- Email: [email protected]
High-frequency behavior of amorphous microwires and its applications
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 290–291 (2005) 1597–1600 www.elsevier.com/locate/jmmm
High-frequency behavior of amorphous microwires and its applications P. Marı´ na,, D. Cortinab, A. Hernandoa a Instituto de Magnetismo Aplicado, P.O. Box 155, 28230 Las Rozas, Spain Micromag 2000 S.L., Pasaje 24-26, Polı´gono Euro´polis, 28230 Las Rozas, Spain
b
Available online 9 December 2004
Abstract A magnetic microwire is a continuous filament of total diameter less than 100 mm consisting of an inner metallic magnetic nuclei covered by a glassy outer shell, usually obtained by Taylor’s technique, with interesting magnetic properties connected with its high axial magnetic anisotropy. Magnetic sensors based on microwires used, as operating principle, the strong connection between the composition and the uniaxial anisotropy through a magnetostriction constant such as the large Barkhausen effect, Mateucci effect and giant magneto-impedance effect. The study of the microwave properties is also very promising technologically. In the microwave region (approaching GHz range), the ferromagnetic resonance (FMR) occurs and it is connected with the spin precession of the magnetisation vector due to the effect of the high-frequency electromagnetic field applied such that the magnetic component is perpendicular to the magnetisation vector. The natural ferromagnetic resonance (NFMR) has been also observed. The frequency depends upon the value of magnetic anisotropy and it is characterised by the single well-distinguished line in the 2–10 GHz range. Tags detector based on the microwires FMR and a new kind of electromagnetic radiation absorbers based on the microwires NFMR have been developed. r 2004 Elsevier B.V. All rights reserved. PACS: 75.50 Kj; 75.30 Gw; 46.25 Hf; 76.50.+g; 78.70 Gq; 84.40 Xb Keywords: Amorphous systems—wires; Magnetic field—microwave; Resonance—ferromagnetic; Anisotropy—magnetoelastic; Bistability
1. Introduction Amorphous metallic materials take a prominent position among metallic materials due to their unique and favorable association of physical properties related to the absence of the long-range order. Glass-coated magnetic microwires are obtained by extracting through melt-spinning technique, based on Taylor’s classical method [1]. Two main factors [2] are responsible for the Corresponding author. Tel.: +34 91 300 7175; fax: +34 91 300 7176. E-mail address: [email protected] (P. Marı´ n).
microwire magnetic behavior, i.e., the metallic core microstructure and the ratio of the metallic core radius to the total radius of the microwire r ¼ Rm =R: The tiny dimensions and the outstanding magnetic behavior at low-, medium-, and high-frequency magnetic fields make them very useful for applications.
2. Experimental details Two kinds of amorphous microwires were prepared by Taylor’s technique, low magnetostrictive ones, with nominal composition (Fe0.03Co0.97)75B15Si10, total
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2004.11.255
ARTICLE IN PRESS P. Marı´n et al. / Journal of Magnetism and Magnetic Materials 290–291 (2005) 1597–1600
1598
Antennas
1.0
microwire Low frequency Power Supply
Helmholtz coils
Magnetization (a.u.)
Spectrum analyzer
0.5
0.0
-0.5
-1.0
High frequency generator (1.2 Ghz)
-450
Fig. 1. Schematic drawing of the experimental set-up for highfrequency measurements.
3. Experimental results and conclusions Hysteresis loop shape is strongly dependent on the composition of the metallic core. The high-frequency magnetic behavior is connected with low-frequency hysteresis loop. Fig. 2 shows a non-bistable, with high initial permeability hysteresis loop, corresponding to Co-rich amorphous microwire. The lower saturation field is 90 A/m. Fig. 3 shows hysteresis loops, corresponding to the Fe-rich microwire, as a function of rU The microwires with large and positive magnetostriction constant, ls ; show magnetic bistability associated with the Barkhau-
-150
0
150
300
450
Axial Magnetic Field (A/m) Fig. 2. Hysteresis loop for (Fe0.03Co0.97)75B15Si10 magnetic microwire.
60 4 Magnetization (e.m.u. (10 ))
diameter, D, of 25 mm and the ratio of the metallic core radius to the total radius of the microwire, r ¼ 0:5 and positive magnetostrictive with nominal composition Fe89Si3B1C3Mn4 and r between 0.2 and 0.6. Low-frequency (80 Hz) hysteresis loops, have been measured by a conventional induction method. A maximum magnetization field of 15 Oe has been longitudinally applied to 10 cm length magnetic microwire. High-frequency studies have been performed by two methods. Co-rich microwires have been characterized by means of experimental set-up shown in Fig. 1. Helmholtz coils are used to apply a maximum low-frequency bias field (between 242 and 1002 mHz) of 120 A/m. Magnetic microwire (10 cm length) is situated in the center. The high-frequency signal (1.2 GHz) generated by emission antenna modulated by microwire presence is detected by the reception antenna and processed by the spectrum analyzer. Silicon resin has been mixed with 40 g of 1 mm length Fe-rich microwires to prepare 50 50 0.5 cm3 sheets. They have been characterized in electromagnetic anechoic chamber using normal incidence radiation with frequencies between 5 and 20 GHz.
-300
(a)
40 (b)
20
(c)
0
(d)
-20 -40 -60 -1000
-500 0 500 Axial Magnetic Field (A/m)
1000
Fig. 3. Hysteresis loop for Fe89Si3B1C3Mn4 microwires with different ratio r ¼ Rm =R; r ¼ 0:2 (a); r ¼ 0:25 (b); r ¼ 0:28 (c); r ¼ 0:6 (d).
sen jump. A higher longitudinal anisotropy due to thinner inner core is associated with a higher anisotropy field, H k ; and lower remanence [3]. Technologically, the study of the microwave properties is very promising. In the microwave region (approaching to GHz range), the ferromagnetic resonance (FMR) occurs, accompanied by energy absorption at the resonance frequency. Using Kittel’s equation [4] for a plane, the resonance frequency, f r ; can be calculated by means of fr ¼
g pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ðH a þ 4pMÞðH a þ HÞ; 2p
(1)
where H a is the magnetoelastic anisotropy field depending on r; ls and internal stress, so ; M the magnetisation, g the gyromagnetic ratio and H the external applied
ARTICLE IN PRESS P. Marı´n et al. / Journal of Magnetism and Magnetic Materials 290–291 (2005) 1597–1600
frequency electromagnetic field applied such that the magnetic component is perpendicular to the magnetisation vector [5]. As rule, the observation of FMR needs application of an external DC, or very low-frequency magnetic field which provides uniform magnetization of examined sample. This effect has been studied by means of experimental set-up shown in Fig. 1 in non-bistable Co-rich microwire with corresponding hysteresis loop shown in Fig. 2. Fig. 4A shows the influence of bias field amplitude in signal modulation. Certain field with frequency of 528 mHz has been applied in order to magnetize the Co-rich microwire. The magnetic field amplitude decrease (from 120 to 20 A/m) is associated to a decrease in second antenna detected signal. The FMR frequency, associated to this microwire, has been detected to be 1.2 GHz. The electromagnetic wave absorption effect becomes less important when the bias field amplitude is below 90 A/m, the lower saturation field of this sample. Fig. 4B shows the influence of bias field frequency in signal modulation. This fact reveals how FMR needs the application of external magnetic field and how the effect is observed only in the case of saturated sample. So, when low-frequency but AC magnetic field goes to zero, no FMR is observed. One of the most interesting phenomena observed in amorphous ferromagnetic cast microwires is natural ferromagnetic resonance (NFMR) [6]. The NFMR was, first, observed in ferrites in the absence of an external magnetic field due to the presence of the internal magnetic anisotropy. The frequency depends upon the value of the magnetic anisotropy. Fig. 5 shows the absorption curves, obtained in the anechoic chamber, for silicon-microwire sheets prepared with the microwires associated to hysteresis loops shown in Fig. 3. The appearance of NFMR in positive magnetostrictive microwires indicates the existence of a large magnetic anisotropy. The magnetic component of the AC field (GHz) is perpendicular to the microwire
magnetic field. At that frequency, the permeability increases dramatically and the skin depth is very small (less than 1 mm). At a given frequency, f r ; and field, H, around the resonance, the increased magnetic biasing field, H a ; shifts the resonance frequency to a higher frequency. FMR is connected with spin precession about the magnetisation vector due to the effect of a high-
Absorption level (a.u.)
(a)
(b)
(c)
(d) Time (s)
(A)
Absorption level (a.u.)
(a)
(b)
(c) Time (s)
(B)
Fig. 4. (A) Influence of bias field amplitude for Co-rich microwires 1.2 GHz absorption level ((a) 22 A/m, (b) 36 A/m, (c) 60 A/m, (d) 120 A/m); (B) influence of bias field frequency for Co-rich microwire on 1.2 GHz signal absorption level ((a) 242 MHz, (b) 528 mHz, (c) 1001 mHz).
0 Absorption level dB
1599
a b c d
-5 -10 -15 8.2 GHz
-20
10.3 GHz
13.2 GHz
7.4 GHz
-25 5
6
7
8
9
10
11
12
13
14
15
16
17
18
Frecuency (GHz) Fig. 5. Absorption level versus wave frequency for electromagnetic absorbing sheets prepared using Fe89 Si3B1C3Mn4 microwires with different ratio r ¼ Rm =R; (a) r ¼ 0:2; (b) r ¼ 0:25; (c) r ¼ 0:28; (d) r ¼ 0:6:
ARTICLE IN PRESS 1600
P. Marı´n et al. / Journal of Magnetism and Magnetic Materials 290–291 (2005) 1597–1600
axis, so the internal magnetic anisotropy provides that the microwire is magnetized along its axis. This conclusion agrees well with the axial magnetization presented by bistable magnetic microwires. The calculation of the NFMR frequency may be done using Eq. (1) for plane, considering H ¼ 0: If H a 54pM; shows the strong dependence of resonance frequency with composition, trough magnetostriction constant, and fabrication conditions, through r and s0 [6]. Fig. 5 points out the dependence of the anisotropy field, H k ; and the NFMR on the ratio r ¼ Rm =R for Fe89Si3B1C3Mn4 microwires shown in Fig. 3.
4. Applications Magnetic tags based on FMR can be developed using microwires as sensing element. A detector system based on this effect allows the tag detection in big volumes compared with the conventional electromagnetic or
acustomagnetic systems based on amorphous ribbons. Radar absorbing material using NFMR of magnetic microwires can be developed presenting higher absorption levels and better oxidation and corrosion properties than those using ferrites [7].
References [1] G.F. Taylor, Phys. Rev. 24 (1924) 6555. [2] H. Chiriac, T.A. O´va´ri, Prog. Mater. Sci. 40 (1997) 333. [3] P. Marı´ n, A. Hernando, J. Magn. Magn. Mater. 215–216 (2000) 729. [4] C. Kittel, Phys. Rev. 73 (1948) 155. [5] A.N. Antonenko, S.A. Baranov, V.S. Larin, A.V. Torkunov, J. Mater. Sci. Eng. A 248 (1997) 248. [6] L. Kraus, Z. Frait, I. Schneider, Phys. Status Solidi A 63 (1981) 669. [7] D.M. Grimes, W.W. Raymond, R.J. Hach, R.M. Walser, US Patent 3.938.152 (1976).
Journal of Magnetism and Magnetic Materials 290–291 (2005) 1597–1600 www.elsevier.com/locate/jmmm
High-frequency behavior of amorphous microwires and its applications P. Marı´ na,, D. Cortinab, A. Hernandoa a Instituto de Magnetismo Aplicado, P.O. Box 155, 28230 Las Rozas, Spain Micromag 2000 S.L., Pasaje 24-26, Polı´gono Euro´polis, 28230 Las Rozas, Spain
b
Available online 9 December 2004
Abstract A magnetic microwire is a continuous filament of total diameter less than 100 mm consisting of an inner metallic magnetic nuclei covered by a glassy outer shell, usually obtained by Taylor’s technique, with interesting magnetic properties connected with its high axial magnetic anisotropy. Magnetic sensors based on microwires used, as operating principle, the strong connection between the composition and the uniaxial anisotropy through a magnetostriction constant such as the large Barkhausen effect, Mateucci effect and giant magneto-impedance effect. The study of the microwave properties is also very promising technologically. In the microwave region (approaching GHz range), the ferromagnetic resonance (FMR) occurs and it is connected with the spin precession of the magnetisation vector due to the effect of the high-frequency electromagnetic field applied such that the magnetic component is perpendicular to the magnetisation vector. The natural ferromagnetic resonance (NFMR) has been also observed. The frequency depends upon the value of magnetic anisotropy and it is characterised by the single well-distinguished line in the 2–10 GHz range. Tags detector based on the microwires FMR and a new kind of electromagnetic radiation absorbers based on the microwires NFMR have been developed. r 2004 Elsevier B.V. All rights reserved. PACS: 75.50 Kj; 75.30 Gw; 46.25 Hf; 76.50.+g; 78.70 Gq; 84.40 Xb Keywords: Amorphous systems—wires; Magnetic field—microwave; Resonance—ferromagnetic; Anisotropy—magnetoelastic; Bistability
1. Introduction Amorphous metallic materials take a prominent position among metallic materials due to their unique and favorable association of physical properties related to the absence of the long-range order. Glass-coated magnetic microwires are obtained by extracting through melt-spinning technique, based on Taylor’s classical method [1]. Two main factors [2] are responsible for the Corresponding author. Tel.: +34 91 300 7175; fax: +34 91 300 7176. E-mail address: [email protected] (P. Marı´ n).
microwire magnetic behavior, i.e., the metallic core microstructure and the ratio of the metallic core radius to the total radius of the microwire r ¼ Rm =R: The tiny dimensions and the outstanding magnetic behavior at low-, medium-, and high-frequency magnetic fields make them very useful for applications.
2. Experimental details Two kinds of amorphous microwires were prepared by Taylor’s technique, low magnetostrictive ones, with nominal composition (Fe0.03Co0.97)75B15Si10, total
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2004.11.255
ARTICLE IN PRESS P. Marı´n et al. / Journal of Magnetism and Magnetic Materials 290–291 (2005) 1597–1600
1598
Antennas
1.0
microwire Low frequency Power Supply
Helmholtz coils
Magnetization (a.u.)
Spectrum analyzer
0.5
0.0
-0.5
-1.0
High frequency generator (1.2 Ghz)
-450
Fig. 1. Schematic drawing of the experimental set-up for highfrequency measurements.
3. Experimental results and conclusions Hysteresis loop shape is strongly dependent on the composition of the metallic core. The high-frequency magnetic behavior is connected with low-frequency hysteresis loop. Fig. 2 shows a non-bistable, with high initial permeability hysteresis loop, corresponding to Co-rich amorphous microwire. The lower saturation field is 90 A/m. Fig. 3 shows hysteresis loops, corresponding to the Fe-rich microwire, as a function of rU The microwires with large and positive magnetostriction constant, ls ; show magnetic bistability associated with the Barkhau-
-150
0
150
300
450
Axial Magnetic Field (A/m) Fig. 2. Hysteresis loop for (Fe0.03Co0.97)75B15Si10 magnetic microwire.
60 4 Magnetization (e.m.u. (10 ))
diameter, D, of 25 mm and the ratio of the metallic core radius to the total radius of the microwire, r ¼ 0:5 and positive magnetostrictive with nominal composition Fe89Si3B1C3Mn4 and r between 0.2 and 0.6. Low-frequency (80 Hz) hysteresis loops, have been measured by a conventional induction method. A maximum magnetization field of 15 Oe has been longitudinally applied to 10 cm length magnetic microwire. High-frequency studies have been performed by two methods. Co-rich microwires have been characterized by means of experimental set-up shown in Fig. 1. Helmholtz coils are used to apply a maximum low-frequency bias field (between 242 and 1002 mHz) of 120 A/m. Magnetic microwire (10 cm length) is situated in the center. The high-frequency signal (1.2 GHz) generated by emission antenna modulated by microwire presence is detected by the reception antenna and processed by the spectrum analyzer. Silicon resin has been mixed with 40 g of 1 mm length Fe-rich microwires to prepare 50 50 0.5 cm3 sheets. They have been characterized in electromagnetic anechoic chamber using normal incidence radiation with frequencies between 5 and 20 GHz.
-300
(a)
40 (b)
20
(c)
0
(d)
-20 -40 -60 -1000
-500 0 500 Axial Magnetic Field (A/m)
1000
Fig. 3. Hysteresis loop for Fe89Si3B1C3Mn4 microwires with different ratio r ¼ Rm =R; r ¼ 0:2 (a); r ¼ 0:25 (b); r ¼ 0:28 (c); r ¼ 0:6 (d).
sen jump. A higher longitudinal anisotropy due to thinner inner core is associated with a higher anisotropy field, H k ; and lower remanence [3]. Technologically, the study of the microwave properties is very promising. In the microwave region (approaching to GHz range), the ferromagnetic resonance (FMR) occurs, accompanied by energy absorption at the resonance frequency. Using Kittel’s equation [4] for a plane, the resonance frequency, f r ; can be calculated by means of fr ¼
g pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ðH a þ 4pMÞðH a þ HÞ; 2p
(1)
where H a is the magnetoelastic anisotropy field depending on r; ls and internal stress, so ; M the magnetisation, g the gyromagnetic ratio and H the external applied
ARTICLE IN PRESS P. Marı´n et al. / Journal of Magnetism and Magnetic Materials 290–291 (2005) 1597–1600
frequency electromagnetic field applied such that the magnetic component is perpendicular to the magnetisation vector [5]. As rule, the observation of FMR needs application of an external DC, or very low-frequency magnetic field which provides uniform magnetization of examined sample. This effect has been studied by means of experimental set-up shown in Fig. 1 in non-bistable Co-rich microwire with corresponding hysteresis loop shown in Fig. 2. Fig. 4A shows the influence of bias field amplitude in signal modulation. Certain field with frequency of 528 mHz has been applied in order to magnetize the Co-rich microwire. The magnetic field amplitude decrease (from 120 to 20 A/m) is associated to a decrease in second antenna detected signal. The FMR frequency, associated to this microwire, has been detected to be 1.2 GHz. The electromagnetic wave absorption effect becomes less important when the bias field amplitude is below 90 A/m, the lower saturation field of this sample. Fig. 4B shows the influence of bias field frequency in signal modulation. This fact reveals how FMR needs the application of external magnetic field and how the effect is observed only in the case of saturated sample. So, when low-frequency but AC magnetic field goes to zero, no FMR is observed. One of the most interesting phenomena observed in amorphous ferromagnetic cast microwires is natural ferromagnetic resonance (NFMR) [6]. The NFMR was, first, observed in ferrites in the absence of an external magnetic field due to the presence of the internal magnetic anisotropy. The frequency depends upon the value of the magnetic anisotropy. Fig. 5 shows the absorption curves, obtained in the anechoic chamber, for silicon-microwire sheets prepared with the microwires associated to hysteresis loops shown in Fig. 3. The appearance of NFMR in positive magnetostrictive microwires indicates the existence of a large magnetic anisotropy. The magnetic component of the AC field (GHz) is perpendicular to the microwire
magnetic field. At that frequency, the permeability increases dramatically and the skin depth is very small (less than 1 mm). At a given frequency, f r ; and field, H, around the resonance, the increased magnetic biasing field, H a ; shifts the resonance frequency to a higher frequency. FMR is connected with spin precession about the magnetisation vector due to the effect of a high-
Absorption level (a.u.)
(a)
(b)
(c)
(d) Time (s)
(A)
Absorption level (a.u.)
(a)
(b)
(c) Time (s)
(B)
Fig. 4. (A) Influence of bias field amplitude for Co-rich microwires 1.2 GHz absorption level ((a) 22 A/m, (b) 36 A/m, (c) 60 A/m, (d) 120 A/m); (B) influence of bias field frequency for Co-rich microwire on 1.2 GHz signal absorption level ((a) 242 MHz, (b) 528 mHz, (c) 1001 mHz).
0 Absorption level dB
1599
a b c d
-5 -10 -15 8.2 GHz
-20
10.3 GHz
13.2 GHz
7.4 GHz
-25 5
6
7
8
9
10
11
12
13
14
15
16
17
18
Frecuency (GHz) Fig. 5. Absorption level versus wave frequency for electromagnetic absorbing sheets prepared using Fe89 Si3B1C3Mn4 microwires with different ratio r ¼ Rm =R; (a) r ¼ 0:2; (b) r ¼ 0:25; (c) r ¼ 0:28; (d) r ¼ 0:6:
ARTICLE IN PRESS 1600
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axis, so the internal magnetic anisotropy provides that the microwire is magnetized along its axis. This conclusion agrees well with the axial magnetization presented by bistable magnetic microwires. The calculation of the NFMR frequency may be done using Eq. (1) for plane, considering H ¼ 0: If H a 54pM; shows the strong dependence of resonance frequency with composition, trough magnetostriction constant, and fabrication conditions, through r and s0 [6]. Fig. 5 points out the dependence of the anisotropy field, H k ; and the NFMR on the ratio r ¼ Rm =R for Fe89Si3B1C3Mn4 microwires shown in Fig. 3.
4. Applications Magnetic tags based on FMR can be developed using microwires as sensing element. A detector system based on this effect allows the tag detection in big volumes compared with the conventional electromagnetic or
acustomagnetic systems based on amorphous ribbons. Radar absorbing material using NFMR of magnetic microwires can be developed presenting higher absorption levels and better oxidation and corrosion properties than those using ferrites [7].
References [1] G.F. Taylor, Phys. Rev. 24 (1924) 6555. [2] H. Chiriac, T.A. O´va´ri, Prog. Mater. Sci. 40 (1997) 333. [3] P. Marı´ n, A. Hernando, J. Magn. Magn. Mater. 215–216 (2000) 729. [4] C. Kittel, Phys. Rev. 73 (1948) 155. [5] A.N. Antonenko, S.A. Baranov, V.S. Larin, A.V. Torkunov, J. Mater. Sci. Eng. A 248 (1997) 248. [6] L. Kraus, Z. Frait, I. Schneider, Phys. Status Solidi A 63 (1981) 669. [7] D.M. Grimes, W.W. Raymond, R.J. Hach, R.M. Walser, US Patent 3.938.152 (1976).