Asymmetric Giant Magnetoimpedance Research Articles

Asymmetric magnetoimpedance effect and dipolar interactions of FINEMET/SiO2/FePd composite ribbons

The dipolar interactions are investigated through the asymmetric magneto-impedance in FINEMET/SiO2/FePd composite ribbons. The interface between the hard (FePd layer) phase and soft (FINEMET ribbon) phase is coherent by SiO2 layer in FINEMET/SiO2/FePd composite ribbons, which effectively induces dipolar interactions. The contribution of dipolar interaction to the bias field (H b) by asymmetrical giant magneto-impedance and magnetic properties is analyzed. The results show that H b response decreases with the increase of the SiO2 layer thickness, indicating that the linear region near-zero field can be tuned by the thickness of SiO2 layer. These results allow the GMI ratio (58%) and characteristic frequency (500 kHz) to be optimized. The transverse and longitudinal magnetic domain structures of FINEMET ribbon and FePd film are confirmed, respectively. The composite ribbons with high GMI ratio and low frequency can be applied to linear magnetic sensors.

Enhanced asymmetric giant magneto-impedance effect and linearity in sandwich FePd/FINEMET/FePd composite ribbons

The FePd/FINEMET/FePd composite ribbons with sandwich structure were designed by magnetron sputtering. The morphology, magnetic properties and asymmetric giant magneto-impedance (AGMI) effect of FePd/FINEMET/FePd composite ribbons show that the sandwich structure can significantly improve the GMI effect of FINEMET ribbon with a homogeneous structure. Results have demonstrated that the magnetic dipole interaction between the FePd layer and the FINEMET ribbon makes the FePd/FINEMET/FePd composite ribbons obtain a larger GMI effect at low frequencies. The maximum GMI ratio of FePd/FINEMET/FePd composite ribbons reaches 51 %, which is 2.2 times that of bare FINEMET ribbon. The asymmetry degree of GMI curves is up to 85 %. It has the ability to significantly enhance the GMI effect, linearity and reduced the characteristic frequency of composite materials. The experimental results can be explained by the magnetic dipole interaction model. It is a profound significance in the development of a magnetic sensor that can increase the GMI ratio and the linearity.

Magnetic field sensor using the asymmetric giant magnetoimpedance effect created by micromagnets

A magnetic field sensor was developed using the asymmetric giant magnetoimpedance (AGMI) effect. Amorphous ferromagnetic (Fe0.06Co0.94)72.5Si12.5B15 wires were used in this study. The 2-cm-long wire showed an approximately 88% giant magnetoimpedance effect, and the 7-cm-long wire showed an approximately 197% giant magnetoimpedance effect. When two micromagnets were placed 1 cm from the ends of the wire, a distortion in the two peak shapes of the GMI curve was observed, and asymmetry was created by the micromagnets. The 7-cm-long wire showed an approximately 148% AGMI effect. A simple and a new approach was designed to develop a magnetic field sensor. In the design circuit, two signal generators were used to arrange the linearity and dc offset in the output signal. The circuit output showed good linearity and zero hysteresis in the ± 250 A/m and ± 50 A/m magnetic field regions for the 2-cm-long and 7-cm-long wires, respectively.

Exchange coupling and dipolar interactions in FINEMET/Fe50Pd50 composites ribbons

Asymmetrical giant magnetoimpedance (AGMI) effect was investigated in FINEMET/Fe50Pd50 composite ribbons. Composite ribbon samples of 33 μm-thickness FINEMET sputtered with a layer of Fe50Pd50 film were produced, and the microstructure and magnetic properties were investigated. The results showed that the MI response was enhanced by Fe50Pd50 coating layer. The Fe50Pd50 coating layer generates a bias field to FINEMET ribbon, which leads to the asymmetry of GMI curves. The bias field decreases with the increasing of the thickness (t) of Fe50Pd50 coating layer. The asymmetry of GMI curves almost disappears at t = 70 nm. Asymmetry could be tuned by changing the thickness of Fe50Pd50 coating layer, which is analyzed in terms of exchange coupling and dipole–dipole interaction between FINEMET ribbon and Fe50Pd50 layer. The high sensitivity of GMI was used to separate the two interactions for the first time. The results opened the possibilities for application of FINEMET/Fe50Pd50 composite ribbons in linear magnetic field sensors.

A giant magnetoimpedance effect based nonvolatile Boolean logic gate

The biphase magnetic heterostructure (Ni/Fe20Ni45Co25Si2B8/micro-planarcoil/Fe20Ni45Co25Si2B8/micro-planar coil/Fe20Ni45Co25Si2B8/Ni) bonded with a pair of thin magnets shows an improved asymmetric and hysteretic giant magnetoimpedance (GMI) effect with respect to an external dc magnetic field. This is attributed to the modification of the soft amorphous magnetic alloy’s (Fe20Ni45Co25Si2B8) permeability by the hysteretic magnetostrictive stress from the neighboring magnetostrictive Ni layer besides the magnetostatic coupling. More importantly, nonvolatile logic gates, such as NOR and NAND, can be implemented with either a single GMI laminate or arrays. On one hand, after applying two sequential magnetic field pulses as the logic inputs to a single proposed laminate, the nonvolatile output voltages are positive high (logic 1) or positive low (logic 0) depending on the signs and magnitudes of pulses. On the other hand, after applying the magnetic field pulses parallel to the GMI laminates arrays, different logic functions can be programmed and realized at run-time. The integration of memory and logic functions enables the proposed GMI laminate to be a possible candidate for future computing systems beyond von Neumann architecture.

Formation of asymmetric giant magnetoimpedance in amorphous ferromagnetic wires by micro magnets

Asymmetric giant magnetoimpedance (AGMI) was created using two micro magnets placed at 1 cm away from the ends of amorphous ferromagnetic non-magnetostrictive (Fe0.06Co0.94)72.5Si12.5B15 wire. At low frequencies, single-peak behaviour of the AGMI was observed, and the AGMI curves exhibited two-peak behaviour within high-frequency range. The asymmetry in the magnetization curves of amorphous wire with two micro magnets having the same orientation was found, the maximum of the GMI ratio at positive field region decreases from 515% to 356%, and the peak value at negative field region decreases from 513% to 261% at 1 MHz driving current frequency. A linear change in the AGMI curves was obtained, which could be of importance for magnetic sensor applications. Experimental results were qualitatively explained in the framework of a model for the AGMI response in amorphous wire taking into account effects of bias field induced by micro magnets.

Asymmetric giant magnetoimpedance effect created by micro magnets

Asymmetric giant magnetoimpedance (AGMI) effect has been investigated in as-prepared and current annealed amorphous (Co0.9Fe0.05Ni0.05)75Si15B10 ribbons. Asymmetry was created by micro magnets. Different numbers of magnets were used and it was found that increasing number of magnet, the shift in AGMI curves increases. When two micro magnets were placed 1 cm away from the ends of ribbon, a distortion in two peak shape of the GMI curve was observed. At high frequency range, a linear change in the AGMI was observed for the current annealed sample.

Magnetoimpedance effect in FINEMET/Ni80Fe20 composite ribbons

Giant magnetoimpedance (GMI) always attracts much attention owing to its importance in promising applications of industrial devices. Although GMI effect of ribbons have been studied for years, the composite ribbons coated with various films are still attractive due to its high sensitivity with respect to the applied magnetic field. Mostly, the magnetic properties were commonly inspected by hysteresis loops, which may not sensitive enough for Fe-based composite ribbons. Herein, by using both hysteresis loops and the GMI measurement, the magnetic properties of the FINEMT ribbons coated with different thickness of Ni80Fe20 film on free side, wheel side and twin sides have been thoroughly analyzed. It is revealed that the shift of anisotropy direction from preferable transverse to partially longitudinal as the film thickness increased, which affected the interaction between ribbon and Ni80Fe20 coating. Moreover, the asymmetric GMI response could be obtained on the ribbon coated with Ni80Fe20 film on single side, whereas the symmetric GMI response was observed for twin-side coating, which indicated the dipole interaction in the composite ribbons. We found that the ribbon with 260 nm Ni80Fe20 film showed the optimized transverse anisotropy, leading to the smallest Hc and the optimal soft magnetic properties. Hence, GMI measurement can be a sensitive alternative tool to investigate dipole interaction, which can be employed to manufacture novel linear GMI sensors and to properly regulate the operation field.

Cycle rapid cooling treatment effect on the magnetic properties and giant magnetoimpedance properties of Co-based amorphous alloy ribbons

The influence of cycle rapid cooling treatment on the giant magnetoimpedance (GMI) properties in Co-based amorphous alloys was investigated. Hysteresis loops show that the saturation magnetization of ribbons has been improved by cycle treatment. It can be found that the GMI ratio was increased from 89% to 130% at 1MHz by the thermal cycle (TC) treatment. Moreover, GMI ratio of TC treatment sample increased up to 321% at 5MHz. It is considered that internal thermoelastic stress leads to surface roughness, magnetic domain structures and saturation magnetization changes of the ribbons during different cycle processes. It was also found that the asymmetric GMI (AGMI) phenomenon occurred in the Co-based alloys with TC treatment after annealing, which can be regarded as a new method to get GMI-valve to improve GMI sensitivity.

Asymmetric giant magnetoimpedance of Co-rich melt-extraction microwires

The giant magnetoimpedance(GMI) effect of Co-rich microwires makes an opportunity to design sensitive GMI weak magnetic meter sensor. Optimization of magnetic meters needs to improve the GMI response, especially the field sensitivity of microwires. In this study, Co-rich amorphous microwires each with an average diameter of 32 μm are prepared by melt-extracted technique and their GMI characteristics are investigated at frequencies ranging from 0.1 to 10 MHz with and without bias direct voltage applied. Experimental results indicate that the GMI effect of these wires has asymmetric features with the increases of frequency and driving current. It is found that the intrinsic asymmetric GMI (AGMI) response results from the helical anisotropy and magnetization hysteresis of the Co-rich microwires. Furthermore, it is found that there is a pronounced improvement in AGMI response when a bias voltage is applied. In theory, the factor which induces an increase in circular magnetic field causes successive changes in magnetization reversal of the quickly quenched Co-rich microwires with multiple domains and helical anisotropy. As a consequence, the circular magnetization process is enhanced, leading to higher circular permeability and stronger GMI response. Meanwhile, a bias voltage inducing the given circular magnetic field reinforces the magnetization process in a certain direction, which intensifies the asymmetric characteristic of GMI response. For example, the asymmetric ratio between two impedance peaks rises from 1.46% to 12.06% at 1MHz and 3 mA after applying a 1 V bias voltage. Simultaneously, the circular field inclines the magnetization off the axial direction which makes the axially induced magnetization reversal more difficult and occur at a higher switching field. This effect broadens the linear impedance zone; however, it reduces the slope of the impedance with the external field and the field sensitivity increasing to some extent. The balance between these two sides proves that AGMI response is related to the magnetization reversal process which is sensitive to the circular magnetic field. Experimental results indicate that the field sensitivity rises from 616 to 5687 V/T with the impedance linear zone broadening from 0.65 to 1.16 when a 1 V bias voltage is applied, while it decreases to 4525 V/T when the bias voltage futher increases to 2 V at 10 MHz and 5 mA. This reveals that the GMI effect of these amorphous Co-rich microwires with high field sensitivity can be optimized by applying proper bias voltage.

铁基合金的纵向驱动非对称巨磁阻抗效应

研究了直流电流退火的Fe73.5Cu1Nb3Si13.5B9合金薄带的巨磁阻抗效应，实验发现，经0.72 A电流退火10 min后，样品巨磁阻抗比有最大值1810.4%。经0.74 A电流退火10 min后，样品由于自身存在偏置场，其巨磁阻抗效应开始出现零磁场的非对称现象，结合XRD图谱分析表明，样品非对称巨磁阻抗效应的产生与B6-Fe23硬磁相的析出有关。 We have investigated the giant magneto-impedance effect ofFe73.5Cu1Nb3Si13.5B9 alloy ribbons which were annealed by DC current. It was found that the maximum GMI ratio was 1810.43% after 10-min annealing current of 0.72 A. However, the GMI effect began to show asymmetric phenomenon around zero magnetic field after 10-min annealing current of 0.74 A in terms of its own existence bias field. XRD spectrum analysis indicated that the B6-Fe23 hard magnetic phase precipitated should be responsible for the asymmetric giant magneto-impedance effect.

A High Dynamic Range GMI Current Sensor

The design and performances of a high dynamic range DC-AC current sensor utilizing Giant Magneto-Impedance (GMI) are presented. The sensor is based on a GMI element with negative feedback. The sensing element is a 30 μm diameter GMI Co-based amorphous wire. It is curled to a toroidal core of 2 cm diameter. A bias magnetic field of about 650 A/m is applied to the GMI element to obtain an asymmetric GMI effect. A strong negative feedback is introduced to ensure linearity in a wide dynamic range. Analog conditioning electronics was fully developed. This includes a square wave oscillator based on an inverter trigger; a peak detector and a high gain amplifier with zero adjust. The GMI element is driven at a 3 MHz frequency and 5 mA peak-to-peak current. The closed-loop operations are investigated and the performances of the sensor are presented. DC current measurements are performed. The sensor exhibits good sensitivity and very good linearity, free from hysteresis, in a wide dynamic range of ±40 A. The sensitivity is about 0.24 V/A and the linearity error is about 0.02% of the full scale (FS). The hysteresis error is smaller than the measurement accuracy. AC current measurements using the developed sensor have also been successfully achieved. The sensor bandwidth in closed-loop was about 1.7 kHz.

Sensitivity improvement of GMI magnetic and pressure transducers for biomedical measurements

This work presents an experimental study aiming the sensitivity optimization of Giant Magnetoimpedance (GMI) sensors, by means of properly choosing the values of their conditioning parameters. The optimized GMI sensors, together with the development of improved transduction electronic circuits, can lead to the sensitivity enhancement of GMI biomedical, pressure and magnetic transducer prototypes, previously developed by the research group at LaBioMet, PUC-Rio. Those prototypes are, respectively, aimed at the measurement of arterial pulse waves and the localization of magnetic foreign bodies inserted in the human body. Thus, the experimental characterization of GMI ribbon-shaped samples (Co 70 Fe 5 Si 15 B 10 ) was performed, as a function of the external magnetic field, including the experimental evaluation of the asymmetric GMI effect (AGMI). The parameters that affect the behavior of the GMI samples were experimentally analyzed, such as the DC level (0 mA to 100 mA) and frequency (100 kHz to 10 MHz) of the excitation current, as well as the samples length (1 cm, 3 cm, 5 cm and 15 cm). The conditioning parameters, experimentally identified, that optimize the GMI samples sensitivity lead to a maximum specific sensitivity of 0.84 W·Oe -1 ·cm -1 (8400 Ω ·T -1 ·cm -1 ). A new electronic circuit was developed for conditioning and reading of the GMI samples, which directly contributed to the performance enhancement of both transducers. The electronic circuits developed were evaluated supposing the operation of the GMI samples in their most sensitive region. Comparing to previously developed prototypes, the optimum sensitivity achieved for the new configuration of the GMI magnetic transducer increased about 9 times (from 0.12 mV/nT to 1.08 mV/nT), and the sensitivity of the modified pressure transducer increased approximately 7 times (from 1 mV/Pa to 7 mV/Pa).

공기 중에서 자기장 열처리된 CoFeSiB 비정질 리본에서의 자기 바이어스 효과

비대칭 거대 자기임피던스 효과를 보이는 자기장 열처리된 CoFeSiB 비정질 리본에서 자기 바이어스 현상을 MOKE 방법을 이용하여 연구하였다. 열처리 과정에서 리본의 양 표면에 형성된 경자성 결정층이 내부 연자성 비정질 상의 자화특성에 미치는 영향을 조사하기 위해 열처리 후 화학적 에칭에 의해 한쪽 및 양쪽 표면의 결정층을 깎아낸 시편들을 준비하고 각 시편에 대해 비정질 상의 자화곡선을 MOKE 방법으로 측정하였다. 열처리 과정에서 표면에 형성된 경자성층이 내부의 비정질 연자성 상에 바이어스 자기장을 작용하고 있다는 것과 바이어스 자기장의 방향이 경자성층의 자화방향에 반대 방향임을 자기이력곡선의 이동을 통해 확인하였다. Magnetic bias phenomena of field-annealed CoFeSiB amorphous ribbons showing asymmetric giant magnetoimpedance was investigated by MOKE method. The specimens removed the crystalline layer at one surface side by chemical etching were prepared and measured magnetization curves by MOKE to investigate the effect of the crystalline layer on magnetization of inner soft amorphous phase. We observed the shift of hysteresis loop, and concluded that the crystalline layer exerts bias field effect on inner soft amorphous phase and the direction of bias filed is opposite to the magnetization direction of surface crystalline layer.

Magnetic Sensor System Using Asymmetric Giant Magnetoimpedance Head

Recently sensitive micro-magnetic sensors are strongly required in various technologies such as BT and IT. This paper gives the comprehensive analysis of the Asymmetric Giant MagnetoImpedance (AGMI) sensor's performance with negative feedback. Asymmetrical behavior of the GMI is required for linear magnetic field sensors as the sensitivity and linearity for magnetic field are the most important parameters in the practical application of GMI to magnetic sensors, and this has been realized by magnetic field annealing in amorphous ribbon. A novel AGMI sensor was developed and the performance of the sensor was carefully studied with and without applying negative feedback. The sensor uses 10 mm times 1 mm times 20 mum Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">66</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sub> ribbon as a sensing element. On applying the negative feedback the sensor shows excellent linearity free from hysteresis, independent of temperature variations. The sensitivity AGMI sensor was found to be 0.27 V/Oe in dynamic range of -2 ~ 2 Oe.

Influence of current amplitude on the nonlinear asymmetric ac volt–ampere characteristics in amorphous ribbons with GMI effect

Asymmetric giant magnetoimpedance (GMI) effect in amorphous ribbons is very promising due to its possible application in developing the highly sensitive linear magnetic-field sensors. In this paper, the model of the nonlinear asymmetric volt–ampere characteristics in field-biased Co-based amorphous ribbon has been established through the time derivative of the longitudinal magnetization component in the ribbon. Its harmonics are also developed by Fourier analysis. The influence of the current amplitude on the nonlinear asymmetric effect has been studied. It is found that when the current amplitude is 8.54 mA, the sensitivity of the first harmonic voltage on the external field is equal to that of the second harmonic voltage. The results obtained are useful for developing the high-sensitive magnetic-field sensors.

Design of a double core linear magnetometer based on asymmetric magnetoimpedance effect in nanostructured Finemet ribbons

Abstract The techniques used to produce magnetic sensors encompass many aspects of physics and electronics and are going to develop with each passing year. In this paper, we introduce a double core giant magnetoimpedance sensor. The sensing elements are provided by heat treating the FeCuNbSiB (Finemet) ribbons at 560 °C for 1 h to achieve a high magnetic permeability associated with the nanostructured state. Sensor cores are exposed to a dc current bias in order to provide asymmetric giant magnetoimpedance (AGMI) behavior. The sensor detects both direction and amplitude of the magnetic field with a sensibility of 2 mV/Oe.

Influence of Frequency and Bias Current on Asymmetrical GMI Effect in Co71.8Fe4.9Nb0.8Si7.5B15 Amorphous Glass-Covered Wires

The Co71.8Fe4.9Nb0.8Si7.5B15 amorphous glass-covered wires (AGCW) are prepared by the Taylor-Ulitovsky technique. The frequency dependence of asymmetrical giant magneto-impedance (AGMI) effect in amorphous glass-covered wires annealed by 70 mA DC current is here presented. The resistance R and the reactance X have been measured, respectively. The real part R and the imaginary part X of impedance play an important role at high frequency and low frequency, respectively. The influence of DC bias current from Ib = 0 mA to Ib = 5 mA at 30 MHz on the GMI effect in the glass-covered wires annealed by 70 mA DC current is investigated. The asymmetry becomes the largest around Ib=1 mA, and finally decreases for the larger bias current Ib=5 mA. The maximum ΔZ/Z ratio of 310% is observed at 58 MHz under 1 mA bias current.

One-dimensional AGMI sensor with Co66Fe4Si15B15 ribbon as sensing element

A novel asymmetric giant magneto impedance (AGMI) sensor was developed and the performance of the sensor was carefully studied. This one dimensional sensor can be further developed as a two-dimensional compass that can be used for navigational purposes. We used commercial Metglas 2714A ribbon. The sensor uses Co66Fe4Si15B15 ribbon as a sensing element.

A model for exchange-biased asymmetric giant magneto-impedance in amorphous wires

A model describing the exchange-biased asymmetric giant magneto-impedance in Joule-heated amorphous wires is proposed. It is assumed that the Joule heating results in the formation of a surface hard magnetic crystalline layer, and the asymmetric giant magneto-impedance is related to the exchange coupling between the amorphous and crystalline phases. The coupling between the surface layer and the amorphous bulk is described in terms of an effective bias field. The model is based on a simultaneous solution of linearized Maxwell equations and the Landau–Lifshitz equation. The calculated field and frequency dependences of the wire impedance are in qualitative agreement with the results of the experimental study of the asymmetric giant magneto-impedance in Joule-heated Co-based amorphous wires.