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Surface magnetic properties of Co69Fe4Si15B12 when DC and AC currents flow through the ribbon
Journal of Magnetism and Magnetic Materials 304 (2006) e853–e855 www.elsevier.com/locate/jmmm
Surface magnetic properties of Co69Fe4Si15B12 when DC and AC currents flow through the ribbon Vanessa Fal-Miyara, Galina V. Kurlyandskayab, Jose A. Garcı´ aa, Laura Elbailea,, Rosario D. Crespoa, Marcos Tejedora a Departamento de Fı´sica. Universidad de Oviedo, c/ Calvo Sotelo s.n.,33007, Oviedo, Spain Universidad del Paı´s Vasco UPV-EHU, Dpto. Electricidad y Electro´nica, Apdo. 644, 48080, Bilbao, Spain
b
Available online 27 March 2006
Abstract Surface magnetic properties of Co69 Fe4 Si15 B12 amorphous ribbons with longitudinal and transverse anisotropies when an electrical current flows through the ribbons has been studied. Observations were performed by the transverse magnetooptical Kerr effect. A DC electrical current caused a shift of the transverse hysteresis loop and AC current produced an increase of the coercive field. r 2006 Elsevier B.V. All rights reserved. PACS: 75.70.i; 77.80.Dj; 75.30.Gw Keywords: Amorphous ribbons; Anisotropy; Kerr effect; Giant magnetoimpedance
1. Introduction Amorphous magnetic ribbons are widely used in sensor technology. Different magnetic effects were proposed recently for biosensing: the Hall effect, magnetoresistance (MR), magnetoimpedance (MI) and nanomagnet dynamics in gigahertz scale [1,2]. Amorphous magnetic ribbons showing giant MI effect are candidates to be employed as a sensitive magnetic element for biosensors because they can present both, very high sensitivity with respect to magnetic field [3] and stability in aggressive environment. Recently, a giant MI biosensor prototype based on amorphous ribbon was tested in combination with commercial Dynabeadss -480 used as magnetic marker [1]. The detection was based on sensing of very weak magnetic fields created by the magnetic markers near the surface of the magnetic sensitive element. Therefore the surface properties are fundamental in order to obtain an optimum combination of the sensor nuclei material and the magnetic marker for the best performance. Corresponding author. Tel.: +11 34 985 103308; fax: +11 34 985 103324. E-mail address: [email protected] (L. Elbaile).
0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.03.016
A lot of work has been devoted to tailor the magnetic properties of amorphous ribbons. The improvement of their magnetic behaviour can be obtained by thermal treatments, but this often cause an unwanted enbrittlement of the materials. Recently, magnetic anisotropies have been induced in amorphous magnetic ribbons by applying a magnetic field during the solidification process (field quenching technique) avoiding the deterioration of their mechanical properties [4]. The surface magnetic properties of soft magnetic materials can be studied by magnetooptical Kerr effect (MOKE) [5,6]. In this work, we present the study of the surface magnetic properties and the magnetic domain structure of Co69 Fe4 Si15 B12 amorphous ribbons fabricated with or without application of the magnetic field during the solidification process and showing giant MI effect. 2. Experimental setup Amorphous ribbons of Co69 Fe4 Si15 B12 were prepared by the single roller melt spinning technique. Two sets of samples were produced in close conditions: one without application of a magnetic field during solidification (type A) and another one with a magnetic field of 0.07 T applied
V. Fal-Miyar et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e853–e855
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e854
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(a)
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-0.5 -1 -100
100
H(Am-1)
0
(b)
-50
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50
100
H(Am-1)
Fig. 1. Longitudinal hysteresis loops by MOKE of the ribbon for the sample A (a) and B (b).
in the transverse direction during solidification (type B). Samples of 60 mm length, 1 mm width and 25 mm thick were measured. The domain structure has been studied in remanence state by Bitter technique using a commercial EMG 507 ferrofluid. For some observations a very small magnetic field perpendicular to the ribbon surface was applied in order to polarize the ferrofluid. The MI effect was measured by standard four point technique in frequency range of 0.5–10 MHz for the driving currents of 5–25 mA in external magnetic field up to 140 Oe. The MI ratio was defined as follows: DðHÞ ZðH ¼ 140 OeÞ ZðHÞ ¼ 100 . ZðHÞ ZðH ¼ 140 OeÞ
(1)
The surface hysteresis loops have been measured using a transverse MOKE. The incoming light needs to be polarized parallel to the plane of incidence (p-polarized). In this case the reflected intensity is modulated by the magnetization component parallel to the sample surface and perpendicular to the plane of incidence. In order to analyse the transverse magnetization behaviour in the conditions close to those which appear during the biosensing process, the MOKE curves were measured when an electrical current flowed along the ribbon. The same transversal configuration of the MOKE was used but with the incidence plane perpendicular to the transverse component of the magnetization. The intensity of the DC electrical current was 25 mA and the same intensity with a frequency of 1 MHz was employed in the AC case. 3. Results and discussion The two sets of samples had the same composition analyses by XPDF technique. The amorphous state of the ribbons has been checked by X-ray diffraction. Fig. 1 shows the longitudinal hysteresis loops obtained by MOKE in A and B type ribbons. Hysteresis loop of the as-quenched ribbon (Fig. 1(a)) indicates that the effective anisotropy is close to longitudinal. Slight deviation of the easiest magnetization axis from the axis of the ribbon is not surprising for as-quenched ribbons. The hysteresis loop in Fig. 1(b) resembles the expected one from a transverse anisotropy.
Fig. 2. Magnetic domain structure observed by Bitter technique in sample B. Observation area is 0:5 0:78 mm. The axis of the ribbon is close to the longitudinal direction.
Both A and B samples had shown rather high MI value. The maximum of the MI ratio of about 95% for A and 120% for B ribbons was measured for the frequency of 5 MHz and driving current intensity of 25 mA. It was not possible to observe the principal domain structure in type A ribbons. But the closure domains near the surface defects were indicating the presence of longitudinal anisotropy. The magnetic domains of type B ribbons are shown in Fig. 2. The most important feature is the presence of knife-like, more or less equidistant closure domains, oriented perpendicular to the axis of the ribbon. The magnetization in these domains is most probably transverse to the ribbon axis. The observed domain patterns can be considered as an additional confirmation of the existence of transverse magnetic anisotropy on the surface field-quenched ribbons. The transverse hysteresis loops of sample B measured with the electrical current flowing through the ribbons are shown in Fig 3. Similar hysteresis loops have been observed in Co67 Fe3:85 Ni1:45 B11:5 Si14:5 Mo1:7 glass-covered amorphous microwires [6] and they can be explained in the following way. In the case of the hysteresis loops in the absence of electric current when the longitudinal magnetic field decreases from 96:8 A m1 there is a monotonic increase of the Kerr signal. This increase would be due to the rotation of the magnetization from the longitudinal to the transverse direction. Then, there is a decrease of the
1
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0.5
M / MS
M / MS
V. Fal-Miyar et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e853–e855
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e855
-50
0
50
-1 -100
100
H(Am-1)
(b)
-50
0
50
100
H(Am-1)
Fig. 3. Transverse hysteresis loops of the sample B (a) I ¼ 0, (b) I AC ¼ 25 m A and f ¼ 1 MHz.
Kerr signal which could be related to the nucleation of domains with the magnetization oriented in the direction of the easy axis of anisotropy i.e. transverse domain. With a DC current applied the transverse hysteresis loop is shifted. This shift is originated by the superimposed transverse magnetic field caused by the electrical current. When the high-frequency electric currents (1 MHz) of 25 mA flow through the ribbon, an increase of the coercive field from 3 to 5 A m1 can be observed in Fig. 3(b). This behaviour can be explained by a disaccommodation effect, since the high-frequency electric current invokes oscillations of domain walls which have a specific effective mass. Acknowledgments We thank Dr. A. Saad for her assistance. This work was supported in part by the Comision Interministerial de
Ciencia y Tecnologia of the Spanish Government under Grant no. MAT-2003-06407, and Ramon y Cajal Fellowship of Spanish MEC.
References [1] G.V. Kurlyandskaya, V.I. Levit, Biosen. and Bioelect. 20 (2005) 1611. [2] M. Megens, M. Prins, J. Magn. Magn. Mater. 293 (2005) 702. [3] K. Mohri, T. Uchiyama, L.V. Panina, Sensors Actuators A 59 (1997) 1. [4] M. Tejedor, J.A. Garcia, J. Carrizo, L. Elbaile, J.D. Santos, Appl. Phys. Lett. 82 (2003) 937. [5] I. Orue, A. Garcia-Arribas, A. Saad, D. de Cos, J.M. Bariandaran, J. Magn. Magn. Mater. 290–291 (2005) 1081. [6] A. Chizhik, A. Zhukov, J. Gonzalez, J.M. Blanco, J. Appl. Phys. 97(1–6) 073912.
Surface magnetic properties of Co69Fe4Si15B12 when DC and AC currents flow through the ribbon Vanessa Fal-Miyara, Galina V. Kurlyandskayab, Jose A. Garcı´ aa, Laura Elbailea,, Rosario D. Crespoa, Marcos Tejedora a Departamento de Fı´sica. Universidad de Oviedo, c/ Calvo Sotelo s.n.,33007, Oviedo, Spain Universidad del Paı´s Vasco UPV-EHU, Dpto. Electricidad y Electro´nica, Apdo. 644, 48080, Bilbao, Spain
b
Available online 27 March 2006
Abstract Surface magnetic properties of Co69 Fe4 Si15 B12 amorphous ribbons with longitudinal and transverse anisotropies when an electrical current flows through the ribbons has been studied. Observations were performed by the transverse magnetooptical Kerr effect. A DC electrical current caused a shift of the transverse hysteresis loop and AC current produced an increase of the coercive field. r 2006 Elsevier B.V. All rights reserved. PACS: 75.70.i; 77.80.Dj; 75.30.Gw Keywords: Amorphous ribbons; Anisotropy; Kerr effect; Giant magnetoimpedance
1. Introduction Amorphous magnetic ribbons are widely used in sensor technology. Different magnetic effects were proposed recently for biosensing: the Hall effect, magnetoresistance (MR), magnetoimpedance (MI) and nanomagnet dynamics in gigahertz scale [1,2]. Amorphous magnetic ribbons showing giant MI effect are candidates to be employed as a sensitive magnetic element for biosensors because they can present both, very high sensitivity with respect to magnetic field [3] and stability in aggressive environment. Recently, a giant MI biosensor prototype based on amorphous ribbon was tested in combination with commercial Dynabeadss -480 used as magnetic marker [1]. The detection was based on sensing of very weak magnetic fields created by the magnetic markers near the surface of the magnetic sensitive element. Therefore the surface properties are fundamental in order to obtain an optimum combination of the sensor nuclei material and the magnetic marker for the best performance. Corresponding author. Tel.: +11 34 985 103308; fax: +11 34 985 103324. E-mail address: [email protected] (L. Elbaile).
0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2006.03.016
A lot of work has been devoted to tailor the magnetic properties of amorphous ribbons. The improvement of their magnetic behaviour can be obtained by thermal treatments, but this often cause an unwanted enbrittlement of the materials. Recently, magnetic anisotropies have been induced in amorphous magnetic ribbons by applying a magnetic field during the solidification process (field quenching technique) avoiding the deterioration of their mechanical properties [4]. The surface magnetic properties of soft magnetic materials can be studied by magnetooptical Kerr effect (MOKE) [5,6]. In this work, we present the study of the surface magnetic properties and the magnetic domain structure of Co69 Fe4 Si15 B12 amorphous ribbons fabricated with or without application of the magnetic field during the solidification process and showing giant MI effect. 2. Experimental setup Amorphous ribbons of Co69 Fe4 Si15 B12 were prepared by the single roller melt spinning technique. Two sets of samples were produced in close conditions: one without application of a magnetic field during solidification (type A) and another one with a magnetic field of 0.07 T applied
V. Fal-Miyar et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e853–e855
1
1
0.5
0.5
M / MS
M / MS
e854
0 -0.5 -1 -100
-50
(a)
0
50
-0.5 -1 -100
100
H(Am-1)
0
(b)
-50
0
50
100
H(Am-1)
Fig. 1. Longitudinal hysteresis loops by MOKE of the ribbon for the sample A (a) and B (b).
in the transverse direction during solidification (type B). Samples of 60 mm length, 1 mm width and 25 mm thick were measured. The domain structure has been studied in remanence state by Bitter technique using a commercial EMG 507 ferrofluid. For some observations a very small magnetic field perpendicular to the ribbon surface was applied in order to polarize the ferrofluid. The MI effect was measured by standard four point technique in frequency range of 0.5–10 MHz for the driving currents of 5–25 mA in external magnetic field up to 140 Oe. The MI ratio was defined as follows: DðHÞ ZðH ¼ 140 OeÞ ZðHÞ ¼ 100 . ZðHÞ ZðH ¼ 140 OeÞ
(1)
The surface hysteresis loops have been measured using a transverse MOKE. The incoming light needs to be polarized parallel to the plane of incidence (p-polarized). In this case the reflected intensity is modulated by the magnetization component parallel to the sample surface and perpendicular to the plane of incidence. In order to analyse the transverse magnetization behaviour in the conditions close to those which appear during the biosensing process, the MOKE curves were measured when an electrical current flowed along the ribbon. The same transversal configuration of the MOKE was used but with the incidence plane perpendicular to the transverse component of the magnetization. The intensity of the DC electrical current was 25 mA and the same intensity with a frequency of 1 MHz was employed in the AC case. 3. Results and discussion The two sets of samples had the same composition analyses by XPDF technique. The amorphous state of the ribbons has been checked by X-ray diffraction. Fig. 1 shows the longitudinal hysteresis loops obtained by MOKE in A and B type ribbons. Hysteresis loop of the as-quenched ribbon (Fig. 1(a)) indicates that the effective anisotropy is close to longitudinal. Slight deviation of the easiest magnetization axis from the axis of the ribbon is not surprising for as-quenched ribbons. The hysteresis loop in Fig. 1(b) resembles the expected one from a transverse anisotropy.
Fig. 2. Magnetic domain structure observed by Bitter technique in sample B. Observation area is 0:5 0:78 mm. The axis of the ribbon is close to the longitudinal direction.
Both A and B samples had shown rather high MI value. The maximum of the MI ratio of about 95% for A and 120% for B ribbons was measured for the frequency of 5 MHz and driving current intensity of 25 mA. It was not possible to observe the principal domain structure in type A ribbons. But the closure domains near the surface defects were indicating the presence of longitudinal anisotropy. The magnetic domains of type B ribbons are shown in Fig. 2. The most important feature is the presence of knife-like, more or less equidistant closure domains, oriented perpendicular to the axis of the ribbon. The magnetization in these domains is most probably transverse to the ribbon axis. The observed domain patterns can be considered as an additional confirmation of the existence of transverse magnetic anisotropy on the surface field-quenched ribbons. The transverse hysteresis loops of sample B measured with the electrical current flowing through the ribbons are shown in Fig 3. Similar hysteresis loops have been observed in Co67 Fe3:85 Ni1:45 B11:5 Si14:5 Mo1:7 glass-covered amorphous microwires [6] and they can be explained in the following way. In the case of the hysteresis loops in the absence of electric current when the longitudinal magnetic field decreases from 96:8 A m1 there is a monotonic increase of the Kerr signal. This increase would be due to the rotation of the magnetization from the longitudinal to the transverse direction. Then, there is a decrease of the
1
1
0.5
0.5
M / MS
M / MS
V. Fal-Miyar et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e853–e855
0
(a)
0 -0.5
-0.5 -1 -100
e855
-50
0
50
-1 -100
100
H(Am-1)
(b)
-50
0
50
100
H(Am-1)
Fig. 3. Transverse hysteresis loops of the sample B (a) I ¼ 0, (b) I AC ¼ 25 m A and f ¼ 1 MHz.
Kerr signal which could be related to the nucleation of domains with the magnetization oriented in the direction of the easy axis of anisotropy i.e. transverse domain. With a DC current applied the transverse hysteresis loop is shifted. This shift is originated by the superimposed transverse magnetic field caused by the electrical current. When the high-frequency electric currents (1 MHz) of 25 mA flow through the ribbon, an increase of the coercive field from 3 to 5 A m1 can be observed in Fig. 3(b). This behaviour can be explained by a disaccommodation effect, since the high-frequency electric current invokes oscillations of domain walls which have a specific effective mass. Acknowledgments We thank Dr. A. Saad for her assistance. This work was supported in part by the Comision Interministerial de
Ciencia y Tecnologia of the Spanish Government under Grant no. MAT-2003-06407, and Ramon y Cajal Fellowship of Spanish MEC.
References [1] G.V. Kurlyandskaya, V.I. Levit, Biosen. and Bioelect. 20 (2005) 1611. [2] M. Megens, M. Prins, J. Magn. Magn. Mater. 293 (2005) 702. [3] K. Mohri, T. Uchiyama, L.V. Panina, Sensors Actuators A 59 (1997) 1. [4] M. Tejedor, J.A. Garcia, J. Carrizo, L. Elbaile, J.D. Santos, Appl. Phys. Lett. 82 (2003) 937. [5] I. Orue, A. Garcia-Arribas, A. Saad, D. de Cos, J.M. Bariandaran, J. Magn. Magn. Mater. 290–291 (2005) 1081. [6] A. Chizhik, A. Zhukov, J. Gonzalez, J.M. Blanco, J. Appl. Phys. 97(1–6) 073912.