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The influence of the composition on the GMI effect in low magnetostrictive amorphous microwires
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 272–276 (2004) 1860–1861
The influence of the composition on the GMI effect in low magnetostrictive amorphous microwires Horia Chiriac1, Iulian Murgulescu, Nicoleta Lupu* National Institute of Research and Development for Technical Physics, 47 Mangeron Blvd, Iasi 700050, Romania
Abstract The influence of the composition on both the magnetostriction and the GMI effect in Co72.5xFexSi12.5B15 (x ¼ 5:526:2) amorphous glass-covered wires is investigated. The basic magnetic properties of these materials as well as internal stresses induced by the glass cover during the preparation process strongly influence the GMI effect. r 2004 Elsevier B.V. All rights reserved. PACS: 75.50.Kj Keywords: GMI effect; Amorphous glass-covered wires; Low magnetostrictive alloys
1. Introduction
2. Experimental procedure
GMI effect in low magnetostrictive amorphous wires is mainly influenced by two factors: the specific circumferential magnetic domain structure and dynamic magnetization processes [1]. The glass cover induces an additional anisotropy, which strongly influences the magnitude of the GMI effect in low magnetostrictive amorphous glass-covered wires [2]. From the point of view of sensing applications, the amorphous glass-covered wires are often preferred against the conventional amorphous wires due to their more reduced dimensions, i.e. the diameter of the metallic core varies from a few micrometers to a few tens of micrometers [3,4]. The aim of this paper is to present our recent results on the influence of the composition on both the sign of the saturation magnetostriction constant and the GMI effect in Co72.5xFexSi12.5B15 (x ¼ 5:526:2) amorphous glass-covered wires.
Amorphous glass-covered wires (AGCW) with nominal compositions Co72.5xFexSi12.5B15 (x ¼ 5:5; 5.8, 5.9, 5.95, 6.0, 6.2) were prepared by glass-coated melt spinning method at the National Institute of Research and Development for Technical Physics of Iasi, Romania [4]. The saturation magnetostriction constant (ls ) is changing the sign from negative (ls ¼ 0:23 106 for x ¼ 5:5 at% Fe) to small positive (ls ¼ þ0:05 106 for x ¼ 6:2 at% Fe) values when the Fe content increases, passing through zero for xB6:0: GMI measurements were performed in the high frequency range (100 kHz–10 MHz) for a driving AC current with the maximum value of 5 mA using a digital oscilloscope coupled with a computer, which allowed automatic frequency control, data acquisition, and processing. For comparison, we carried out GMI measurements on amorphous glass-covered wires having different compositions and saturation magnetostriction constants, with metallic core diameter of 30 mm and the glass cover thickness of 7 mm.
*Corresponding author. Tel.: +40-232-130680; fax: +40232-231132. E-mail addresses: [email protected] (H. Chiriac), [email protected] (N. Lupu). 1 Also to be corresponded to.
3. Results and discussion The axial dc field dependences of the impedance for f ¼ 0:1; 1, 5 and 10 MHz for Co72.5xFexSi12.5B15 (x ¼ 5:5;
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.541
ARTICLE IN PRESS H. Chiriac et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 1860–1861 120
60
f = 1MHz x = 5.5 at. % x = 5.95 at.% x = 6.0 at. % x = 6.2 at. %
50
40
Impedance (Ω)
Impedance (Ω)
f = 0.1 MHz
40
30
0 200 f = 5MHz
x = 5.5 at. % x = 5.95 at.% x = 6.0 at. % x = 6.2 at. %
f = 10 MHz 160 Impedance (Ω)
160 120 80
x = 5.5 at. % x = 5.95 at.% x = 6.0 at. % x = 6.2 at. %
80
240 200
Impedance (Ω)
1861
120
80 x = 5.5 at. % x = 5.95 at.% x = 6.0 at. % x = 6.2 at. %
40
40 0
0 -2000
-1000
0
1000
2000
-2000
-1000
0
1000
2000
Applied Field (A/m)
Applied Field (A/m)
Fig. 1. GMI curves for AGCW with different compositions and saturation magnetostriction constants measured at 100 kHz, 1 MHz, 5 MHz, and 10 MHz.
5.95, 6.0, 6.2) AGCW are illustrated in Fig. 1. It is to be noted that the GMI curves exhibit just one central peak for positive magnetostrictive AGCW with a Fe content of 6.2 at%, independent of the frequency. This behavior is related to the non-formation of the circumferential magnetic domain structure in the positive magnetostrictive glasscovered amorphous wires [5]. The impedance shows two maxima whose positions are changing to high DC fields with the frequency increase, for negative magnetostrictive AGCW (xo6). This displacement is mainly caused by the supplementary-induced anisotropy as the effect of the negative magnetostriction constant. For nearly zero magnetostrictive composition (x ¼ 6) the GMI behavior is very sensitive to the AC field frequency. Whereas at frequencies below 5 MHz the GMI presents just the central maximum, the increase of the frequency over 5 MHz results in the appearance of two maxima on the impedance curve, symmetrically disposed to zero field value. The maximum positions correspond to the anisotropy field, Hk : It is worthwhile to note that the best response of the GMI effect is obtained for x ¼ 5:95 and frequencies over 1 MHz. This different behavior, which is strongly
dependent on the saturation magnetostriction constant value, is caused by the variation of the penetration depth of the AC current, i.e. the magnetic domain structure and the existence or non-existence of the closure surface magnetic domains [6]. Thus, the GMI effect, which is very important for AGCW sensing applications, is very sensitive to the samples magnetostriction, i.e. composition, and the geometry of the samples.
References [1] L.V. Panina, K. Mohri, K. Bushida, M. Noda, J. Appl. Phys. 76 (1994) 6198. ! ari, C.-S. Marinescu, IEEE Trans. [2] H. Chiriac, T.-A. Ov! Magn. 33 (1997) 3352. [3] F.B. Humphrey, Mater. Sci. Eng. A179/A180 (1994) 66. ! ari, Prog. Mater. Sci. 40 (1996) 333. [4] H. Chiriac, T.-A. Ov! [5] K.R. Pirota, L. Kraus, H. Chiriac, M. Knobel, J. Magn. Magn. Mater. 226–230 (2001) 730. ! ari, IEEE Trans. Magn. 38 (2002) 3057. [6] H. Chiriac, T.-A. Ov!
Journal of Magnetism and Magnetic Materials 272–276 (2004) 1860–1861
The influence of the composition on the GMI effect in low magnetostrictive amorphous microwires Horia Chiriac1, Iulian Murgulescu, Nicoleta Lupu* National Institute of Research and Development for Technical Physics, 47 Mangeron Blvd, Iasi 700050, Romania
Abstract The influence of the composition on both the magnetostriction and the GMI effect in Co72.5xFexSi12.5B15 (x ¼ 5:526:2) amorphous glass-covered wires is investigated. The basic magnetic properties of these materials as well as internal stresses induced by the glass cover during the preparation process strongly influence the GMI effect. r 2004 Elsevier B.V. All rights reserved. PACS: 75.50.Kj Keywords: GMI effect; Amorphous glass-covered wires; Low magnetostrictive alloys
1. Introduction
2. Experimental procedure
GMI effect in low magnetostrictive amorphous wires is mainly influenced by two factors: the specific circumferential magnetic domain structure and dynamic magnetization processes [1]. The glass cover induces an additional anisotropy, which strongly influences the magnitude of the GMI effect in low magnetostrictive amorphous glass-covered wires [2]. From the point of view of sensing applications, the amorphous glass-covered wires are often preferred against the conventional amorphous wires due to their more reduced dimensions, i.e. the diameter of the metallic core varies from a few micrometers to a few tens of micrometers [3,4]. The aim of this paper is to present our recent results on the influence of the composition on both the sign of the saturation magnetostriction constant and the GMI effect in Co72.5xFexSi12.5B15 (x ¼ 5:526:2) amorphous glass-covered wires.
Amorphous glass-covered wires (AGCW) with nominal compositions Co72.5xFexSi12.5B15 (x ¼ 5:5; 5.8, 5.9, 5.95, 6.0, 6.2) were prepared by glass-coated melt spinning method at the National Institute of Research and Development for Technical Physics of Iasi, Romania [4]. The saturation magnetostriction constant (ls ) is changing the sign from negative (ls ¼ 0:23 106 for x ¼ 5:5 at% Fe) to small positive (ls ¼ þ0:05 106 for x ¼ 6:2 at% Fe) values when the Fe content increases, passing through zero for xB6:0: GMI measurements were performed in the high frequency range (100 kHz–10 MHz) for a driving AC current with the maximum value of 5 mA using a digital oscilloscope coupled with a computer, which allowed automatic frequency control, data acquisition, and processing. For comparison, we carried out GMI measurements on amorphous glass-covered wires having different compositions and saturation magnetostriction constants, with metallic core diameter of 30 mm and the glass cover thickness of 7 mm.
*Corresponding author. Tel.: +40-232-130680; fax: +40232-231132. E-mail addresses: [email protected] (H. Chiriac), [email protected] (N. Lupu). 1 Also to be corresponded to.
3. Results and discussion The axial dc field dependences of the impedance for f ¼ 0:1; 1, 5 and 10 MHz for Co72.5xFexSi12.5B15 (x ¼ 5:5;
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.541
ARTICLE IN PRESS H. Chiriac et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 1860–1861 120
60
f = 1MHz x = 5.5 at. % x = 5.95 at.% x = 6.0 at. % x = 6.2 at. %
50
40
Impedance (Ω)
Impedance (Ω)
f = 0.1 MHz
40
30
0 200 f = 5MHz
x = 5.5 at. % x = 5.95 at.% x = 6.0 at. % x = 6.2 at. %
f = 10 MHz 160 Impedance (Ω)
160 120 80
x = 5.5 at. % x = 5.95 at.% x = 6.0 at. % x = 6.2 at. %
80
240 200
Impedance (Ω)
1861
120
80 x = 5.5 at. % x = 5.95 at.% x = 6.0 at. % x = 6.2 at. %
40
40 0
0 -2000
-1000
0
1000
2000
-2000
-1000
0
1000
2000
Applied Field (A/m)
Applied Field (A/m)
Fig. 1. GMI curves for AGCW with different compositions and saturation magnetostriction constants measured at 100 kHz, 1 MHz, 5 MHz, and 10 MHz.
5.95, 6.0, 6.2) AGCW are illustrated in Fig. 1. It is to be noted that the GMI curves exhibit just one central peak for positive magnetostrictive AGCW with a Fe content of 6.2 at%, independent of the frequency. This behavior is related to the non-formation of the circumferential magnetic domain structure in the positive magnetostrictive glasscovered amorphous wires [5]. The impedance shows two maxima whose positions are changing to high DC fields with the frequency increase, for negative magnetostrictive AGCW (xo6). This displacement is mainly caused by the supplementary-induced anisotropy as the effect of the negative magnetostriction constant. For nearly zero magnetostrictive composition (x ¼ 6) the GMI behavior is very sensitive to the AC field frequency. Whereas at frequencies below 5 MHz the GMI presents just the central maximum, the increase of the frequency over 5 MHz results in the appearance of two maxima on the impedance curve, symmetrically disposed to zero field value. The maximum positions correspond to the anisotropy field, Hk : It is worthwhile to note that the best response of the GMI effect is obtained for x ¼ 5:95 and frequencies over 1 MHz. This different behavior, which is strongly
dependent on the saturation magnetostriction constant value, is caused by the variation of the penetration depth of the AC current, i.e. the magnetic domain structure and the existence or non-existence of the closure surface magnetic domains [6]. Thus, the GMI effect, which is very important for AGCW sensing applications, is very sensitive to the samples magnetostriction, i.e. composition, and the geometry of the samples.
References [1] L.V. Panina, K. Mohri, K. Bushida, M. Noda, J. Appl. Phys. 76 (1994) 6198. ! ari, C.-S. Marinescu, IEEE Trans. [2] H. Chiriac, T.-A. Ov! Magn. 33 (1997) 3352. [3] F.B. Humphrey, Mater. Sci. Eng. A179/A180 (1994) 66. ! ari, Prog. Mater. Sci. 40 (1996) 333. [4] H. Chiriac, T.-A. Ov! [5] K.R. Pirota, L. Kraus, H. Chiriac, M. Knobel, J. Magn. Magn. Mater. 226–230 (2001) 730. ! ari, IEEE Trans. Magn. 38 (2002) 3057. [6] H. Chiriac, T.-A. Ov!