DSpace at VNU: Giant magnetoimpedance effect in Co70Fe5Si15B10 and Co70Fe5Si15Nb2.2Cu0.8B7 ribbons

Home Search Collections Journals About Contact us My IOPscience Giant Magnetoimpedance Effect in Co70Fe5Si15B10 and Co70Fe5Si15Nb2.2Cu0.8B7 Ribbons This content has been downloaded from IOPscience Please scroll down to see the full text 2003 Jpn J Appl Phys 42 5571 (http://iopscience.iop.org/1347-4065/42/9R/5571) View the table of contents for this issue, or go to the journal homepage for more Download details: IP Address: 128.192.114.19 This content was downloaded on 02/09/2015 at 04:35 Please note that terms and conditions apply Jpn J Appl Phys Vol 42 (2003) pp 5571–5574 Part 1, No 9A, September 2003 #2003 The Japan Society of Applied Physics Giant Magnetoimpedance Effect in Co70 Fe5 Si15 B10 and Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 Ribbons Manh-Huong PHAN, Yong-Seok K IM, Nguyen Xuan C HIEN1 , Seong-Cho Y UÃ, Heebok L EE2 and Nguyen C HAU1 Department of Physics, Chungbuk National University, Cheongju 361-763, Korea Center for Materials Science, National University of Hanoi, 334 Nguyen Trai, Hanoi, Vietnam Department of Physics Education, Kongju National University, Kongju 314-701, Korea (Received January 27, 2003; accepted for publication May 22, 2003) Giant magnetoimpedance (GMI) effect has been observed in Co70 Fe5 Si15 B10 and Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 melt-spun amorphous ribbons The magnetoimpedance (MI) of these samples has been studied up to a frequency of 10 MHz and varying a dc magnetic field (Hdc ) within 150 Oe A maximum change of 89% in MI has been observed for Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 composition around a frequency of 3.1 MHz Substitution of Cu and Nb for B in an initial Co70 Fe5 Si15 B10 composition forming the Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 composition not only favors the GMI effect but also gives rise to the sensitivity of the magnetic response ($18%/Oe), which is very beneficial for magnetic sensors applications The GMI effect for both samples annealed at 550 K is further enhanced due to the presence of the ultrasoft magnetic materials, compared to their as-quenched samples [DOI: 10.1143/JJAP.42.5571] KEYWORDS: magnetoimpedance effect, magnetic sensing sensors, Co-based amorphous alloys, proper heat treatments Introduction Recently, a giant magnetoimpedance (GMI) effect, discovered in amorphous magnetic materials, has generated growing interests among researchers and manufacturers because of its practical potential for magnetic sensing and recording applications.1–4) Among amorphous alloys, Co- or Co–Fe-based amorphous wires and ribbons with vanishing magnetostriction show a giant magnetoimpedance change.2–7) The GMI effect is demonstrated to arise from a combination of a skin effect and strong field dependence of the circumferential magnetic permeability associated with circular domain wall movements As an ac current I ẳ I0 expj!tị is applied to such materials, their impedance Z ẳ R ỵ j!L changes sensitively with changes in the biasing dc magnetic field, Hdc At low frequencies ($kHz), the ac current just generates a circumferential magnetic field This time varying magnetic field changes the transverse component of magnetization When the biasing dc magnetic field is applied along the wire (or ribbon) axis, the effective magnetic field on the wire (or ribbon) changes Consequently, both the transverse component of magnetization and the transverse permeability are varied thus leading to a large change in the magneto-inductive effect At high frequencies, the GMI effect can be interpreted in terms of the dc magnetic field dependence of impedance as a result of the transverse magnetization with respect to the ac current direction flowing through the sample and the skin effect due to this ac current.1) Because the ac current tends to concentrate near the surface of a conductor, as frequency increases, the impedance responds to the current distribution which depends not only on the shape of the conductor and frequency but also on the transverse permeability with respect to the applied current In such a magnetic material, the transverse permeability ? effects on the magnetic penetration depth m ; m ẳ =f ? ị1=2 , where f is the frequency and  is the electrical resistivity It is expected that with increasing frequency, the impedance in case of the skin effect a=m ) is proportional to ðf ? Þ1=2 Because the external dc magnetic field is a hard axis field with respect to the circumferential anisotropy, the magnetic field applied along the ribbon axis will suppress transverse magnetization processes by domain wall movements at low frequencies or the motion of localized magnetic moments at high frequencies In other words, the transverse permeability decreases rapidly as the external dc magnetic field is applied, which in turn causes a giant magnetoimpedance change, i.e., the GMI effect In a series of recent works,7–10) moreover, it has been demonstrated that proper heat treatments on amorphous ribbons led to a nanocrystalline structure with ultra-high permeability (>106 ) and thus further enhanced the GMI effect Under these cases, the high permeability values have been believed to be associated with a transverse magnetic domain structure perpendicular to the long axis of the sample, in which the reversible magnetization rotation is a dominant mechanism for changes in the magnetic state.9,10) In this article, we report on the GMI effect in the Co70 Fe5 Si15 B10 and Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 melt-spun amorphous ribbons The GMI effect further enhanced in the nanocrystalline samples due to thermal treatment is also reported Experimental The Co70 Fe5 Si15 B10 and Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 ribbons with mm in width and 20 mm in thickness were prepared by rapid quenching from the melt The samples were annealed in a conventional furnace at 550 K for one hour, in vacuum Amorphous and nanocrystalline states were confirmed by X-ray diffractometry (XRD) The hysteresis loops were performed using a vibrating sample magnetometer (VSM) The resistivity measurements for both samples were carried out with the four-probe method The obtained resistivity values are  ¼ 1:1  10À5 m and 0:75  10À5 m for Co70 Fe5 Si15 B10 and Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 compositions, respectively The GMI measurements were carried out along the ribbon axis with the longitudinal applied magnetic field The samples were cut out about 15 mm in length for all the GMI measurements A schematic diagram of the GMI measurement system has been described in details elsewhere.3) A computer-controlled RF signal generator with its power amplifier was connected to the sample in a series with resistors for monitoring the driving ac current An ac current and a voltage across the à Corresponding author E-mail address: scyu@chungbuk.ac.kr 5571 5572 Jpn J Appl Phys Vol 42 (2003) Pt 1, No 9A sample were measured by digital multimeters (DMM) with RF/V probes for calculating the impedance The external dc field applied by a solenoid can be swept through the entire cycle equally divided by 800 intervals from À150 to 150 Oe The frequency of the ac current was varied from to 10 MHz while its magnitude was kept constantly at 10 mA Results and Discussions The magnetoimpedance ratio (MIR) can be dened as MIR%ị ẳ jZHị=ZHmax ịj, where Hmax is the external magnetic field sufficient for saturating the magnetoimpedance and equals to 150 Oe for the present work Similarly, the longitudinal permeability ratio (LPR) measured as a function of the external magnetic field can be also defined as LPR%ị ẳ jHị=Hmax ịj Regarded to the GMI effect, recent studies4,7,9–11) have proposed that change in the magnetoimpedance is closely related to that of the longitudinal permeability It means that evaluations for the GMI effect in amorphous soft magnetic alloys can be realized either by the MIR measurements or the LPR measurements As shown in Fig 1, the MIR curves, measured at frequencies up to f ¼ 4:1 MHz, for both Co70 Fe5 Si15 B10 and Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 compositions have a single peak at zero external magnetic field At the frequency of 3.1 MHz, the maximum MIR magnitude is $55% and $89% for Co70 Fe5 Si15 B10 and Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 composi- 60 50 (a) 1.1 MHz 2.1 MHz 3.1 MHz 4.1 MHz 40 30 20 MIR (%) 10 90 1.1 MHz 2.1 MHz 3.1 MHz 4.1 MHz (b) 75 60 45 30 15 -150 -100 -50 50 100 150 Field (Oe) Fig The MIR curves measured as a function of the external magnetic field at various frequencies (1.1–4.1 MHz) for the as-quenched amorphous samples: (a) Co70 Fe5 Si15 B10 composition and (b) Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 composition M.-H P HAN et al tions, respectively A higher MIR value for Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 composition, measured at f ¼ 3:1 MHz, can be attributed to the presence of its special domain structure containing transverse domains formed by a magnetomechanical coupling between internal stress and magnetostriction.9–11) In the present case, partial substitution of Cu and Nb for B in the initial Co70 Fe5 Si15 B10 composition seems to favor the formation of a transverse domains structure, because of the presence of Cu and Nb allowing the formation of well-differentiated microstructures.13) Thereby, higher transverse permeability value for Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 than for Co70 Fe5 Si15 B10 can be expected This results in a larger MIR value for Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 composition In addition, the obtained maximum MIR values for Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 composition are higher than those for Co70 Fe5 Si15 B10 composition at all measured frequencies, indicative of a favorably formed transverse domain structure in Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 alloy rather than in Co70 Fe5 Si15 B10 alloy Another reason that also led to the difference in MIR values of the above two compositions is the difference in their electrical resistivity As reported in ref 1, the higher the electrical resistivity of amorphous alloy, the lower the obtained MIR value is In the present work, the resistivity is  ¼ 1:1  10À5 m for Co70 Fe5 Si15 B10 composition, and is higher than  ¼ 0:75  10À5 m for Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 composition Because of that, the higher MIR values obtained for Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 composition can be understandable This is consistent with the results that had been reported in Ref It is clear that, from Fig 1(b), there is a small full width at haft maximum (FWHM) in MIR curves for Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 composition, which indicates high sensitivity of the MIR to magnetic field The Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 , GMI sensitive material, has high sensitivity of 17–18%/Oe for a current driving frequency of f ¼ 3:1 MHz It is interesting to note that the high sensitivity of the magnetic response almost remains at high frequencies, meanwhile it had not been often found in the other materials.1,3,11–16) Thus the Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 material is, at present, a very promising candidate for magnetic sensors applications Compared to Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 composition, the larger FWHM of MIR curves for Co70 Fe5 Si15 B10 composition, corresponding to the magnetic response sensitivity of $1%/Oe at f ¼ 3:1 MHz, was found Moreover, this broadening was also clarified by the hysteresis loops observations; the local magnetic anisotropy along the ribbon axis in the Co70 Fe5 Si15 B10 composition was much larger than that in the Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 composition It is the local anisotropy that considerably reduced the transverse magnetization associated with the transverse magnetic permeability and thus led to the broadening in the MIR curves and the smaller value of MIR for Co70 Fe5 Si15 B10 composition A similar behavior was also observed by the LPR curves (see Fig 2), where the FWHM of the LPR curves were much larger for Co70 Fe5 Si15 B10 composition than for Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 composition In order to further interpret the broadening of the LPR curves, a model for the transverse biased permeability in thick ferromagnetic films can be adopted.17) According to this model, it is the eddy current damping and the ripple field HR incorporating with the Jpn J Appl Phys Vol 42 (2003) Pt 1, No 9A 14 (a) 10 LPR (%) 75 60 45 30 15 120 1.1 MHz 2.1 MHz 3.1 MHz 4.1 MHz 5.1 MHz 6.1 MHz (b) 100 80 Co70Fe5Si15B10 Co70Fe5Si15Nb2.2Cu0.8B7 90 140 5573 105 1.1 MHz 2.1 MHz 3.1 MHz 4.1 MHz 5.1 MHz 6.1 MHz MIRmax (%) 12 M.-H P HAN et al Frequency (MHz) Fig The maximum of MIR versus frequency for Co70 Fe5 Si15 B10 and Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 as-quenched amorphous samples 60 40 20 -150 -100 -50 50 100 150 in a nanocrystalline phase It indicates that soft magnetic properties of the as-quenched amorphous samples seemed to be further improved by annealing at 550 K As shown in Fig 4, the LPR magnitude and the FWHM of LPR curves for the 550 K-annealed samples did change much, as compared to the as-quenched samples (see Fig 2) It is worthy that H (Oe) Fig The LPR curves measured as a function of the external magnetic field at various frequencies (1.1–6.1 MHz) for the as-quenched amorphous samples: (a) Co70 Fe5 Si15 B10 composition and (b) Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 composition 70 60 (a) 1.1 MHz 2.1 MHz 3.1 MHz 4.1 MHz 5.1 MHz 6.1 MHz (b) 1.1 MHz 2.1 MHz 3.1 MHz 4.1 MHz 5.1 MHz 6.1 MHz 50 40 30 20 10 LPR (%) anisotropy HK that give rise to the peak of permeability in an external field as well as the broadening of the LPR curves at high frequencies With the above indications, we can conclude that the evaluation for the GMI effect in amorphous soft magnetic alloys either through the MIR measurements or the LPR measurements is valid As can be seen from Fig 3, frequency dependences of the maximum MIR for both compositions show that at first the MIR increased as frequency increased up to f ¼ 3:1 MHz and then reduced at higher frequencies It should be noted that, at frequencies below 1.1 MHz (the ribbon thickness, a < ), the maximum MIR value was not very large because of the contribution of the induced magneto-inductive voltage to magnetoimpedance At 1.1 MHz f 3.1 MHz (a % ), in the case of skin effect, the higher MI values are reported Beyond f ¼ 3:1 MHz, the maximum MIR decreased with increasing frequency The reason here is that in the frequency region (3.1 MHz f ), domain wall displacements were strongly damped owing to Eddy currents and thus contributed less to the transverse permeability, which in turn caused a small magnetoimpedance change and hence, the small value of MIR In order to investigate annealing effects on the GMI profiles, we have carried out the LPR measurements for 550 K-annealed Co70 Fe5 Si15 B10 and Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 ribbons Prior to the LPR measurements, from XRD patterns it is confirmed that the annealed ribbons were 200 150 100 50 -150 -100 -50 50 100 150 H (Oe) Fig The LPR curves measured as a function of the external magnetic field at various frequencies (1.1–6.1 MHz) for the 550 K annealed samples: (a) Co70 Fe5 Si15 B10 composition and (b) Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 composition 5574 Jpn J Appl Phys Vol 42 (2003) Pt 1, No 9A Co70Fe5Si15B10 (as-quenched) Co70Fe5Si15Nb2.2Cu0.8B7 (as-quenched) Co70Fe5Si15B10 (annealed at 550 K) Co70Fe5Si15Nb2.2Cu0.8B7 (annealed at 550 K) 200 LPRmax (%) M.-H P HAN et al 160 120 80 40 Frequency (MHz) Fig The maximum of LPR versus frequency for the as-quenched and 550 K-annealed samples Conclusions and The GMI effect in Co70 Fe5 Si15 B10 Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 melt-spun amorphous ribbons have been studied A maximum change of 89% in MI has been observed for the Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 composition around f ¼ 3:1 MHz Substitution of Cu and Nb for B in the initial Co70 Fe5 Si15 B10 composition forming the Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 composition not only favors the GMI effect but also provides higher sensitivity of the magnetic response (17–18%/Oe at f ¼ 3:1 MHz), which is very beneficial for magnetic sensors applications The GMI effect for both samples annealed at 550 K is further enhanced by the presence of the ultra-soft magnetic materials, as compared to the as-quenched samples The difference in the electrical resistivity and the existence of specific domain structures in the amorphous alloys could be originated from their different MIR values Acknowledgements after annealing, changes in the LPR magnitude and the FWHM of LPR curves for Co70 Fe5 Si15 B10 composition drastically occurred, which is connected to a considerable reduction in the local magnetic anisotropy and magnetostriction.12) Moreover, smaller value of the magnetic anisotropy for the 550 K-annealed Co70 Fe5 Si15 B10 sample than its as-quenched amorphous samples was also verified by the hysteresis loops measurements More briefly, it is the improved soft magnetic properties of the Co70 Fe5 Si15 B10 sample through heat treatment that led to an increase in the MIR and reductions in the FWHM of MIR curves for this sample In Fig 5, the maximum value of LPR versus frequency for the as-quenched and 550 K-annealed samples are presented It is obvious that in a region of frequencies (1.1–6.1 MHz), LPRmax (%) values calculated for the 550 Kannealed samples were higher than those for their asquenched samples We should recall that the higher the longitudinal permeability value, the larger the obtained MIR value is.9,10) Thus, the 550 K-annealed Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 sample here is expected to exhibit the higher value of MIR Additionally, LPRmax (%) changes as a decreasing function of the measured frequency can be explained as follow: in the frequency region (1.1–6.1 MHz), the longitudinal permeability resulting from rotational magnetization decreased with increasing frequency, thus leading to the corresponding reduction of LPRmax (%) It should be emphasized that the GMI effect is further enhanced in both Co70 Fe5 Si15 B10 and Co70 Fe5 Si15 Nb2:2 Cu0:8 B7 melt-spun amorphous ribbons by annealing at 550 K One of the authors (M H Phan) would like to thank Professor Sunk Kun Oh for helpful discussions Research at Korea was supported by the Korea Research Foundation Grant (KRF-2001-005-D20010) 1) L V Panina and K Mohri: Appl Phys Lett 65 (1994) 1189 2) L V Panina and K Mohri: J Magn Soc Jpn 19 (1995) 265 3) Y K Kim, W S Cho, T K Kim, C O Kim and H B Lee: J Appl Phys 83 (1998) 6575 4) H B Lee, K J Lee, Y K Kim, T K Kim, C O Kim 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Appl Phys 73 (1993) 5995  ... amorphous wires and ribbons with vanishing magnetostriction show a giant magnetoimpedance change.2–7) The GMI effect is demonstrated to arise from a combination of a skin effect and strong field... GMI effect, recent studies4,7,9–11) have proposed that change in the magnetoimpedance is closely related to that of the longitudinal permeability It means that evaluations for the GMI effect in. .. KEYWORDS: magnetoimpedance effect, magnetic sensing sensors, Co-based amorphous alloys, proper heat treatments Introduction Recently, a giant magnetoimpedance (GMI) effect, discovered in amorphous