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Investigation of magnetic structure in cold-drawn Fe-rich amorphous wire
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 279 (2004) 359–362
Investigation of magnetic structure in cold-drawn Fe-rich amorphous wire A. Chizhika,*, C. Garciaa, J. Gonzaleza, J.M. Blancob ! 20080, Spain Departamento F!ısica de Materiales, Facultad de Qu!ımica, UPV, 1072, San Sebastian ! 20018, Spain Departamento F!ısica Aplicada I, EUPDS, UPV/EHU, Plaza Europa, 1, San Sebastian
a b
Received 26 November 2003; received in revised form 26 January 2004
Abstract Magnetic properties of Fe-rich amorphous wires, prepared by in-rotating-water-quenching technique and submitted to a post cold-drawing process (to reduce the initial diameter) have been studied. The experiments have been performed using magneto-optical Kerr effect and fluxmetric methods in crossed axial and circular magnetic fields. The helical magnetic structure has been found in the surface and in the volume of the wire. The angle of helical anisotropy has been evaluated to be around 45 with respect to the axial direction at the surface of the wire decreasing to 39 through the volume of the wire. r 2004 Elsevier B.V. All rights reserved. PACS: 75.50.Kj; 75.60.Ch; 75.60.Ej Keywords: Amorphous wire; Magneto-optical Kerr effect; Hysteresis loop
1. Introduction During the last few years the amorphous wires have attracted great interest because of their outstanding magnetic properties such as giant magnetoimpedance and magnetic bistability, which makes these materials as potential candidates to be used in sophisticated applications for sensing devices [1–3]. For such applications the low dimension of the sensing element seems to be an important requirement. In this way, a significant reduction of the diameter of the amorphous *Corresponding author. Tel.: +34-943-018611; fax: +34943-212236. E-mail address: [email protected] (A. Chizhik).
wire, obtained by in-rotating-water-quenching technique, can be achieved by a posterior colddrawing process [4–6]. Our paper is devoted to the investigation of the magnetic properties of Fe-rich amorphous wires prepared such as has been mentioned, having the initial diameter of around 0:125 mm to be reduced after cold-drawn process to 0:05 mm: The observation of the magnetoimpedance effect in the wires of this type [7–9] has defined our aspiration to observe and determine the magnetic structure of these wires. The joint application of magneto-optical Kerr effect [10] and fluxmetric methods provides the possibility to obtain interesting information about the different projection of the magnetization as a response to a combination of axial and circular magnetic fields.
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2004.02.004
ARTICLE IN PRESS A. Chizhik et al. / Journal of Magnetism and Magnetic Materials 279 (2004) 359–362
360
2. Experimental details Amorphous wires of nominal composition Fe77:5 B15 Si7:5 and diameter 0:05 mm; obtained by in-rotating-water-quenching technique + colddrawing process, were provided by Goodfellow Company, UK. The wires were submitted to thermal treatment by using a current annealing technique (210 mA during 45 min). Conventional hysteresis loops were measured by fluxmetric method in an AC axial magnetic field of 50 Hz: Surface hysteresis loops have been measured by magneto-optical Kerr effect method in an AC circular magnetic field. During the transverse Kerr effect experiments a polarized light of a He–Ne laser was reflected from the surface of the wire to the detector. The intensity of the reflected light was proportional to the magnetization perpendicular to the plane of the light, i.e. to the circular magnetization in the surface area of the wire. An electrical current flowing along the wire produced a circular magnetic field. A pair of Helmholtz coils has been employed to produce an axial magnetic field. A DC axial and DC circular bias magnetic fields have been applied during the magnetooptical and fluxmetric experiments, respectively.
3. Experimental results and discussion Fig. 1 presents the bulk hysteresis loops measured by the fluxmetric method with DC electric current as a parameter. The magnetization reversal consists of two successive jumps of
M (arb.units)
0.02 0.00 IDC =0 IDC =50mA
-0.02 0
20 HAX (Oe)
40
Fig. 1. Bulk hysteresis loops with DC electric current as a parameter.
magnetization. The shape of the hysteresis loop changes with the DC electric current (i.e. DC circular magnetic field). In particular, the decrease of the switching field for two jumps takes place. Fig. 2 presents the AC circular magnetic field (created by an AC electric current) dependencies of the transverse Kerr effect with the DC axial magnetic field as a parameter. (Figs. 2(e) and (f) show the minor loops). Two successive jumps of the magneto-optical signal in the absence of bias field (Fig. 2(c)) reflect that two jumps of the circular magnetization take place. Under the DC axial magnetic field ðHAXDC Þ (Fig. 2(a), (b), (d)) a transformation of the hysteresis loop is observed. When the HAXDC is positive (Fig. 2(d)), the amplitude of the two jumps changes. The application of small negative bias field causes the disappearing of one of the two jumps (Fig. 2(b)). But when the negative HAXDC is high enough, the reversed second jump appears once more (Fig. 2(a)). The minor loops (Figs. 2(e) and (f)) demonstrate the occurrence of the first jump of surface magnetization. It is necessary to note that the minor loop obtained in the negative HAXDC field is ‘‘reversed’’. Considering that the Kerr effect curves contain information about the magnetization reversal in the surface area of the wire, the observed features of the magneto-optical hysteresis loop could be associated with the existence of a helical anisotropy linked to a helical domain structure in the outer shell of the wire. When the superposition of the circular and axial magnetic field is applied along the direction of this helical anisotropy, only one jump of the magneto-optical signal is observed (Fig. 2(b)). It means that only one jump occurs between two surface domains with the magnetization oriented in the helical direction for this combination of two crossed magnetic fields. The inclination of the superposed magnetic field from this direction causes the appearance of the second jump. The direction of the second jump depends on the direction of the inclination. The transverse Kerr effect signal involves the change of the circular component of the magnetization. Therefore, the specific shape of the hysteresis loop which is presented in the Fig. 2(a), means that for this direction of superposed magnetic field, the
ARTICLE IN PRESS A. Chizhik et al. / Journal of Magnetism and Magnetic Materials 279 (2004) 359–362 0.04
0.04
HAXDC =-1.45 Oe
HAXDC =-1.45 Oe 0.02
0.02
0.00
0.00 -0.02
-0.02
(a) -0.04
361
-0.06 -0.03
0.00
0.03
0.06
-0.04
(e) -0.06 -0.03
0.00
0.03
0.06
0.03
0.06
0.04
Transverse Kerr effect (arb.units)
HAXDC =- 0.34 Oe 0.02 0.00 -0.02 -0.04
(b) -0.06 -0.03
0.00
0.03
0.06
0.04 HAXDC=0 0.02 0.00 -0.02 -0.04
(c) -0.06 -0.03
0.00
0.03
0.06 0.04
0.04 HAXDC=1.45 Oe
HAXDC=1.45 Oe
0.02
0.02
0.00
0.00 -0.02
-0.02 -0.04
(d) -0.06 -0.03
0.00
0.03
0.06
IAC (A)
-0.04
(f) -0.06 -0.03
0.00
IAC (A)
Fig. 2. Transverse Kerr effect hysteresis loops with DC axial magnetic field as a parameter.
direction of the remanent magnetization is more close to the axial direction than to the direction of the helical anisotropy. Therefore, the jump from this inclined remanent condition to the direction of the helical anisotropy takes place at the first stage of the magnetization reversal. This jump is shown individually in the Fig. 2(e). The ‘‘reversed’’ shape of this minor loop reflects the particular increase of the circular magnetization during the magnetization reversal. The value of the angle of the helical anisotropy has been estimated from the magneto-optical
experiments. The value of the circular switching field ðHSWC Þ for the first jump has been obtained from the switching current value (Fig. 2(c)) using the formula for circumferential field HCIRC ¼ Ir=2pR2 : The calculation has been performed for the surface of the wire, i.e. for r ¼ R: The value of HSWC is 0:34 Oe for the value of switching current of 4 mA: Taking into account that the first jump disappears when the axial magnetic field is of 0:34 Oe (Fig. 2(b)), the value of the angle of superposition of the two magnetic fields and accordingly, of the direction of helical anisotropy,
ARTICLE IN PRESS 362
A. Chizhik et al. / Journal of Magnetism and Magnetic Materials 279 (2004) 359–362
could be determined as about 45 with respect to the axial direction. The two jumps of magnetization presented in the bulk hysteresis loop (Fig. 1) could be considered also as the reflection of the existence of a helical anisotropy, but now in the volume of the wire. One of the confirmations of the fact that these jumps are related to the helical anisotropy, is the dependence of the axial switching fields on the DC circular magnetic field (DC electric current). Because of the circular magnetic field has a projection on the helical direction, the jumps occur at lower axial magnetic field in the presence of DC circular magnetic field. The value of the angle of the supposed volume helical structure could be estimated. Taking into account that the volume hysteresis loop is related to the change of the axial projection of the magnetization, the angle of the helical structure could be calculated from the value of the signal, which corresponds to the level of the first jump. This level corresponds to the angle of 39 relatively axial direction. The joint analysis of the surface and bulk hysteresis loops permits us to conclude that the cold-drawing post process induces strong helical anisotropy in the Fe-rich wires studied. The helical magnetic structure exists in the surface and in the volume of the wire. Difference in the value of the angle of the helical anisotropy obtained from the analysis of magneto-optical and fluxmetric
experiments has been found. The angle of the helical anisotropy increases in approach to the surface of the wire. It is necessary to note that the jumps related to the surface and volume helical anisotropy, take place on the background of the jumps, which are associated with the existence of circular (magneto-optical loops) and axial (fluxmetric loops) anisotropies.
References [1] M. V!azquez, A. Hernando, J. Phys. D: Appl. Phys. 29 (1996) 939. [2] K. Kawashima, I. Ogasawara, S. Ueno, K. Mohri, IEEE Trans. Magn. 35 (1999) 3610. [3] R. Hasegawa, J. Magn. Magn. Mater. 249 (2002) 346. [4] R. Malmhall, K. Mohri, F.B. Humphry, T. Manabe, H. Kawamura, J. Yamasaki, I. Ogasawara, IEEE Trans. Magn. 23 (1987) 3242. [5] I. Ogasawara, K. Mohri, IEEE Trans. Magn. 26 (1990) 1795. [6] H. Chiriac, F. Barariu, G. Pop, J. Magn. Magn. Mater. 133 (1994) 325. [7] K.S. Byon, S.C. Yu, C.G. Kim, S.S Yoon, J. Magn. Magn. Mater. 266–230 (2001) 718. [8] V.M. Prida, B. Hernando, M.L. S!anchez, Y.-F. Li, M. Tejedor, M. V!azquez, J. Magn. Magn. Mater. 258–259 (2003) 158. [9] C. Garcia, J. Gonz!alez, A.Chizhik, A. Zhukov, J.M. Blanco, J. Appl. Phys., accepted for publication. [10] A. Chizhik, J. Gonz!alez, A. Zhukov, J.M. Blanco, J. Appl. Phys. 91 (2002) 537.
Journal of Magnetism and Magnetic Materials 279 (2004) 359–362
Investigation of magnetic structure in cold-drawn Fe-rich amorphous wire A. Chizhika,*, C. Garciaa, J. Gonzaleza, J.M. Blancob ! 20080, Spain Departamento F!ısica de Materiales, Facultad de Qu!ımica, UPV, 1072, San Sebastian ! 20018, Spain Departamento F!ısica Aplicada I, EUPDS, UPV/EHU, Plaza Europa, 1, San Sebastian
a b
Received 26 November 2003; received in revised form 26 January 2004
Abstract Magnetic properties of Fe-rich amorphous wires, prepared by in-rotating-water-quenching technique and submitted to a post cold-drawing process (to reduce the initial diameter) have been studied. The experiments have been performed using magneto-optical Kerr effect and fluxmetric methods in crossed axial and circular magnetic fields. The helical magnetic structure has been found in the surface and in the volume of the wire. The angle of helical anisotropy has been evaluated to be around 45 with respect to the axial direction at the surface of the wire decreasing to 39 through the volume of the wire. r 2004 Elsevier B.V. All rights reserved. PACS: 75.50.Kj; 75.60.Ch; 75.60.Ej Keywords: Amorphous wire; Magneto-optical Kerr effect; Hysteresis loop
1. Introduction During the last few years the amorphous wires have attracted great interest because of their outstanding magnetic properties such as giant magnetoimpedance and magnetic bistability, which makes these materials as potential candidates to be used in sophisticated applications for sensing devices [1–3]. For such applications the low dimension of the sensing element seems to be an important requirement. In this way, a significant reduction of the diameter of the amorphous *Corresponding author. Tel.: +34-943-018611; fax: +34943-212236. E-mail address: [email protected] (A. Chizhik).
wire, obtained by in-rotating-water-quenching technique, can be achieved by a posterior colddrawing process [4–6]. Our paper is devoted to the investigation of the magnetic properties of Fe-rich amorphous wires prepared such as has been mentioned, having the initial diameter of around 0:125 mm to be reduced after cold-drawn process to 0:05 mm: The observation of the magnetoimpedance effect in the wires of this type [7–9] has defined our aspiration to observe and determine the magnetic structure of these wires. The joint application of magneto-optical Kerr effect [10] and fluxmetric methods provides the possibility to obtain interesting information about the different projection of the magnetization as a response to a combination of axial and circular magnetic fields.
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2004.02.004
ARTICLE IN PRESS A. Chizhik et al. / Journal of Magnetism and Magnetic Materials 279 (2004) 359–362
360
2. Experimental details Amorphous wires of nominal composition Fe77:5 B15 Si7:5 and diameter 0:05 mm; obtained by in-rotating-water-quenching technique + colddrawing process, were provided by Goodfellow Company, UK. The wires were submitted to thermal treatment by using a current annealing technique (210 mA during 45 min). Conventional hysteresis loops were measured by fluxmetric method in an AC axial magnetic field of 50 Hz: Surface hysteresis loops have been measured by magneto-optical Kerr effect method in an AC circular magnetic field. During the transverse Kerr effect experiments a polarized light of a He–Ne laser was reflected from the surface of the wire to the detector. The intensity of the reflected light was proportional to the magnetization perpendicular to the plane of the light, i.e. to the circular magnetization in the surface area of the wire. An electrical current flowing along the wire produced a circular magnetic field. A pair of Helmholtz coils has been employed to produce an axial magnetic field. A DC axial and DC circular bias magnetic fields have been applied during the magnetooptical and fluxmetric experiments, respectively.
3. Experimental results and discussion Fig. 1 presents the bulk hysteresis loops measured by the fluxmetric method with DC electric current as a parameter. The magnetization reversal consists of two successive jumps of
M (arb.units)
0.02 0.00 IDC =0 IDC =50mA
-0.02 0
20 HAX (Oe)
40
Fig. 1. Bulk hysteresis loops with DC electric current as a parameter.
magnetization. The shape of the hysteresis loop changes with the DC electric current (i.e. DC circular magnetic field). In particular, the decrease of the switching field for two jumps takes place. Fig. 2 presents the AC circular magnetic field (created by an AC electric current) dependencies of the transverse Kerr effect with the DC axial magnetic field as a parameter. (Figs. 2(e) and (f) show the minor loops). Two successive jumps of the magneto-optical signal in the absence of bias field (Fig. 2(c)) reflect that two jumps of the circular magnetization take place. Under the DC axial magnetic field ðHAXDC Þ (Fig. 2(a), (b), (d)) a transformation of the hysteresis loop is observed. When the HAXDC is positive (Fig. 2(d)), the amplitude of the two jumps changes. The application of small negative bias field causes the disappearing of one of the two jumps (Fig. 2(b)). But when the negative HAXDC is high enough, the reversed second jump appears once more (Fig. 2(a)). The minor loops (Figs. 2(e) and (f)) demonstrate the occurrence of the first jump of surface magnetization. It is necessary to note that the minor loop obtained in the negative HAXDC field is ‘‘reversed’’. Considering that the Kerr effect curves contain information about the magnetization reversal in the surface area of the wire, the observed features of the magneto-optical hysteresis loop could be associated with the existence of a helical anisotropy linked to a helical domain structure in the outer shell of the wire. When the superposition of the circular and axial magnetic field is applied along the direction of this helical anisotropy, only one jump of the magneto-optical signal is observed (Fig. 2(b)). It means that only one jump occurs between two surface domains with the magnetization oriented in the helical direction for this combination of two crossed magnetic fields. The inclination of the superposed magnetic field from this direction causes the appearance of the second jump. The direction of the second jump depends on the direction of the inclination. The transverse Kerr effect signal involves the change of the circular component of the magnetization. Therefore, the specific shape of the hysteresis loop which is presented in the Fig. 2(a), means that for this direction of superposed magnetic field, the
ARTICLE IN PRESS A. Chizhik et al. / Journal of Magnetism and Magnetic Materials 279 (2004) 359–362 0.04
0.04
HAXDC =-1.45 Oe
HAXDC =-1.45 Oe 0.02
0.02
0.00
0.00 -0.02
-0.02
(a) -0.04
361
-0.06 -0.03
0.00
0.03
0.06
-0.04
(e) -0.06 -0.03
0.00
0.03
0.06
0.03
0.06
0.04
Transverse Kerr effect (arb.units)
HAXDC =- 0.34 Oe 0.02 0.00 -0.02 -0.04
(b) -0.06 -0.03
0.00
0.03
0.06
0.04 HAXDC=0 0.02 0.00 -0.02 -0.04
(c) -0.06 -0.03
0.00
0.03
0.06 0.04
0.04 HAXDC=1.45 Oe
HAXDC=1.45 Oe
0.02
0.02
0.00
0.00 -0.02
-0.02 -0.04
(d) -0.06 -0.03
0.00
0.03
0.06
IAC (A)
-0.04
(f) -0.06 -0.03
0.00
IAC (A)
Fig. 2. Transverse Kerr effect hysteresis loops with DC axial magnetic field as a parameter.
direction of the remanent magnetization is more close to the axial direction than to the direction of the helical anisotropy. Therefore, the jump from this inclined remanent condition to the direction of the helical anisotropy takes place at the first stage of the magnetization reversal. This jump is shown individually in the Fig. 2(e). The ‘‘reversed’’ shape of this minor loop reflects the particular increase of the circular magnetization during the magnetization reversal. The value of the angle of the helical anisotropy has been estimated from the magneto-optical
experiments. The value of the circular switching field ðHSWC Þ for the first jump has been obtained from the switching current value (Fig. 2(c)) using the formula for circumferential field HCIRC ¼ Ir=2pR2 : The calculation has been performed for the surface of the wire, i.e. for r ¼ R: The value of HSWC is 0:34 Oe for the value of switching current of 4 mA: Taking into account that the first jump disappears when the axial magnetic field is of 0:34 Oe (Fig. 2(b)), the value of the angle of superposition of the two magnetic fields and accordingly, of the direction of helical anisotropy,
ARTICLE IN PRESS 362
A. Chizhik et al. / Journal of Magnetism and Magnetic Materials 279 (2004) 359–362
could be determined as about 45 with respect to the axial direction. The two jumps of magnetization presented in the bulk hysteresis loop (Fig. 1) could be considered also as the reflection of the existence of a helical anisotropy, but now in the volume of the wire. One of the confirmations of the fact that these jumps are related to the helical anisotropy, is the dependence of the axial switching fields on the DC circular magnetic field (DC electric current). Because of the circular magnetic field has a projection on the helical direction, the jumps occur at lower axial magnetic field in the presence of DC circular magnetic field. The value of the angle of the supposed volume helical structure could be estimated. Taking into account that the volume hysteresis loop is related to the change of the axial projection of the magnetization, the angle of the helical structure could be calculated from the value of the signal, which corresponds to the level of the first jump. This level corresponds to the angle of 39 relatively axial direction. The joint analysis of the surface and bulk hysteresis loops permits us to conclude that the cold-drawing post process induces strong helical anisotropy in the Fe-rich wires studied. The helical magnetic structure exists in the surface and in the volume of the wire. Difference in the value of the angle of the helical anisotropy obtained from the analysis of magneto-optical and fluxmetric
experiments has been found. The angle of the helical anisotropy increases in approach to the surface of the wire. It is necessary to note that the jumps related to the surface and volume helical anisotropy, take place on the background of the jumps, which are associated with the existence of circular (magneto-optical loops) and axial (fluxmetric loops) anisotropies.
References [1] M. V!azquez, A. Hernando, J. Phys. D: Appl. Phys. 29 (1996) 939. [2] K. Kawashima, I. Ogasawara, S. Ueno, K. Mohri, IEEE Trans. Magn. 35 (1999) 3610. [3] R. Hasegawa, J. Magn. Magn. Mater. 249 (2002) 346. [4] R. Malmhall, K. Mohri, F.B. Humphry, T. Manabe, H. Kawamura, J. Yamasaki, I. Ogasawara, IEEE Trans. Magn. 23 (1987) 3242. [5] I. Ogasawara, K. Mohri, IEEE Trans. Magn. 26 (1990) 1795. [6] H. Chiriac, F. Barariu, G. Pop, J. Magn. Magn. Mater. 133 (1994) 325. [7] K.S. Byon, S.C. Yu, C.G. Kim, S.S Yoon, J. Magn. Magn. Mater. 266–230 (2001) 718. [8] V.M. Prida, B. Hernando, M.L. S!anchez, Y.-F. Li, M. Tejedor, M. V!azquez, J. Magn. Magn. Mater. 258–259 (2003) 158. [9] C. Garcia, J. Gonz!alez, A.Chizhik, A. Zhukov, J.M. Blanco, J. Appl. Phys., accepted for publication. [10] A. Chizhik, J. Gonz!alez, A. Zhukov, J.M. Blanco, J. Appl. Phys. 91 (2002) 537.