attributed to the temperature– viscosity behaviour of the glass. An optical immersion microscope has been employed to check the dimensional characteristics of the wires. Static magnetic characterization was carried out using a vibrating sample magnetometer (VSM). The microwave parallel permeability of the wires was measured in the range 130 MHz–18 GHz. The experimental measurement method consists of winding the glass-coated microwire into a torus and measuring the permeability of the sample using a coaxial line [6]. The apparent permeability ma of the wire is then deduced from the permeability of the composite mjj using the following relation: mjj ¼ qma þ ð1 qÞmm ; where q is the ferromagnetic volume fraction in the sample and mm the permeability of the insulating cover and non-magnetic matrix. The apparent permeability can be described by the coupling of skin effect and of the gyromagnetic permeability. The gyromagnetic resopffiffiffiffiffiffiffiffiffiffiffi nance frequency ðm0 ¼ 1Þ is given by fr ¼ g Bs Ha ; where Bs is the saturation induction, Ha the anisotropy field and g the gyromagnetic ratio. It is not affected by skin effect.
t = 2 µm t = 6 µm
450 350 250 150
µ"
50 -50 0.1 -150
10 µ' Frequency (GHz)
Fig. 2. Apparent relative permeability versus frequency for microwires obtained from the 2705M alloy with the same diameter of the metallic core (4 mm) but two different glass thicknesses (t ¼ 2 and 6 mm).
3. Results and discussion The influence of the stress quenched in the ferromagnetic core due to the difference in thermal expansion coefficients between the metallic nucleus and the glass coating [7] is analyzed by considering microwires with different glass thicknesses. Fig. 2 shows the permeability versus frequency in the gigahertz range for two microwires with the same nucleus diameter (4 mm) but two different thicknesses of coating (2 and 6 mm). It is expected that a thicker coating would lead to larger stresses and to higher values of the induced anisotropy, thus increasing the gyromagnetic resonance frequency. Indeed, for the sample with smaller glass coating thickness, the resonance frequency is at 700 MHz. For the sample with thicker glass coating, the resonance frequency rises to 1 GHz. When the metallic core diameter varies while keeping the total diameter constant, both stress-induced anisotropy and skin effect act on the permeability of the microwire. Fig. 3 shows the permeability of three wires of the same composition with a total diameter equal to 16 mm and metallic core diameter varying from 2.5 to 10 mm. For the 2.5 mm core diameter, the permeability is nearly free of skin effect: m0 is constant up to the neighbouring resonance frequency, and the frequency at which m00 is maximum corresponds to the resonance frequency. When the metallic diameter increases, the
S. Deprot et al. / Journal of Magnetism and Magnetic Materials 242–245 (2002) 247–250
Apparent Permeability
500 400
dm=2.5 µm dm=4 µm dm=10 µm
300 200
µ"
100 0 0.1
1
10
-100 -200
µ' Frequency (GHz)
Fig. 3. Apparent relative permeability versus frequency for microwires obtained from 2705M alloy with the same total diameter (16 mm) but different metallic core diameters dm ¼ 2:5; 4 and 10 mm.
249
evaluated from a relation established in the literature [8]. The values are collected in Table 1. Static magnetic characterizations were performed applying a magnetic field along the wire axis: flat hysteresis loops, typical of an amorphous wire with a negative magnetostrictive coefficient and a magnetic structure with circumferential domains are obtained [9]. Saturation magnetization variation from x ¼ 4 to 2 at% does not exceed 10%, whereas the anisotropy field Ha deduced from the hysteresis loops has been found to vary from 43 to 86 Oe (see Table 1). As expected, a correlation between ls and Ha is observed. The gyromagnetic resonance frequency deduced from the microwave permeability increases from 1.9 GHz for alloy (a) to 2.8 GHz for alloy (c). This is consistent with a growing anisotropy field.
4. Conclusion 250 (a)
Apparent Permeability
200 150
(b)
100
(c) µ"
50 0 0.1 -50 -100
1
10 µ'
Frequency (GHz)
Fig. 4. Apparent relative permeability versus frequency for glass-coated microwires obtained from (a), (b) and (c) alloys with the same metallic diameter (4 mm) and the same total diameter (16 mm).
resonance frequency decreases since the stress-induced anisotropy decreases. Moreover, due to an increase of skin effect, the ‘‘plateau’’ of m0 disappears. The m00 peak is attenuated and the frequency at m00 maximun is different from the resonance frequency. As mentioned in the introduction, the composition of the metallic nucleus plays a fundamental role in the magnetic properties of the microwires. Fig. 4 shows the permeability versus frequency of three wires with compositions a, b and c as reported in Table 1. To allow a comparative study of the composition effect, the geometric characteristics of the wires are similar for the three wires. The metallic core has been chosen equal to 4 mm to limit skin effect. The total diameter is 16 mm. As the wires are obtained in the same experimental conditions, the stresses are considered to be the same for the three wires. The magnetostriction constant ls is
In this paper, we have shown that the microwave response of amorphous glass-coated ferromagnetic microwires can be controlled by the geometric characteristics and the wire composition. The stresses in the ferromagnetic nucleus of the wire depend on the glass to metal cross-sectional ratio. These stresses induce a magnetic anisotropy whose intensity is related to the magnetostriction coefficient of the alloy. We have studied both the influence of the dimensions and of the magnetostriction constant on the microwave magnetic properties of ferromagnetic microwires in the gigahertz frequency range. The stress-induced anisotropy allows us to change the gyromagnetic resonance frequency from 700 MHz to 2.8 GHz, offering the possibility to use these wires in a wide variety of applications. Moreover, the shape of the frequency response of the microwave permeability is modified by the skin effect if the metallic core diameter exceeds 4 mm. Thin metallic core diameter wires are therefore very interesting for the study of the gyromagnetic resonance in these materials.
Acknowledgements The authors are grateful to P. De Rango and D. Fruchart of the Laboratoire de Cristallographie, Grenoble, for providing the alloys.
References [1] A. Zhukov, J. Gonzalez, J.M. Blanco, M. Vazquez, V. Larin, J. Mater. Res. 15 (2000) 2107. [2] A.F. Cobeno, A. Zhukov, J.M. Blanco, V. Larin, J. Gonzalez, J. Mater. Res. 14 (1999) 3775. [3] H. Chiriac, T.A. Ovari, Gh. Pop, F. Barariu, Sensors Actuators A 59 (1997) 243.
250
S. Deprot et al. / Journal of Magnetism and Magnetic Materials 242–245 (2002) 247–250
[4] D. M!enard, A. Yelon, J. Appl. Phys. 88 (2000) 379. [5] G.F. Taylor, Phys. Rev. 24 (1924) 655. [6] P.-M. Jacquart, O. Acher, IEEE Trans. Microwave Theory Tech. 44 (1996) 2116. [7] S. Antonov, V.t. Borisov, O.V. Borisov, A.F. Prokoshin, N.A. Usov, J. Phys. D: Appl. Phys. 33 (2000) 1161.
[8] K. Aso, S. Uedaira, M. Hayakawa, K. Hotai, Y. Ochiai, K. Hayashi, Y. Makino, J. Magn. Magn. Mater. 31–34 (1983) 1546. [9] M. Vazquez, A.P. Zhukov, J. Magn. Magn. Mater. 160 (1996) 223.
Frequency response engineering of CoFeNiBSi microwires in the gigahertz range S. Deprota,b,*, A.L. Adenota, F. Bertina, O. Achera b
a CEA Le Ripault, BP16, F-37260 Monts, France LEMA, Universit!e Franc-ois Rabelais, Parc de Grandmont, F-37200 Tours, France
Abstract Amorphous glass-coated microwires were prepared by the Taylor–Ulitovsky method. We present the tailoring possibilities of their frequency response from 130 MHz to 18 GHz, which depends not only on the composition but also on the dimensional characteristics (metallic core diameter and glass-cover thickness). r 2002 Elsevier Science B.V. All rights reserved. Keywords: Glass-coated amorphous microwires; Parallel permeability; Magnetoelastic anisotropy
1. Introduction The magnetic properties of ferromagnetic microwires have been extensively studied in the last few years due to a great deal of interest for fundamental investigations and their enormous potential in technological applications (sensors, magnetic shieldingy). It has been shown that the magnetic behaviour of the microwires strongly depends on their dimensions and composition, which permits a very good control of their magnetic properties starting from the casting process [1–4]. The aim of this paper is to present some results concerning the tailoring possibilities of their magnetic properties and their parallel microwave permeability in the gigahertz frequency range.
2. Experimental details The amorphous ferromagnetic microwires were cast by the Taylor–Ulitovsky method [5]. This technique consists in drawing a Pyrex-like glass tube containing
*Corresponding author. CEA, LEMA, Universit!e Franc-ois Rabelais, Parc de Grandmont, F-37200 Tours, France. Tel.: +33-2-47-34-55-29; fax: +33-2-47-34-51-79. E-mail address: [email protected] (S. Deprot).
the molten alloy to obtain a continuous metallic nucleus covered by an insulating glass coating. The starting alloys are the amorphous small negative magnetostrictive commercial 2705M alloy from VacuumSchmelze and alloys from the Co75:5x Fex Ni1.5B12Si11 system. We have chosen this alloy system in order to change the magnetostriction coefficient with the Fe/(Fe+Co) ratio. The Co75:5x Fex Ni1.5B12Si11 (x ¼ 2; 3 and 4 at%) master alloys were obtained by induction melting the appropriate amounts of Co, Fe, Ni, B, Si crystalline materials in the argon atmosphere. To ensure a good homogeneity of the alloys, several meltings were performed. The compositions of the produced microwires are presented in Table 1. By changing the casting parameters, the microwires were fabricated with different radii of the metallic nucleus and different thicknesses of the insulating coating. The diameter of the metallic core mainly depends on the winding speed and the drawing temperature. The higher the speed is, the smaller the diameter. The drawing temperature which determines the temperature–viscosity behaviour of the glass plays an important role. The X dependence on temperature drawing is presented in Fig. 1. X is the glass and metal cross-sectional ratio, X ¼ ðdw=dmÞ2 1; where dm is the metallic core diameter and dw the total diameter. As can be seen in Fig. 1, X increases considerably with the
0304-8853/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 1 ) 0 1 2 4 5 - 8
S. Deprot et al. / Journal of Magnetism and Magnetic Materials 242–245 (2002) 247–250
248
Table 1 Composition and magnetic properties of the investigated Co75:5x FexNi1.5B12Si11 microwires with dm ¼ 4 mm and dw ¼ 16 mm. Composition
Label
ls ( 106)
Ha (Oe)
Co71.5Fe4Ni1.5B12Si11 Co72.5Fe3Ni1.5B12Si11 Co 73.5Fe2Ni1.5B12Si11
a b c
1.29 2.08 2.88
43 55 86
650
40
550
Apparent Permeability
45 35
X
30 25 20 15 10 5 0 1200
1220
1240
1260
1280
1300
1320
Temperature (°C) Fig. 1. X dependence on temperature drawing, where X is the glass and metal cross-sectional ratio, X ¼ ðdw=dmÞ2 1:
melt temperature. The total diameter is kept constant (16 mm), whereas the metallic nucleus decreases from 10 to 2.5 mm when the melt temperature increases from 12101C to 13001C. This is attributed to the temperature– viscosity behaviour of the glass. An optical immersion microscope has been employed to check the dimensional characteristics of the wires. Static magnetic characterization was carried out using a vibrating sample magnetometer (VSM). The microwave parallel permeability of the wires was measured in the range 130 MHz–18 GHz. The experimental measurement method consists of winding the glass-coated microwire into a torus and measuring the permeability of the sample using a coaxial line [6]. The apparent permeability ma of the wire is then deduced from the permeability of the composite mjj using the following relation: mjj ¼ qma þ ð1 qÞmm ; where q is the ferromagnetic volume fraction in the sample and mm the permeability of the insulating cover and non-magnetic matrix. The apparent permeability can be described by the coupling of skin effect and of the gyromagnetic permeability. The gyromagnetic resopffiffiffiffiffiffiffiffiffiffiffi nance frequency ðm0 ¼ 1Þ is given by fr ¼ g Bs Ha ; where Bs is the saturation induction, Ha the anisotropy field and g the gyromagnetic ratio. It is not affected by skin effect.
t = 2 µm t = 6 µm
450 350 250 150
µ"
50 -50 0.1 -150
10 µ' Frequency (GHz)
Fig. 2. Apparent relative permeability versus frequency for microwires obtained from the 2705M alloy with the same diameter of the metallic core (4 mm) but two different glass thicknesses (t ¼ 2 and 6 mm).
3. Results and discussion The influence of the stress quenched in the ferromagnetic core due to the difference in thermal expansion coefficients between the metallic nucleus and the glass coating [7] is analyzed by considering microwires with different glass thicknesses. Fig. 2 shows the permeability versus frequency in the gigahertz range for two microwires with the same nucleus diameter (4 mm) but two different thicknesses of coating (2 and 6 mm). It is expected that a thicker coating would lead to larger stresses and to higher values of the induced anisotropy, thus increasing the gyromagnetic resonance frequency. Indeed, for the sample with smaller glass coating thickness, the resonance frequency is at 700 MHz. For the sample with thicker glass coating, the resonance frequency rises to 1 GHz. When the metallic core diameter varies while keeping the total diameter constant, both stress-induced anisotropy and skin effect act on the permeability of the microwire. Fig. 3 shows the permeability of three wires of the same composition with a total diameter equal to 16 mm and metallic core diameter varying from 2.5 to 10 mm. For the 2.5 mm core diameter, the permeability is nearly free of skin effect: m0 is constant up to the neighbouring resonance frequency, and the frequency at which m00 is maximum corresponds to the resonance frequency. When the metallic diameter increases, the
S. Deprot et al. / Journal of Magnetism and Magnetic Materials 242–245 (2002) 247–250
Apparent Permeability
500 400
dm=2.5 µm dm=4 µm dm=10 µm
300 200
µ"
100 0 0.1
1
10
-100 -200
µ' Frequency (GHz)
Fig. 3. Apparent relative permeability versus frequency for microwires obtained from 2705M alloy with the same total diameter (16 mm) but different metallic core diameters dm ¼ 2:5; 4 and 10 mm.
249
evaluated from a relation established in the literature [8]. The values are collected in Table 1. Static magnetic characterizations were performed applying a magnetic field along the wire axis: flat hysteresis loops, typical of an amorphous wire with a negative magnetostrictive coefficient and a magnetic structure with circumferential domains are obtained [9]. Saturation magnetization variation from x ¼ 4 to 2 at% does not exceed 10%, whereas the anisotropy field Ha deduced from the hysteresis loops has been found to vary from 43 to 86 Oe (see Table 1). As expected, a correlation between ls and Ha is observed. The gyromagnetic resonance frequency deduced from the microwave permeability increases from 1.9 GHz for alloy (a) to 2.8 GHz for alloy (c). This is consistent with a growing anisotropy field.
4. Conclusion 250 (a)
Apparent Permeability
200 150
(b)
100
(c) µ"
50 0 0.1 -50 -100
1
10 µ'
Frequency (GHz)
Fig. 4. Apparent relative permeability versus frequency for glass-coated microwires obtained from (a), (b) and (c) alloys with the same metallic diameter (4 mm) and the same total diameter (16 mm).
resonance frequency decreases since the stress-induced anisotropy decreases. Moreover, due to an increase of skin effect, the ‘‘plateau’’ of m0 disappears. The m00 peak is attenuated and the frequency at m00 maximun is different from the resonance frequency. As mentioned in the introduction, the composition of the metallic nucleus plays a fundamental role in the magnetic properties of the microwires. Fig. 4 shows the permeability versus frequency of three wires with compositions a, b and c as reported in Table 1. To allow a comparative study of the composition effect, the geometric characteristics of the wires are similar for the three wires. The metallic core has been chosen equal to 4 mm to limit skin effect. The total diameter is 16 mm. As the wires are obtained in the same experimental conditions, the stresses are considered to be the same for the three wires. The magnetostriction constant ls is
In this paper, we have shown that the microwave response of amorphous glass-coated ferromagnetic microwires can be controlled by the geometric characteristics and the wire composition. The stresses in the ferromagnetic nucleus of the wire depend on the glass to metal cross-sectional ratio. These stresses induce a magnetic anisotropy whose intensity is related to the magnetostriction coefficient of the alloy. We have studied both the influence of the dimensions and of the magnetostriction constant on the microwave magnetic properties of ferromagnetic microwires in the gigahertz frequency range. The stress-induced anisotropy allows us to change the gyromagnetic resonance frequency from 700 MHz to 2.8 GHz, offering the possibility to use these wires in a wide variety of applications. Moreover, the shape of the frequency response of the microwave permeability is modified by the skin effect if the metallic core diameter exceeds 4 mm. Thin metallic core diameter wires are therefore very interesting for the study of the gyromagnetic resonance in these materials.
Acknowledgements The authors are grateful to P. De Rango and D. Fruchart of the Laboratoire de Cristallographie, Grenoble, for providing the alloys.
References [1] A. Zhukov, J. Gonzalez, J.M. Blanco, M. Vazquez, V. Larin, J. Mater. Res. 15 (2000) 2107. [2] A.F. Cobeno, A. Zhukov, J.M. Blanco, V. Larin, J. Gonzalez, J. Mater. Res. 14 (1999) 3775. [3] H. Chiriac, T.A. Ovari, Gh. Pop, F. Barariu, Sensors Actuators A 59 (1997) 243.
250
S. Deprot et al. / Journal of Magnetism and Magnetic Materials 242–245 (2002) 247–250
[4] D. M!enard, A. Yelon, J. Appl. Phys. 88 (2000) 379. [5] G.F. Taylor, Phys. Rev. 24 (1924) 655. [6] P.-M. Jacquart, O. Acher, IEEE Trans. Microwave Theory Tech. 44 (1996) 2116. [7] S. Antonov, V.t. Borisov, O.V. Borisov, A.F. Prokoshin, N.A. Usov, J. Phys. D: Appl. Phys. 33 (2000) 1161.
[8] K. Aso, S. Uedaira, M. Hayakawa, K. Hotai, Y. Ochiai, K. Hayashi, Y. Makino, J. Magn. Magn. Mater. 31–34 (1983) 1546. [9] M. Vazquez, A.P. Zhukov, J. Magn. Magn. Mater. 160 (1996) 223.