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Giant magneto-impedance effect in Fe4.5Co67.5Mn0.5Si12B15 amorphous wires
Materials Science and Engineering A304–306 (2001) 954–956
Giant magneto-impedance effect in Fe4.5Co67.5Mn0.5Si12 B15 amorphous wires S.X. Zhou a,∗ , Jifan Hu a , B.Y. Quan b a
National Amorphous & Nanocrystalline Alloy Engineering Research Center, Central Iron & Steel Research Institute, Beijing 100081, China b Department of Physics, Shandong University, Jinan 250100, China
Abstract The Giant magneto-impedance of amorphous wires with a nominal composition of Fe4.5 Co67.5 Nb0.5 Mn0.5 Si12 B15 has been investigated using a HP4192A impedance analyzer in the frequency range from 5 Hz to 13 MHz. The results show that there exists an optimum frequency where the GMI shows a maximum for all samples investigated, and the maximum GMI values of the as-cast wire and the wire annealed at 350◦ C are 73 and 71%, respectively. GMI effect for the as-cast wire at the frequency range <1 MHz is much higher than those for the annealed samples, and in the case of frequency range >1 MHz GMI effect is better than that of the as-cast state. GMI(Z)max shows a maximum with annealing temperature and optimum annealing temperature is 350◦ C in the study. Both magneto-resistance and magneto-reactance of the as-cast wire have also been investigated. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Giant magneto-impedance; Amorphous wires; Earth magnetic field
1. Introduction Recently, giant magneto-impedance (GMI) effect of Co-based amorphous wire has attracted great attention and widely studied due to its possible application in magnetic sensor and recording head [1–7]. The strongest GMI effect was observed in an amorphous wire of a composition of Fe4.3 Co68.2 Si12.5 B15 with a nearly zero magneto-striction constant. For FeCoSiB amorphous wire, the giant magneto-induction occurs in a low frequency range of 1–10 kHz, and the inductive component of an ac wire voltage decreases by 50% for a longitudinal field of 2–5 Oe. At higher frequencies (0.1–10 MHz), where the skin effect is essential, the giant magneto-impedance appears. Both resistive and inductive component of impedance for FeCoSiB amorphous wire strongly changes with dc magnetic field. The amplitude of the total wire voltage decreases by 40–60% under the influence of a longitudinal field of 3–10 Oe [4]. The GMI effect is a classical electromagnetic phenomenon, which depends essentially on the interaction between the magnetic field created by the ac current and magnetic domains of the sample. In the case of strong skin effect, the total wire impedance is closely related to the circumferential permeability through the penetration depth [3,4].
∗
Corresponding author.
The residual stress introduced during solidification process results in the complicated domain structure. A positive magneto-strictive amorphous wire has closure domains in outer-shell, while a negative magneto-strictive amorphous wire generates bamboo domain in outer-shell [4]. In the inner core, an axial anisotropy is induced due to the shape effect during low cooling rate. The special domain structure influences strongly on the GMI effect. Therefore, the GMI effect in the amorphous wire varies under the application of the tension and annealing with tension. In fact, domain is the thermal-sensitive property, GMI effect in wire may be changed by the simple annealing without tension. In the present work, we reported the giant magneto-impedance effect in Fe4.5 Co67.5 Nb0.5 Mn0.5 Si12 B15 amorphous wires. 2. Experiments Amorphous wires with a nominal composition of Fe4.5 Co67.5 Nb0.5 Mn0.5 Si12 B15 were prepared by in-rotatingwater spinning process. The samples were subsequently annealed at the temperatures from 300 to 450◦ C for 30 min, respectively. All of the data presented in the work were measured using a HP4192A impedance analyzer with the frequency range of 5 Hz–13 MHz. The samples were connected to the analyzer with the accessory 16048B test lead, which is a carefully designed unit with four coaxial cables. A pair of Helmholtz coils (30 cm in diameter) was used to generate an applied dc magnetic field in the range of
0921-5093/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 5 0 9 3 ( 0 0 ) 0 1 6 0 1 - 4
S.X. Zhou et al. / Materials Science and Engineering A304–306 (2001) 954–956
955
0–70 Oe. The coils are so placed that the applied field is perpendicular to the earth magnetic field. 3. Results and discussion Fig. 1 shows the frequency dependence of the impedance ratios |[Z(65 Oe) − Z(0)]/Z(0)| for the as-cast sample and samples annealed at temperatures of 300 350, 400, and 450◦ C for 30 min, respectively. Here Z(65 Oe) and Z(0) represent the impedance at dc magnetic field of H = 65 and 0 Oe. It can be seen that the GMI value of the as-cast wire is larger than those of the annealed wires. There exists an optimum frequency where the value of |[Z(65 Oe) − Z(0)]/Z(0)| has a maximum for all samples investigated. The maximum phenomenon is evident for annealed wires, whereas the peak phenomenon for the as-cast wire is too small to be observed. The frequency (fmax ) of annealed wires where the maximum GMI value occurs, is higher than that of the as-cast wire. The frequency (fmax ) for the as-cast wire is 0.3 MHz and is about 1 MHz for the wire annealed at 350◦ C. It is worthy to note that the maximum GMI value, GMI(Z)max is 73% for the as-cast wire and is 71% for the wire annealed at 350◦ C. Below 1 MHz, the GMI(Z) value of the as-cast wire is larger than those of the wires annealed at different temperatures. Above 1 MHz, the GMI(Z) value of the wire annealed at 350◦ C is the largest in all samples investigated. Fig. 2 shows the annealing temperature dependence of GMI(Z)max = |[Z(65 Oe)−Z(0)]/Z(0)|max measured from all annealed samples. It is evident that GMI(Z)max increases with increasing annealing temperature up to a maximum and then drops after 350◦ C. This implies that the annealing temperature should not be too high. Otherwise the samples tend to be crystallized and GMI value drops sharply. Such behavior is different from the case of FeCuNbSiB wires [8]. The largest GMI comes from the nanocrystalline state for FeCuNbSiB wires. Fig. 3 shows the dc field dependence of GMI value [Z(H ) − Z(0)]/Z(0) for the as-cast wire. It can be seen
Fig. 1. Frequency dependence of the GMI value of the as-cast and annealed amorphous wires.
Fig. 2. Dependence of the GMI value of the amorphous wires on annealing temperatures.
that at a low frequency of 0.1 MHz the GMI value decreases with increasing dc magnetic field. At high frequency range such as 1 and 12 MHz, there exists a peak phenomenon in the dc field dependence of GMI. Such peak phenomenon is associated with the circumferential anisotropy. The circumferential anisotropy field HK corresponds to the peak-field HP , where the peak occurs and varies with ac frequency [4]. The value of HK is the function of the ac frequency (f). It can be seen from Fig. 3 that HK (1 MHz) < H K (12 MHz). It has also been found that at high frequencies the skin effect becomes pronounced and the total wire impedance depends on the circumferential permeability through the penetration depth. There are two different kinds of contributions to the effective permeability [4]: (1) domain wall movement and (2) magnetization rotation. At low frequencies when the external field Hex is lower than HK the mechanism of domain wall movement dominates the effective permeability. With increasing frequency the rotation permeability becomes important even at H ex < H K since the wall movement becomes more and more damped. The longitudinal external field stimulates the rotational process while H ex < H K and the corresponding permeability has a
Fig. 3. Dependence of GMI value of the as-cast amorphous wire on dc applied field.
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S.X. Zhou et al. / Materials Science and Engineering A304–306 (2001) 954–956
Fig. 6. Dependence of magneto-reactance of the as-cast amorphous wire on dc applied field at the frequencies of 0.1 and 12 MHz. Fig. 4. Dependence of GMI value of the amorphous wires annealed at 350◦ C on dc applied field.
maximum at H ex = H K . The dc field dependence of GMI value with different ac frequencies for the wire annealed at 350◦ C is shown in Fig. 4. The peak phenomenon can be found at 12 MHz but not at 1 MHz. Compared with the case of the as-cast wire the circumferential anisotropy field HK changes very little which is about 8 Oe. In order to give more information on GMI for Fe4.5 Co67.5 Nb0.5 Mn0.5 Si12 B15 amorphous wires, the dc field dependence of the magneto-resistance [R(H ) − R(0)]/R(0) and magneto-reactance [X(H ) − X(0)]/X(0) for the as-cast sample are investigated as shown in Figs. 5 and 6. It can be seen from Fig. 5 that with increasing dc field the value of magneto-resistance ratio [R(H ) − R(0)]/R(0) decreases monotonously at the frequency of 0.1 MHz, whereas in the case of frequency, f = 12 MHz, the magneto-resistance ratio increases firstly undergoes a peak in positive value and finally drops again. The peak value of [R(H ) − R(0)]/R(0) at 12 MHz reaches about 60%. It is evident from Fig. 6 that with increasing dc field the magneto-reactance ratio, [X(H ) − X(0)]/X(0), exhibits the peak-phenomenon in both 12 and 0.1 MHz, and the peak field HP at 12 MHz
is larger than that at 0.1 MHz. It should be noticed that in Fig. 3 no evident peak of GMI is observed at the frequency of 0.1 MHz with applied field. However, from the curve of magneto-reactance versus applied field in Fig. 6, a well-defined peak is observed at the frequency of 0.1 MHz. This may be because of the value of reactance for the as-cast wires is much less than that of resistance at low frequency range [6].
4. Conclusions The following conclusions may be drawn from the investigations. 1. There exists an optimum frequency where the GMI shows a maximum for all samples investigated, and the maximum GMI values of the as-cast wire and the wire annealed at 350◦ C are 73 and 71%, respectively. 2. GMI effect for the as-cast wire in the frequency range <1 MHz is much higher than those for the annealed samples, and in the case of frequency range >1 MHz GMI effect is better than that of the as-cast state. 3. GMI(Z)max shows a maximum with annealing temperature, the optimum annealing temperature is 350◦ C in the study. References
Fig. 5. Dependence of magneto-resistance of the as-cast amorphous wire on dc applied field at the frequencies of 0.1 and 12 MHz.
[1] K. Mohri, K. Kawashima, T. Kohzawa, Y. Yoshida, L.V. Panina, IEEE Trans. Magn. 28 (1992) 3150. [2] K. Mohri, K. Kawashima, T. Kohzawa, Y. Yoshida, IFEE Trans. Magn. 29 (1993) 1245. [3] R.S. Beach, A.E. Berkowitz, Appl. Phys. Lett. 64 (1994) 3682. [4] L.V. Panina, K. Mohri, T. Uchiyama, M. Noda, IEFE Trans. Magn. 31 (1995) 1249. [5] D. Atkinson, P.T. Squire, IEEE Trans. Magn. 33 (1997) 3364. [6] S.X. Zhou, J.F. Hu, Met. Func. Mater. 5 (1998) 19 (in Chinese). [7] J.F. Hu, S.X. Zhou, Met. Func. Mater. 6 (1999) 21 (in Chinese). [8] H. Chiriac, T.A. Ovari, C.S. Marinescu, J. Appl. Phys. 83 (1998) 6584.
Giant magneto-impedance effect in Fe4.5Co67.5Mn0.5Si12 B15 amorphous wires S.X. Zhou a,∗ , Jifan Hu a , B.Y. Quan b a
National Amorphous & Nanocrystalline Alloy Engineering Research Center, Central Iron & Steel Research Institute, Beijing 100081, China b Department of Physics, Shandong University, Jinan 250100, China
Abstract The Giant magneto-impedance of amorphous wires with a nominal composition of Fe4.5 Co67.5 Nb0.5 Mn0.5 Si12 B15 has been investigated using a HP4192A impedance analyzer in the frequency range from 5 Hz to 13 MHz. The results show that there exists an optimum frequency where the GMI shows a maximum for all samples investigated, and the maximum GMI values of the as-cast wire and the wire annealed at 350◦ C are 73 and 71%, respectively. GMI effect for the as-cast wire at the frequency range <1 MHz is much higher than those for the annealed samples, and in the case of frequency range >1 MHz GMI effect is better than that of the as-cast state. GMI(Z)max shows a maximum with annealing temperature and optimum annealing temperature is 350◦ C in the study. Both magneto-resistance and magneto-reactance of the as-cast wire have also been investigated. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Giant magneto-impedance; Amorphous wires; Earth magnetic field
1. Introduction Recently, giant magneto-impedance (GMI) effect of Co-based amorphous wire has attracted great attention and widely studied due to its possible application in magnetic sensor and recording head [1–7]. The strongest GMI effect was observed in an amorphous wire of a composition of Fe4.3 Co68.2 Si12.5 B15 with a nearly zero magneto-striction constant. For FeCoSiB amorphous wire, the giant magneto-induction occurs in a low frequency range of 1–10 kHz, and the inductive component of an ac wire voltage decreases by 50% for a longitudinal field of 2–5 Oe. At higher frequencies (0.1–10 MHz), where the skin effect is essential, the giant magneto-impedance appears. Both resistive and inductive component of impedance for FeCoSiB amorphous wire strongly changes with dc magnetic field. The amplitude of the total wire voltage decreases by 40–60% under the influence of a longitudinal field of 3–10 Oe [4]. The GMI effect is a classical electromagnetic phenomenon, which depends essentially on the interaction between the magnetic field created by the ac current and magnetic domains of the sample. In the case of strong skin effect, the total wire impedance is closely related to the circumferential permeability through the penetration depth [3,4].
∗
Corresponding author.
The residual stress introduced during solidification process results in the complicated domain structure. A positive magneto-strictive amorphous wire has closure domains in outer-shell, while a negative magneto-strictive amorphous wire generates bamboo domain in outer-shell [4]. In the inner core, an axial anisotropy is induced due to the shape effect during low cooling rate. The special domain structure influences strongly on the GMI effect. Therefore, the GMI effect in the amorphous wire varies under the application of the tension and annealing with tension. In fact, domain is the thermal-sensitive property, GMI effect in wire may be changed by the simple annealing without tension. In the present work, we reported the giant magneto-impedance effect in Fe4.5 Co67.5 Nb0.5 Mn0.5 Si12 B15 amorphous wires. 2. Experiments Amorphous wires with a nominal composition of Fe4.5 Co67.5 Nb0.5 Mn0.5 Si12 B15 were prepared by in-rotatingwater spinning process. The samples were subsequently annealed at the temperatures from 300 to 450◦ C for 30 min, respectively. All of the data presented in the work were measured using a HP4192A impedance analyzer with the frequency range of 5 Hz–13 MHz. The samples were connected to the analyzer with the accessory 16048B test lead, which is a carefully designed unit with four coaxial cables. A pair of Helmholtz coils (30 cm in diameter) was used to generate an applied dc magnetic field in the range of
0921-5093/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 5 0 9 3 ( 0 0 ) 0 1 6 0 1 - 4
S.X. Zhou et al. / Materials Science and Engineering A304–306 (2001) 954–956
955
0–70 Oe. The coils are so placed that the applied field is perpendicular to the earth magnetic field. 3. Results and discussion Fig. 1 shows the frequency dependence of the impedance ratios |[Z(65 Oe) − Z(0)]/Z(0)| for the as-cast sample and samples annealed at temperatures of 300 350, 400, and 450◦ C for 30 min, respectively. Here Z(65 Oe) and Z(0) represent the impedance at dc magnetic field of H = 65 and 0 Oe. It can be seen that the GMI value of the as-cast wire is larger than those of the annealed wires. There exists an optimum frequency where the value of |[Z(65 Oe) − Z(0)]/Z(0)| has a maximum for all samples investigated. The maximum phenomenon is evident for annealed wires, whereas the peak phenomenon for the as-cast wire is too small to be observed. The frequency (fmax ) of annealed wires where the maximum GMI value occurs, is higher than that of the as-cast wire. The frequency (fmax ) for the as-cast wire is 0.3 MHz and is about 1 MHz for the wire annealed at 350◦ C. It is worthy to note that the maximum GMI value, GMI(Z)max is 73% for the as-cast wire and is 71% for the wire annealed at 350◦ C. Below 1 MHz, the GMI(Z) value of the as-cast wire is larger than those of the wires annealed at different temperatures. Above 1 MHz, the GMI(Z) value of the wire annealed at 350◦ C is the largest in all samples investigated. Fig. 2 shows the annealing temperature dependence of GMI(Z)max = |[Z(65 Oe)−Z(0)]/Z(0)|max measured from all annealed samples. It is evident that GMI(Z)max increases with increasing annealing temperature up to a maximum and then drops after 350◦ C. This implies that the annealing temperature should not be too high. Otherwise the samples tend to be crystallized and GMI value drops sharply. Such behavior is different from the case of FeCuNbSiB wires [8]. The largest GMI comes from the nanocrystalline state for FeCuNbSiB wires. Fig. 3 shows the dc field dependence of GMI value [Z(H ) − Z(0)]/Z(0) for the as-cast wire. It can be seen
Fig. 1. Frequency dependence of the GMI value of the as-cast and annealed amorphous wires.
Fig. 2. Dependence of the GMI value of the amorphous wires on annealing temperatures.
that at a low frequency of 0.1 MHz the GMI value decreases with increasing dc magnetic field. At high frequency range such as 1 and 12 MHz, there exists a peak phenomenon in the dc field dependence of GMI. Such peak phenomenon is associated with the circumferential anisotropy. The circumferential anisotropy field HK corresponds to the peak-field HP , where the peak occurs and varies with ac frequency [4]. The value of HK is the function of the ac frequency (f). It can be seen from Fig. 3 that HK (1 MHz) < H K (12 MHz). It has also been found that at high frequencies the skin effect becomes pronounced and the total wire impedance depends on the circumferential permeability through the penetration depth. There are two different kinds of contributions to the effective permeability [4]: (1) domain wall movement and (2) magnetization rotation. At low frequencies when the external field Hex is lower than HK the mechanism of domain wall movement dominates the effective permeability. With increasing frequency the rotation permeability becomes important even at H ex < H K since the wall movement becomes more and more damped. The longitudinal external field stimulates the rotational process while H ex < H K and the corresponding permeability has a
Fig. 3. Dependence of GMI value of the as-cast amorphous wire on dc applied field.
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S.X. Zhou et al. / Materials Science and Engineering A304–306 (2001) 954–956
Fig. 6. Dependence of magneto-reactance of the as-cast amorphous wire on dc applied field at the frequencies of 0.1 and 12 MHz. Fig. 4. Dependence of GMI value of the amorphous wires annealed at 350◦ C on dc applied field.
maximum at H ex = H K . The dc field dependence of GMI value with different ac frequencies for the wire annealed at 350◦ C is shown in Fig. 4. The peak phenomenon can be found at 12 MHz but not at 1 MHz. Compared with the case of the as-cast wire the circumferential anisotropy field HK changes very little which is about 8 Oe. In order to give more information on GMI for Fe4.5 Co67.5 Nb0.5 Mn0.5 Si12 B15 amorphous wires, the dc field dependence of the magneto-resistance [R(H ) − R(0)]/R(0) and magneto-reactance [X(H ) − X(0)]/X(0) for the as-cast sample are investigated as shown in Figs. 5 and 6. It can be seen from Fig. 5 that with increasing dc field the value of magneto-resistance ratio [R(H ) − R(0)]/R(0) decreases monotonously at the frequency of 0.1 MHz, whereas in the case of frequency, f = 12 MHz, the magneto-resistance ratio increases firstly undergoes a peak in positive value and finally drops again. The peak value of [R(H ) − R(0)]/R(0) at 12 MHz reaches about 60%. It is evident from Fig. 6 that with increasing dc field the magneto-reactance ratio, [X(H ) − X(0)]/X(0), exhibits the peak-phenomenon in both 12 and 0.1 MHz, and the peak field HP at 12 MHz
is larger than that at 0.1 MHz. It should be noticed that in Fig. 3 no evident peak of GMI is observed at the frequency of 0.1 MHz with applied field. However, from the curve of magneto-reactance versus applied field in Fig. 6, a well-defined peak is observed at the frequency of 0.1 MHz. This may be because of the value of reactance for the as-cast wires is much less than that of resistance at low frequency range [6].
4. Conclusions The following conclusions may be drawn from the investigations. 1. There exists an optimum frequency where the GMI shows a maximum for all samples investigated, and the maximum GMI values of the as-cast wire and the wire annealed at 350◦ C are 73 and 71%, respectively. 2. GMI effect for the as-cast wire in the frequency range <1 MHz is much higher than those for the annealed samples, and in the case of frequency range >1 MHz GMI effect is better than that of the as-cast state. 3. GMI(Z)max shows a maximum with annealing temperature, the optimum annealing temperature is 350◦ C in the study. References
Fig. 5. Dependence of magneto-resistance of the as-cast amorphous wire on dc applied field at the frequencies of 0.1 and 12 MHz.
[1] K. Mohri, K. Kawashima, T. Kohzawa, Y. Yoshida, L.V. Panina, IEEE Trans. Magn. 28 (1992) 3150. [2] K. Mohri, K. Kawashima, T. Kohzawa, Y. Yoshida, IFEE Trans. Magn. 29 (1993) 1245. [3] R.S. Beach, A.E. Berkowitz, Appl. Phys. Lett. 64 (1994) 3682. [4] L.V. Panina, K. Mohri, T. Uchiyama, M. Noda, IEFE Trans. Magn. 31 (1995) 1249. [5] D. Atkinson, P.T. Squire, IEEE Trans. Magn. 33 (1997) 3364. [6] S.X. Zhou, J.F. Hu, Met. Func. Mater. 5 (1998) 19 (in Chinese). [7] J.F. Hu, S.X. Zhou, Met. Func. Mater. 6 (1999) 21 (in Chinese). [8] H. Chiriac, T.A. Ovari, C.S. Marinescu, J. Appl. Phys. 83 (1998) 6584.