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Investigation of surface magnetization reversal in Co-rich amorphous microwires with magneto-impedance effect
ARTICLE IN PRESS
Physica B 384 (2006) 5–8 www.elsevier.com/locate/physb
Investigation of surface magnetization reversal in Co-rich amorphous microwires with magneto-impedance effect A. Chizhika, C. Garciaa, A. Zhukova, J. Gonzaleza,, L. Dominguezb, J.M. Blancob a
Dpto Fisica de Materiales, Facultad de Quimica, UPV, 1072, 20080 San Sebastian, Spain b Departamento Fisica Aplicada I, EUPDS, UPV/EHU, 20018 San Sebastian, Spain
Abstract Investigation of the surface magnetization reversal and the magnetoimpedance (MI) effect have been performed in Co-rich glasscovered microwires with identical composition and different thickness of glass covering. The correlation between the mechanism of the surface magnetization reversal and the value of MI effect has been discovered. The Kerr effect study showed that the bias magnetic field induces shift of circular hysteresis loop. This shift could be considered as a characteristic feature of the high value of the MI ratio. r 2006 Elsevier B.V. All rights reserved. PACS: 75.50.Kj; 75.60.Ch; 75.60.Ej Keywords: Amorphous wire; Kerr effect; GMI effect
Giant magnetoimpedance (GMI) effect, discovered in amorphous wires [1,2], is based on the change of the surface dynamic magnetization caused by high-frequency circular and DC axial magnetic field. Our previous investigation of GMI and surface magneto-optical Kerr effect (MOKE) [3] demonstrated the correlation between the surface magnetization reversal and the magnetoimpedance (MI) properties. In the present work, we study surface magnetization reversal in Co-rich glass-covered microwires with identical composition and different thickness of glass covering. The purpose of this investigation was to find the correlation between the different mechanisms of the surface magnetization reversal and the value of GMI effect. Glass covered amorphous microwires of nominal composition Co69.5Fe3.9Ni1B11.8Si10.8Mo2 were obtained by the Taylor–Ulitovski method [4,5]. Four microwires with different geometric ratio, r, of metallic nucleus diameter, d, to total microwire diameter, D, 0.79, 0.88, 0.90 and 0.93 have been studied. The experiments have been performed using transverse MOKE. A circular magnetic field has been Corresponding author. Fax: +34 943 017130.
E-mail address: [email protected] (J. Gonzalez). 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.05.021
produced by an electric current flowing through the wire. The intensity of the light reflected from the wire was proportional to the circular projection of the magnetization in the surface area of the wire. The electrical impedance of the microwires was evaluated by means of a network analyzer. Fig. 1 presents the MOKE dependencies on the AC electric current flowing along the wires with DC axial field as a parameter. Fig. 2 presents the MOKE effect dependencies on the AC axial field. When the DC axial magnetic field is absent, the shape of the circular hysteresis loop is perfectly rectangular (Fig. 1(a and d)). The DC axial magnetic field initiates the transformation of the circular hysteresis loop in two different ways. Figs. 1(b and c) demonstrate the shape of the hysteresis loop for the wire with r ¼ 0:90 and 0.93 in the presence of the axial DC bias magnetic field. The application of the DC axial magnetic field causes the asymmetrical change of the switching field, HSW (associated with the switching current). The value of H þ SW increases when the value of H decreases. This effect is realized in the observed SW ‘‘shift’’ of the hysteresis loop along the X-axis. When the sign of the DC axial magnetic field changes to the opposite
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A. Chizhik et al. / Physica B 384 (2006) 5–8
Fig. 1. Transverse Kerr effect dependencies on electric current (circular magnetic field) with the axial bias field as a parameter.
one, the picture reverses: H þ SW decreases and H SW increases. The transformation of the circular hysteresis loop for the wires with r ¼ 0:79 and 0.88 occurs in another way. The þ absolute values of H SW and H SW decreases symmetrically and the ‘‘shift’’ effect is not observed (Figs. 1(e and f)). The application of the negative axial magnetic field causes the transformation of the hysteresis loop in the same way as the positive one. The difference also takes place in the hysteresis loops obtained in the AC axial magnetic field (Fig. 2). As we see earlier [6], the surface magnetization reversal in Co-rich microwires consists of rotation of the magnetization and
the nucleation of the circular domains. First, when the external axial magnetic field increases the rotation of the magnetization from axial direction to circular direction is observed. After that, the sharp jump of the signal with the change of the signal sign takes place. This is related to the nucleation of circular domain. For the wires with r ¼ 0:90 and 0.93 the jump of magnetization in high enough. For the wires with r ¼ 0:79 and 0.88 the magnetization reversal consists mainly of the rotation of the magnetization. The jump of the magnetization related to the nucleation of the circular domains is relatively small. The axial field dependence of the MI ratio DZ=Z measured at fixed AC driving current amplitude of 1 mA
ARTICLE IN PRESS A. Chizhik et al. / Physica B 384 (2006) 5–8
7
Fig. 2. Transverse Kerr effect dependencies on axial magnetic field for four wires with different thickness of glass covering.
Fig. 3. Axial field dependence of the MI for four wires with different thickness of glass covering.
and frequency 10 MHz is presented in the Fig. 3. The MI ratio has been defined as DZ=Z ¼ ½ZðHÞ ZðH max Þ= ZðH max Þ. The maximum value of the MI ratio has been obtained for the wire with r ¼ 0:90. The main difference between the hysteresis loops presented in the Fig. 1 is the existence of the shift of hysteresis loop for the r ¼ 0:9 and 0.93 and the absence of this shift for the r ¼ 0:79 and 0.88. For the wires with r ¼ 0:79 and 0.88 the DC axial magnetic field causes only the inclination of the magnetization in the outer shell of the wire towards the axial direction (Fig. 1(e and f)). This inclination takes place in the same way in circular domains þ (+) and (). The H SW and H SW decrease in the presence of axial DC field because the DC magnetic field favors the nucleation of a circular domain of two types. For the wires with r ¼ 0:90 and 0.93, the DC magnetic field favors the nucleation of a circular domain of one type and delays the nucleation of the domains of the other type. The observed correlation of the signs of the axial magnetic field and the nucleated circular domain is the main difference of these wires. The axial field has direct influence on the nucleation of the axial domain. The observed shift
of the surface loop reflects the strong correlation between the axial domain of defined direction and the circular domain of the defined direction in the outer shell. The main conclusion from this experiment is that for the wires with r ¼ 0:79 and 0.88 the DC axial field initiates mainly the inclination of the magnetization in the outer shell. For the wires with r ¼ 0:90 and 0.93 the DC axial magnetic field supports the nucleation of circular domain but not the rotation of the magnetization. This process of nucleation is accompanied by the formation and the motion of circular domain walls that leads to the increase of the circular permeability. In AC axial field (Fig. 2), for the wires with r ¼ 0:90 and 0.93 the nucleation of circular domain occurs just after the magnetization has reached the circular direction. For the wires with r ¼ 0:79 and 0.88 the rotation of magnetization continues after the reaching of the maximal point of the circular magnetization and the nucleation occurs later. In this situation the magnetization reversal is determined basically by the rotation of the magnetization and the value of the jump of magnetization related to the nucleation of the circular domain is small. From this experiment we can conclude that the contribution of the domain walls motion to the magnetization reversal is smaller for the wires with r ¼ 0:79 and 0.88 than for the wires with r ¼ 0:90 and 0.93. The meaning of the above-mentioned MOKE experiments is following. The jump of circular magnetization and the circular domain wall dynamics related to it, determines essentially the circumferential permeability. In turn, MI effect is closely associated with the circumferential permeability. In the MOKE experiments the jump of the circular magnetization is smaller for the wires with r ¼ 0:79 and 0.88 than for the wires with r ¼ 0:90 and 0.93. It finds the reflection in the smaller value of the circumferential permeability and the smaller value the MI ratio. In the present study the series of the glass-covered microwires was considered as a model one having some distribution of the GMI value. Therefore we do not discuss in this paper the reason of the influence of the glass covering on the surface magnetic properties. Generally, the surface magnetic structure in the glass-covered microwires
ARTICLE IN PRESS 8
A. Chizhik et al. / Physica B 384 (2006) 5–8
originates from the magnetoelastic anisotropy associated with the internal stresses. One of the sources of these stresses is the difference of the thermal expansion coefficients of the glass coating and metallic nucleus [7]. Concluding, the surface magnetization reversal has been studied in Co-rich glass-covered microwires with different thickness of glass covering, which demonstrate great difference in the MI ratio. The difference in the mechanism of the surface magnetization reversal has been discovered. The DC axial magnetic field shift of circular hysteresis loop could be considered as a characteristic attribute of high value of MI. The value of the jump of the circular magnetization has the correlation with the circular permeability and in such a way with the value of GMI. Therefore, we can conclude that the value of the MI could be
predicted based on the analysis of the shape of the surface magnetization reversal curves.
References [1] R.S. Beach, A.E. Berkowitz, Appl. Phys. Lett. 64 (1994) 3652. [2] L.V. Panina, K. Mohri, Appl. Phys. Lett. 65 (1994) 1189. [3] V. Zhukova, A. Chizhik, A. Zhukov, A. Torcunov, V. Larin, J. Gonzalez, IEEE Trans. Mag. 38 (2002) 3090. [4] G.F. Taylor, Phys. Rev. 24 (1924) 6555. [5] M. Vazquez, A. Zhukov, J. Magn. Magn. Mater. 160 (1996) 223. [6] A. Chizhik, J. Gonzalez, A. Zhukov, J.M. Blanco, Appl. Phys. Lett. 82 (2003) 610. [7] A. Zhukov, J. Gonzalez, J.M. Blanco, M.J. Prieto, E. Pina, M. Vazquez, J. Appl. Phys. 87 (2000) 1402.
Physica B 384 (2006) 5–8 www.elsevier.com/locate/physb
Investigation of surface magnetization reversal in Co-rich amorphous microwires with magneto-impedance effect A. Chizhika, C. Garciaa, A. Zhukova, J. Gonzaleza,, L. Dominguezb, J.M. Blancob a
Dpto Fisica de Materiales, Facultad de Quimica, UPV, 1072, 20080 San Sebastian, Spain b Departamento Fisica Aplicada I, EUPDS, UPV/EHU, 20018 San Sebastian, Spain
Abstract Investigation of the surface magnetization reversal and the magnetoimpedance (MI) effect have been performed in Co-rich glasscovered microwires with identical composition and different thickness of glass covering. The correlation between the mechanism of the surface magnetization reversal and the value of MI effect has been discovered. The Kerr effect study showed that the bias magnetic field induces shift of circular hysteresis loop. This shift could be considered as a characteristic feature of the high value of the MI ratio. r 2006 Elsevier B.V. All rights reserved. PACS: 75.50.Kj; 75.60.Ch; 75.60.Ej Keywords: Amorphous wire; Kerr effect; GMI effect
Giant magnetoimpedance (GMI) effect, discovered in amorphous wires [1,2], is based on the change of the surface dynamic magnetization caused by high-frequency circular and DC axial magnetic field. Our previous investigation of GMI and surface magneto-optical Kerr effect (MOKE) [3] demonstrated the correlation between the surface magnetization reversal and the magnetoimpedance (MI) properties. In the present work, we study surface magnetization reversal in Co-rich glass-covered microwires with identical composition and different thickness of glass covering. The purpose of this investigation was to find the correlation between the different mechanisms of the surface magnetization reversal and the value of GMI effect. Glass covered amorphous microwires of nominal composition Co69.5Fe3.9Ni1B11.8Si10.8Mo2 were obtained by the Taylor–Ulitovski method [4,5]. Four microwires with different geometric ratio, r, of metallic nucleus diameter, d, to total microwire diameter, D, 0.79, 0.88, 0.90 and 0.93 have been studied. The experiments have been performed using transverse MOKE. A circular magnetic field has been Corresponding author. Fax: +34 943 017130.
E-mail address: [email protected] (J. Gonzalez). 0921-4526/$ - see front matter r 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.physb.2006.05.021
produced by an electric current flowing through the wire. The intensity of the light reflected from the wire was proportional to the circular projection of the magnetization in the surface area of the wire. The electrical impedance of the microwires was evaluated by means of a network analyzer. Fig. 1 presents the MOKE dependencies on the AC electric current flowing along the wires with DC axial field as a parameter. Fig. 2 presents the MOKE effect dependencies on the AC axial field. When the DC axial magnetic field is absent, the shape of the circular hysteresis loop is perfectly rectangular (Fig. 1(a and d)). The DC axial magnetic field initiates the transformation of the circular hysteresis loop in two different ways. Figs. 1(b and c) demonstrate the shape of the hysteresis loop for the wire with r ¼ 0:90 and 0.93 in the presence of the axial DC bias magnetic field. The application of the DC axial magnetic field causes the asymmetrical change of the switching field, HSW (associated with the switching current). The value of H þ SW increases when the value of H decreases. This effect is realized in the observed SW ‘‘shift’’ of the hysteresis loop along the X-axis. When the sign of the DC axial magnetic field changes to the opposite
ARTICLE IN PRESS 6
A. Chizhik et al. / Physica B 384 (2006) 5–8
Fig. 1. Transverse Kerr effect dependencies on electric current (circular magnetic field) with the axial bias field as a parameter.
one, the picture reverses: H þ SW decreases and H SW increases. The transformation of the circular hysteresis loop for the wires with r ¼ 0:79 and 0.88 occurs in another way. The þ absolute values of H SW and H SW decreases symmetrically and the ‘‘shift’’ effect is not observed (Figs. 1(e and f)). The application of the negative axial magnetic field causes the transformation of the hysteresis loop in the same way as the positive one. The difference also takes place in the hysteresis loops obtained in the AC axial magnetic field (Fig. 2). As we see earlier [6], the surface magnetization reversal in Co-rich microwires consists of rotation of the magnetization and
the nucleation of the circular domains. First, when the external axial magnetic field increases the rotation of the magnetization from axial direction to circular direction is observed. After that, the sharp jump of the signal with the change of the signal sign takes place. This is related to the nucleation of circular domain. For the wires with r ¼ 0:90 and 0.93 the jump of magnetization in high enough. For the wires with r ¼ 0:79 and 0.88 the magnetization reversal consists mainly of the rotation of the magnetization. The jump of the magnetization related to the nucleation of the circular domains is relatively small. The axial field dependence of the MI ratio DZ=Z measured at fixed AC driving current amplitude of 1 mA
ARTICLE IN PRESS A. Chizhik et al. / Physica B 384 (2006) 5–8
7
Fig. 2. Transverse Kerr effect dependencies on axial magnetic field for four wires with different thickness of glass covering.
Fig. 3. Axial field dependence of the MI for four wires with different thickness of glass covering.
and frequency 10 MHz is presented in the Fig. 3. The MI ratio has been defined as DZ=Z ¼ ½ZðHÞ ZðH max Þ= ZðH max Þ. The maximum value of the MI ratio has been obtained for the wire with r ¼ 0:90. The main difference between the hysteresis loops presented in the Fig. 1 is the existence of the shift of hysteresis loop for the r ¼ 0:9 and 0.93 and the absence of this shift for the r ¼ 0:79 and 0.88. For the wires with r ¼ 0:79 and 0.88 the DC axial magnetic field causes only the inclination of the magnetization in the outer shell of the wire towards the axial direction (Fig. 1(e and f)). This inclination takes place in the same way in circular domains þ (+) and (). The H SW and H SW decrease in the presence of axial DC field because the DC magnetic field favors the nucleation of a circular domain of two types. For the wires with r ¼ 0:90 and 0.93, the DC magnetic field favors the nucleation of a circular domain of one type and delays the nucleation of the domains of the other type. The observed correlation of the signs of the axial magnetic field and the nucleated circular domain is the main difference of these wires. The axial field has direct influence on the nucleation of the axial domain. The observed shift
of the surface loop reflects the strong correlation between the axial domain of defined direction and the circular domain of the defined direction in the outer shell. The main conclusion from this experiment is that for the wires with r ¼ 0:79 and 0.88 the DC axial field initiates mainly the inclination of the magnetization in the outer shell. For the wires with r ¼ 0:90 and 0.93 the DC axial magnetic field supports the nucleation of circular domain but not the rotation of the magnetization. This process of nucleation is accompanied by the formation and the motion of circular domain walls that leads to the increase of the circular permeability. In AC axial field (Fig. 2), for the wires with r ¼ 0:90 and 0.93 the nucleation of circular domain occurs just after the magnetization has reached the circular direction. For the wires with r ¼ 0:79 and 0.88 the rotation of magnetization continues after the reaching of the maximal point of the circular magnetization and the nucleation occurs later. In this situation the magnetization reversal is determined basically by the rotation of the magnetization and the value of the jump of magnetization related to the nucleation of the circular domain is small. From this experiment we can conclude that the contribution of the domain walls motion to the magnetization reversal is smaller for the wires with r ¼ 0:79 and 0.88 than for the wires with r ¼ 0:90 and 0.93. The meaning of the above-mentioned MOKE experiments is following. The jump of circular magnetization and the circular domain wall dynamics related to it, determines essentially the circumferential permeability. In turn, MI effect is closely associated with the circumferential permeability. In the MOKE experiments the jump of the circular magnetization is smaller for the wires with r ¼ 0:79 and 0.88 than for the wires with r ¼ 0:90 and 0.93. It finds the reflection in the smaller value of the circumferential permeability and the smaller value the MI ratio. In the present study the series of the glass-covered microwires was considered as a model one having some distribution of the GMI value. Therefore we do not discuss in this paper the reason of the influence of the glass covering on the surface magnetic properties. Generally, the surface magnetic structure in the glass-covered microwires
ARTICLE IN PRESS 8
A. Chizhik et al. / Physica B 384 (2006) 5–8
originates from the magnetoelastic anisotropy associated with the internal stresses. One of the sources of these stresses is the difference of the thermal expansion coefficients of the glass coating and metallic nucleus [7]. Concluding, the surface magnetization reversal has been studied in Co-rich glass-covered microwires with different thickness of glass covering, which demonstrate great difference in the MI ratio. The difference in the mechanism of the surface magnetization reversal has been discovered. The DC axial magnetic field shift of circular hysteresis loop could be considered as a characteristic attribute of high value of MI. The value of the jump of the circular magnetization has the correlation with the circular permeability and in such a way with the value of GMI. Therefore, we can conclude that the value of the MI could be
predicted based on the analysis of the shape of the surface magnetization reversal curves.
References [1] R.S. Beach, A.E. Berkowitz, Appl. Phys. Lett. 64 (1994) 3652. [2] L.V. Panina, K. Mohri, Appl. Phys. Lett. 65 (1994) 1189. [3] V. Zhukova, A. Chizhik, A. Zhukov, A. Torcunov, V. Larin, J. Gonzalez, IEEE Trans. Mag. 38 (2002) 3090. [4] G.F. Taylor, Phys. Rev. 24 (1924) 6555. [5] M. Vazquez, A. Zhukov, J. Magn. Magn. Mater. 160 (1996) 223. [6] A. Chizhik, J. Gonzalez, A. Zhukov, J.M. Blanco, Appl. Phys. Lett. 82 (2003) 610. [7] A. Zhukov, J. Gonzalez, J.M. Blanco, M.J. Prieto, E. Pina, M. Vazquez, J. Appl. Phys. 87 (2000) 1402.