- Email: [email protected]
Fe70Cr10B20 metallic glass as a new candidate for nuclei of stress and magnetic field sensors
Sensors and Actuators A 129 (2006) 66–68
Fe70Cr10B20 metallic glass as a new candidate for nuclei of stress and magnetic field sensors M.L. S´anchez, J.D. Santos ∗ , M.J. P´erez, J. Olivera, V.M. Prida, P. Gorria, B. Hernando Departamento de F´ısica, Universidad de Oviedo, Calvo Sotelo s/n, 33007 Oviedo, Spain Received 5 July 2004; received in revised form 26 November 2004; accepted 19 September 2005 Available online 20 December 2005
Abstract In this work, we present some results concerning the magnetoimpedance and stress impedance in Fe70 Cr10 B20 ribbons. A high response is obtained at low values of the applied field and stress, making it possible to develop sensitive devices that could detect small values of magnetic fields and/or tensile stresses. Sensitivities, per unit length, to the applied tensile stress of up to 14%/m MPa are measured under tensile stresses of 40 MPa in the case of the annealed sample. © 2005 Elsevier B.V. All rights reserved. Keywords: Amorphous ribbons; Magnetoimpedance; Stress impedance; Magnetic sensors
1. Introduction
2. Experimental details
Diverse ferromagnetic amorphous materials show large responses of the electrical impedance under the influence of external magnetic fields and/or mechanical stresses. This feature makes these alloys good candidates for the design and development of new micro-devices, such as magnetic field sensors. Materials with low value of the magnetostriction constant provide a good response of the impedance when a magnetic field is applied. On the other hand, a high response under the application of tensile stresses can be obtained, without the application of any bias magnetic field, in materials with larger value of the magnetostriction. These changes have been used to study the stress response of impedance in amorphous ribbons [1]. The addition of Cr to FeB-based metallic glasses changes the mechanical and magnetic properties of such materials [2,3]. The effect of tensile stress has been studied before in Co-rich and Fe-rich ribbons containing some Cr [4,5]. In this work, we study the impedance response to applied magnetic fields and tensile stresses in order to use Fe70 Cr10 B20 ribbons as a nucleus of magnetic field or stress sensors.
The Fe70 Cr10 B20 ribbons, with a cross section of 5 mm × 24 m, have been obtained in our laboratory by means of melt spinning technique. The measurements were carried out in the as quenched samples, and after being stress relaxed at 300 ◦ C during 1 h, far from the crystallization temperature (above 450 ◦ C). Differential scanning calorimetry has been used in order to follow the crystallization process, while the value of the Curie temperature (around 100 ◦ C) has been obtained from magnetization versus temperature measurements. The values of the saturation magnetostriction coefficient, obtained by the SAMR technique, for the as quenched (aq) and stress relaxed (sr) samples are +3.5 × 10−6 and +4 × 10−6 , respectively. These values are large enough to produce a magnetization change when a tensile stress is applied. A saturation polarization of around 0.5 T was estimated from the hysteresis loops, obtained by a conventional induction technique at room temperature. The samples were carefully clamped, and a bias magnetic field or a tensile stress was applied in order to measure the magnetoimpedance or the stress impedance.
3. Results and discussion ∗
Corresponding author. Tel.: +34 98 510 3307; fax: +34 98 510 3324. E-mail address: [email protected] (J.D. Santos).
0924-4247/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2005.09.049
The stress impedance (SI) and magnetoimpedance (MI) are calculated with respect to the maximum applied stress or torsion,
M.L. S´anchez et al. / Sensors and Actuators A 129 (2006) 66–68
Fig. 1. Magnetoimpedance and stress impedance spectra for the as quenched ribbon. The drive current amplitude was 20 mA rms.
in the following way: Z(σ) − Z(σmax ) Zσ (%) = 100 × Z Z(σmax )
(1)
Z(H) − Z(Hmax ) ZH (%) = 100 × Z Z(Hmax )
(2)
where σ max = 40 MPa and Hmax = 100 Oe are the maximum applied stress and field, respectively. We use impedance per unit length in all cases. The sensitivities to the applied magnetic field or stress can be calculated from: 2 ZP s= (3) F Z max where F is the full width at half maximum and P refers to the magnetic field or applied stress. The SI and MI spectra show similar results for all the samples. A maximum appears at a drive current frequency of 1 MHz in all cases. The further application of magnetic fields or tensile stresses was performed at this frequency. This behaviour is shown in Fig. 1 for the case of the as quenched sample. The ribbons annealed at 300 ◦ C (sr) have a similar behaviour. It has to be noted that the effect of a magnetic field of 100 Oe is as large as the effect of the 40 MPa tensile stress. Fig. 2 shows the field dependence of the magnetoimpedance, calculated as in Eq. (1), for the as quenched and the sr samples, per unit length. The MI was measured with no applied tensile stress and with an applied tensile stress of 40 MPa. The drive current amplitude was 20 mA, and its frequency was 1 MHz. In all cases the MI decreases strongly for the lower values of the magnetic field. The sensitivities to the applied magnetic field can be obtained from Eq. (3), and are 8%/Oe m, and 4%/Oe m, for the as quenched and sr samples, respectively, in the case of no applied tensile stress. Several parameters influence the MI response of soft magnetic materials, making the magnetic field sensitivity higher for the as quenched sample. One of these parameters is the magnetostriction coefficient. The as quenched sample has a somewhat lower λs , and therefore a softer magnetic behaviour, although
67
Fig. 2. Magnetoimpedance dependence on bias magnetic field for the as quenched and stress relaxated ribbons with no applied stress and with an applied tensile stress of 40 MPa.
hysteresis loops show the enhancement of the permeability in the sr sample respect to the as quenched ribbon. There is a competition between the influence of a lower magnetostriction and lower permeability that would decrease MI. The sensitivities to the magnetic field when a 40 MPa tensile stress is applied, are 2.6%/Oe m and 4.5%/Oe m, for the aq and sr samples, respectively. The curve is wider for the aq sample, but the maximum at H = 0 Oe increases for the sr sample. The magnetostriction constant decreases with the application of tensile stresses. When tensile stress is applied to ribbons with a positive magnetostriction coefficient, a longitudinal magnetic anisotropy developes, increasing the value of magnetic permeability. The different changes of both parameters in the two types of ribbon can explain the decrease of sensitivity in the aq sample, and the small increase in the sr sample, with respect to the case of no applied stress. In Fig. 3, the tensile stress dependence of stress impedance is shown for both types of sample, at a drive current frequency of 1 MHz. The stress impedance shows a strong decrease in all the samples. The decrease is particularly strong at low values of stress for the sr sample. The increase of the magnetostriction coefficient with the annealing treatment explains the higher response of this ribbon to the applied stress. The high value of SI in the sr sample is also understood by the enhancement
Fig. 3. Stress impedance as a function of the applied tensile stress for the as quenched and the stress relaxated samples at a drive current frequency of 1 MHz.
68
M.L. S´anchez et al. / Sensors and Actuators A 129 (2006) 66–68
of magnetic permeability that takes place in this sample due to the relaxation treatment, and that can be observed in the hysteresis loops. The effect of the relaxation annealing can also be seen in Bitter patterns of the surface domain structure that show a reduction of the zones with perpendicular anisotropy. The sensitivities to the applied stress calculated as in Eq. (3) are 3%/MPa m and 14%/MPa m for the aq and the sr samples, respectively, showing the largest response of the sr sample. From these results, we can conclude that the interest of this FeCrB glassy alloy lies in the high MI sensitivity at low values for the magnetic field and mechanical stress. Hence, they could be good candidates to be used as stress and/or magnetic field sensors.
Acknowledgement We acknowledge CICYT for finantial support under proyect no. MAT2003 – 06942. References [1] M. Tejedor, B. Hernando, M.L. S´anchez, V.M. Prida, M. V´azquez, Sens. Actuators A 81 (2000) 98. [2] J.A. Verduzco, I. Betancourt, F. Saavedra, E. Reynoso, J. Non-Cryst. Solids 329 (2003) 163. [3] U. G¨untzel, K. Westerholt, Phys. Rev. B 41 (1990) 740. [4] I. Mihalca, A. Ercuta, C. Ionascu, Sens. Actuators A 106 (2003) 61. [5] L. Kraus, P. Svec, J. Bydzovskc¸y, J. Magn. Magn. Mater. 242 (2002) 241.
Fe70Cr10B20 metallic glass as a new candidate for nuclei of stress and magnetic field sensors M.L. S´anchez, J.D. Santos ∗ , M.J. P´erez, J. Olivera, V.M. Prida, P. Gorria, B. Hernando Departamento de F´ısica, Universidad de Oviedo, Calvo Sotelo s/n, 33007 Oviedo, Spain Received 5 July 2004; received in revised form 26 November 2004; accepted 19 September 2005 Available online 20 December 2005
Abstract In this work, we present some results concerning the magnetoimpedance and stress impedance in Fe70 Cr10 B20 ribbons. A high response is obtained at low values of the applied field and stress, making it possible to develop sensitive devices that could detect small values of magnetic fields and/or tensile stresses. Sensitivities, per unit length, to the applied tensile stress of up to 14%/m MPa are measured under tensile stresses of 40 MPa in the case of the annealed sample. © 2005 Elsevier B.V. All rights reserved. Keywords: Amorphous ribbons; Magnetoimpedance; Stress impedance; Magnetic sensors
1. Introduction
2. Experimental details
Diverse ferromagnetic amorphous materials show large responses of the electrical impedance under the influence of external magnetic fields and/or mechanical stresses. This feature makes these alloys good candidates for the design and development of new micro-devices, such as magnetic field sensors. Materials with low value of the magnetostriction constant provide a good response of the impedance when a magnetic field is applied. On the other hand, a high response under the application of tensile stresses can be obtained, without the application of any bias magnetic field, in materials with larger value of the magnetostriction. These changes have been used to study the stress response of impedance in amorphous ribbons [1]. The addition of Cr to FeB-based metallic glasses changes the mechanical and magnetic properties of such materials [2,3]. The effect of tensile stress has been studied before in Co-rich and Fe-rich ribbons containing some Cr [4,5]. In this work, we study the impedance response to applied magnetic fields and tensile stresses in order to use Fe70 Cr10 B20 ribbons as a nucleus of magnetic field or stress sensors.
The Fe70 Cr10 B20 ribbons, with a cross section of 5 mm × 24 m, have been obtained in our laboratory by means of melt spinning technique. The measurements were carried out in the as quenched samples, and after being stress relaxed at 300 ◦ C during 1 h, far from the crystallization temperature (above 450 ◦ C). Differential scanning calorimetry has been used in order to follow the crystallization process, while the value of the Curie temperature (around 100 ◦ C) has been obtained from magnetization versus temperature measurements. The values of the saturation magnetostriction coefficient, obtained by the SAMR technique, for the as quenched (aq) and stress relaxed (sr) samples are +3.5 × 10−6 and +4 × 10−6 , respectively. These values are large enough to produce a magnetization change when a tensile stress is applied. A saturation polarization of around 0.5 T was estimated from the hysteresis loops, obtained by a conventional induction technique at room temperature. The samples were carefully clamped, and a bias magnetic field or a tensile stress was applied in order to measure the magnetoimpedance or the stress impedance.
3. Results and discussion ∗
Corresponding author. Tel.: +34 98 510 3307; fax: +34 98 510 3324. E-mail address: [email protected] (J.D. Santos).
0924-4247/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.sna.2005.09.049
The stress impedance (SI) and magnetoimpedance (MI) are calculated with respect to the maximum applied stress or torsion,
M.L. S´anchez et al. / Sensors and Actuators A 129 (2006) 66–68
Fig. 1. Magnetoimpedance and stress impedance spectra for the as quenched ribbon. The drive current amplitude was 20 mA rms.
in the following way: Z(σ) − Z(σmax ) Zσ (%) = 100 × Z Z(σmax )
(1)
Z(H) − Z(Hmax ) ZH (%) = 100 × Z Z(Hmax )
(2)
where σ max = 40 MPa and Hmax = 100 Oe are the maximum applied stress and field, respectively. We use impedance per unit length in all cases. The sensitivities to the applied magnetic field or stress can be calculated from: 2 ZP s= (3) F Z max where F is the full width at half maximum and P refers to the magnetic field or applied stress. The SI and MI spectra show similar results for all the samples. A maximum appears at a drive current frequency of 1 MHz in all cases. The further application of magnetic fields or tensile stresses was performed at this frequency. This behaviour is shown in Fig. 1 for the case of the as quenched sample. The ribbons annealed at 300 ◦ C (sr) have a similar behaviour. It has to be noted that the effect of a magnetic field of 100 Oe is as large as the effect of the 40 MPa tensile stress. Fig. 2 shows the field dependence of the magnetoimpedance, calculated as in Eq. (1), for the as quenched and the sr samples, per unit length. The MI was measured with no applied tensile stress and with an applied tensile stress of 40 MPa. The drive current amplitude was 20 mA, and its frequency was 1 MHz. In all cases the MI decreases strongly for the lower values of the magnetic field. The sensitivities to the applied magnetic field can be obtained from Eq. (3), and are 8%/Oe m, and 4%/Oe m, for the as quenched and sr samples, respectively, in the case of no applied tensile stress. Several parameters influence the MI response of soft magnetic materials, making the magnetic field sensitivity higher for the as quenched sample. One of these parameters is the magnetostriction coefficient. The as quenched sample has a somewhat lower λs , and therefore a softer magnetic behaviour, although
67
Fig. 2. Magnetoimpedance dependence on bias magnetic field for the as quenched and stress relaxated ribbons with no applied stress and with an applied tensile stress of 40 MPa.
hysteresis loops show the enhancement of the permeability in the sr sample respect to the as quenched ribbon. There is a competition between the influence of a lower magnetostriction and lower permeability that would decrease MI. The sensitivities to the magnetic field when a 40 MPa tensile stress is applied, are 2.6%/Oe m and 4.5%/Oe m, for the aq and sr samples, respectively. The curve is wider for the aq sample, but the maximum at H = 0 Oe increases for the sr sample. The magnetostriction constant decreases with the application of tensile stresses. When tensile stress is applied to ribbons with a positive magnetostriction coefficient, a longitudinal magnetic anisotropy developes, increasing the value of magnetic permeability. The different changes of both parameters in the two types of ribbon can explain the decrease of sensitivity in the aq sample, and the small increase in the sr sample, with respect to the case of no applied stress. In Fig. 3, the tensile stress dependence of stress impedance is shown for both types of sample, at a drive current frequency of 1 MHz. The stress impedance shows a strong decrease in all the samples. The decrease is particularly strong at low values of stress for the sr sample. The increase of the magnetostriction coefficient with the annealing treatment explains the higher response of this ribbon to the applied stress. The high value of SI in the sr sample is also understood by the enhancement
Fig. 3. Stress impedance as a function of the applied tensile stress for the as quenched and the stress relaxated samples at a drive current frequency of 1 MHz.
68
M.L. S´anchez et al. / Sensors and Actuators A 129 (2006) 66–68
of magnetic permeability that takes place in this sample due to the relaxation treatment, and that can be observed in the hysteresis loops. The effect of the relaxation annealing can also be seen in Bitter patterns of the surface domain structure that show a reduction of the zones with perpendicular anisotropy. The sensitivities to the applied stress calculated as in Eq. (3) are 3%/MPa m and 14%/MPa m for the aq and the sr samples, respectively, showing the largest response of the sr sample. From these results, we can conclude that the interest of this FeCrB glassy alloy lies in the high MI sensitivity at low values for the magnetic field and mechanical stress. Hence, they could be good candidates to be used as stress and/or magnetic field sensors.
Acknowledgement We acknowledge CICYT for finantial support under proyect no. MAT2003 – 06942. References [1] M. Tejedor, B. Hernando, M.L. S´anchez, V.M. Prida, M. V´azquez, Sens. Actuators A 81 (2000) 98. [2] J.A. Verduzco, I. Betancourt, F. Saavedra, E. Reynoso, J. Non-Cryst. Solids 329 (2003) 163. [3] U. G¨untzel, K. Westerholt, Phys. Rev. B 41 (1990) 740. [4] I. Mihalca, A. Ercuta, C. Ionascu, Sens. Actuators A 106 (2003) 61. [5] L. Kraus, P. Svec, J. Bydzovskc¸y, J. Magn. Magn. Mater. 242 (2002) 241.