Maximum GMI Ratio Research Articles

Magnetic anisotropy of NiFeP/Cu composite wire induced by chemical plating under DC current

NiFeP/Cu composite wires were fabricated by chemical plating under DC current. In this work, DC current was adjusted from 0 to 100 mA and the influence of current on the surface morphology, magnetic properties and GMI effect was investigated. It is found that the DC current has little impact on the composition of the coating. However, with the change of current, the surface morphology, plating rate and magnetic properties of the coating have undergone significant changes which in turn affect the GMI effect. As a result, when the appropriate current is applied, a transverse magnetic structure with an anisotropy angle of approximately 26 degrees can be generated, enabling a maximum GMI ratio of 1964 % and a field sensitivity of 463 %/Oe, which shows potential practical application in the 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.

Effect of Coating and Annealing on Giant Magneto Impedance in Co and Fe-Based Amorphous Wires

Effect of coating with different chemical complexes on giant magneto impedance effect (GMI) was experimentally investigated in Fe and Co-based amorphous wires. The successive ionic layer adsorption and reaction (SILAR) technique was used for coating of the samples at room temperature. The SILAR method mainly based on adsorption and reaction on the ions from the solution and rinsing. Co and Fe-based amorphous wires were coated with CoO, asphaltene and ZnO chemical complexes. The coating thickness was determined to be about 1 μm thick. Maximum GMI ratio for Co and Fe-based samples were measured at 4 MHz and 5 MHz frequency, respectively. Influence of annealing at different temperatures on GMI effect was also experimentally investigated in the same samples. The coated samples were annealed at 300 C, 400 C, 500 C and 600 C temperatures in order to stress relief for 30 minutes. It is observed that the GMI ratio on Co- and Fe-based ZnO coated samples was highest at 500 ºC, while it was maximum on CoO coated Co-based samples at 400 ºC and on CoO coated Fe-based samples at 500 ºC. The highest GMI ratio among the measured samples was detected as 216 on the Fe-based, ZnO coated and annealed sample at 500 ºC at 5 MHz, while the smallest GMI ratio, was found to be as 88 on Co-based as-cast sample at 4 MHz. The measurements show that the GMI ratio is a combined effect of coating, annealing and frequency of ac current in a static magnetic field. Keywords Amorphous magnetic materials, SILAR technique, giant magneto impedance. Special Issue of Educational Sciences DOI: 10.7176/JSTR/6-06-03

Multilevel nonvolatile memory based on the hysteretic giant magnetoimpedance effect of heterogeneous magnetic laminate

This work investigates the asymmetric and hysteretic GMI effect of two-phase heterogeneous magnetic laminate consisting of Ni/Fe30Ni45Co18Si2B5/micro-planar coil/Fe30Ni45Co18Si2B5/Ni for nonvolatile memory application. Since the magnetostrictive Ni ribbon produces the remanent magnetoelastic and magnetostatic fields to the neighboring soft amorphous magnetic alloy (Fe30Ni45Co18Si2B5) when the external dc magnetic field is removed, the proposed laminate manifests multi-level remanent impedances depending on the previously applied magnetic field. And the maximum nonvolatile GMI ratio of 130% is obtained at 400 kHz frequency. Furthermore the laminate can function as multilevel nonvolatile memory, which consumes zero standby power without losing data.

Oil-medium current annealing enhanced giant magneto-impedance properties of Co-based metallic microfibers for magnetic sensor applications

Herein, the effect of oil-medium current annealing on GMI characteristics of rotated-dipping Co-based metallic microfibers was investigated systematically. Based on thermophysical parameters of the metallic microfibers (containing glass transition temperature Tg and initial crystallization temperature Tx1), we constructed a steady-state heat conduction model by ANSYS to simulate the temperature field distribution during its oil-medium current annealing process, and further to determine the annealing current intensity range: 50 mA˜300 mA, according to the crystallization degree of cores of microfibers. The experimental results indicated that, in comparison to as-cast Co-based microfibers, the maximum GMI ratio [ΔZ/Zmax]max and the maximum magnetic field response sensitivity ξmax of oil-medium current annealed microfibers were both significantly improved. Among which, [ΔZ/Zmax]max and ξmax of the microfibers annealed at 225 mA can reach 303.1% and 50.6%/Oe, respectively, at the excitation current frequency f =5 MHz, and the maximum response field Hp increased from 1 Oe to 3 Oe. Meanwhile, the magnetic domain arrangement of oil-medium current annealed microfibers became denser, the width of which got smaller, and the transition regions of domain changed into clearer. This improvement of GMI characteristics is closely related to magnetic domain distribution regulated by high-intensity toroidal magnetic field, which was generated during the medium current annealing process. That is, the atomic magnetic moment tends to be closely and orderly adjusted by the combined action of both the magnetic field energy and thermal activation energy.

A Study on Giant Magnetoimpedance Effect in VITROVAC 6025Z Micro-patterned Ribbons

In this paper, micro-patterned cobalt-based amorphous ribbons with different structures are fabricated by MEMS technology, including bonding, lithography and electroplating. The commercial amorphous ribbons (VITROVAC 6025Z) are purchased from VACUUMSHMELZE ® company. The structures of micro-patterned ribbons are designed for meander shape for different turns (one turn, two turns and three turns). The effect of external magnetic field orientation and turns on GMI ratios were studied in the frequency range of 1–40 MHz. It is found that GMI ratios almost all present negative value, which is related to the material property, namely a large coercive force. Compared with the GMI ratios obtained at transverse external magnetic field, the maximum negative GMI ratio obtained at longitudinal external magnetic field is higher. The value of −69.93% is obtained at a current frequency of 20 MHz and the magnetic field of 150 Oe. With the increase of the number of turns, the maximum positive GMI ratio increases from 0.5 % for the one turn sample to the 2.8% for the sample with three turns. The maximum nagative GMI ratio is obtained by three-turns sample. The GMI character of VITROVAC 6025Z micro-patterned ribbon is significant and the microsensor is expected to be used in biological sensing field.

Influence of microstructure evolution on GMI properties and magnetic domains of melt-extracted Zr-doped amorphous wires with accumulated DC annealing

Herein, we reported the influences of accumulated direct current annealing (ADA) on the GMI properties and microstructures of Zr-doped melt-extracted (Co68.15Fe4.35Si12.25B12.25Zr3) amorphous microwires. There indicated that ADA-ed wires enhanced GMI properties and improved the microstructures remarkably in comparison with as-fabricated wires. The maximum GMI ratio [ΔZ/Z0]max and equivalent magnetic circumferential anisotropy field (EMCAF) of ADA-ed microwires were increased to 256.01% and 4Oe at 20MHz, respectively, which are more than nearly 8 and 2times of 33.62% and 1.6Oe for as-fabricated wires, respectively. Moreover, the maximum magnetic field response sensitivity (ξmax) increased to 372.57%/Oe, which is much higher than the as-fabricated wires of 44.71%/Oe. The remarkable enhancement of GMI performance was considered as the microstructural evolution including structural relaxation, appearance of nano-crystallization, and circumferential arrangement of surface magnetic domains. Nano-crystallization degree and circumferential magnetic domains arrangement were effectively improved by actions of Joule thermal energy and circular magnetic field generated ADA as shown in HRTEM and magnetic force microscope (MFM) analysis. Based on above, both the excellent GMI performances and relatively large ξmax values indicate the ADA is an effective annealing technique for thermal treating the melt-extracted amorphous wires which applied for potentially magnetic sensor in detecting low-intensity magnetic fields.

Tailoring giant magnetoimpedance effect of Co-based microwires for optimum efficiency by self-designed square-wave pulse current annealing

Herein, we systematically studied the effect of a novel square-wave pulse current annealing (SPCA) on the magnetic properties and microstructure of Co-based melt-extracted amorphous wires, and efficiently tailored the related experimental parameters by using numerical calculation of transient temperature rise during SPCA process. We obtained the optimal SPCA treatment (at 50Hz, with amplitude of 90mA for 480s) can remarkably enhance the GMI property of as-prepared wires. At 10MHz, the maximum GMI ratio [ΔZ/Z0]max and maxima response sensitivity ξmax of SPCA-treated wire increases to 202.60% and 305.74%/Oe, which is nearly two times and 1.5 times of 104.80% and 208.14%/Oe for as-cast wire, respectively. Especially, at 5MHz, [ΔZ/Z0]max of SPCA-treated wire increases to 185.81%, which is 2.5 times of 73.69% for as-cast wire, and ξmax of SPCA-treated wire increases to 346.65%/Oe by less than two times of 190.16%/Oe for as-cast wire. From mictrostructural perspective, the notably observed role of atomic order orientation regimes and circular magnetic domain during stress releasing or structural relaxation by the co-action of high-density pulse magnetic field energy and thermal activation energy determines the optimum efficiency of SPCA, further to enhance circumferential permeability. In conclusion, SPCA treatment is expected to effectively improve GMI property of microwires, which can be used as sensitive materials for potential sensor application in detecting weak magnetic field.

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.

Giant Magnetoimpedance (GMI) Effect and Field Sensitivity of Ferrofluid Coated Co66Fe2Si13B15Cr4 Soft Magnetic Amorphous Microwire

Co66Fe2Si13B15Cr4 based amorphous microwire was developed at the laboratory using in-water quenching apparatus. The field sensitivity of the wire was enhanced when coated with ferrofluids. The presence of coating also decreased the frequency of the magnetising field 5MHz to 1MHz at which the maximum GMI ratio observed.

Comparative Study on Magnetic Properties and Microstructure of As-prepared and Alternating Current Joule Annealed Wires

Abstract X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), magnetic measurement including impedance measurement were used for investigating the microstructure and magnetic properties of as-prepared and alternating current Joule annealed (ACJA) Co-rich amorphous microwires for potential sensor applications. Experimental results indicated that as-cast and ACJA wires both were amorphous characteristic, while ACJA wire has an enhanced local ordering degree of atom arrangement. There was a transform of magnetic properties after ACJA treatment, namely increasing coercivity, maximum magnetic permeability and saturation magnetization, resulting from the coactions of magnetic anisotropy and magnetic moment exchange coupling. Moreover, ACJA treatment can drastically improve the GMI property of melt-extracted wires. At 5 MHz, the maximum GMI ratio [Δ Z / Z 0]max of ACJA wire increases to 205.93%, which is nearly 4.1 times of 50.62% for as-cast wire, and the field response sensitivity ξ max of ACJA wire increases to 463.70%/Oe by more than 2 times of 212.15%/Oe for as-cast wire. From sensor application perspective, the sensor applied frequency range (SAFR) of ACJA wire is 3MHz-7 MHz (the better working frequency is at 5 MHz). It can therefore be concluded that the ACJA wire (60 mA, 480s, 50 Hz) has better GMI and magnetic properties, is more suitable for potential magnetic sensor applications working at low-frequency and relatively high-working-magnetic field.

Enhancing GMI properties of melt-extracted Co-based amorphous wires by twin-zone Joule annealing

The influence of twin-zone Joule annealing (TJA) on the microstructure and magnetic properties of melt-extracted Co68.2Fe4.3B15Si12.5 amorphous microwires has been investigated. Experimental results indicated that twin-zone Joule annealing treatment improved the GMI property of as-cast wires to a greater extent comparing with Joule annealing (JA) and conventional vacuum annealing (CVA) techniques. At 15MHz, e.g., the maximum GMI ratio [ΔZ/Z0]max of a TJA wire increases to 104.29%, which is more than 5 times of 20.49% for the as-cast wire, nearly two times of 56.47% for the JA wire, while the CVA wire has a decreased GMI ratio; the field response sensitivity of the TJA wire increased to 171.62%/Oe from 80.32%/Oe for the as-cast wire, exceeding the values of 140.76%/Oe for the JA wire and of 39.17%/Oe for the CVA wire. The stress or structural relaxation in TJA wire increases circumferential permeability, and magnetic moment achieves a critical state of excitation for overcoming eddy-current damping or “nail-sticked” action in rotational magnetization process at relatively high frequency. From the microstructural point of view, the role of regularly arranged atomic micro-regions (RAAM) and of medium range order region (MROR) determines the efficiency of various annealing techniques. Conclusively, TJA is established as an efficient annealing technique to enhance the GMI effect of wires, which can subsequently be used for detecting weak magnetic field at relatively wider working range (±2.0Oe).

Effects of Electrolytic Current Density on Structural, Magnetic Properties and GMI Behavior in Electrodeposited Bilayer FeNi/Cu Composite Wires

In this article, a systematic study has been performed on structural, magnetic properties and the GMI effect in electrodeposited FeNi/Cu composite wires in the range of current density from j=15.9 mA/cm2 to 79.5 mA/cm2. Our obtained results reveal a correlation between the structure, magnetic softness, and GMI behavior in prepared wires. Among the samples investigated, the softest magnetic property (lowest coercivity) was found for the wire-sample plated at j=47.7 mA/cm2, which arises from the smallest nanograin size. This results in the largest values of GMI ratio and its sensitivity of this sample, which is ascribed to the optimized domain structure with a well-defined circular anisotropy. It is worthy to note that the maximum GMI ratio and the field sensitivity reached the highest values of 90 % and 7 %/Oe for at a measuring frequency of 5 MHz. This result is very promising for developing high-performance GMI-based sensors applications. Our finding demonstrates that the changes in the surface morphology and the microstructure of prepared wires has led to modification of the surface magnetic properties, and hence GMI effect.

Multiangle combined magnetic‐field annealing of Co‐based amorphous microwires for sensor applications

AbstractThe effect of multiangle combined magnetic‐field annealing (MCMFA) on the GMI performance of melt‐extracted Co‐based amorphous microwires for sensor applications is studied using a precision impedance analyzer. Experimental results indicated that MCMFA treatment can effectively improve the GMI effect comparing with as‐cast and conventional vacuum‐annealed (CVA) wires. The maximum GMI ratio [ΔZ/Zmax]max and field response sensitivity ξmax of transverse combined magnetic‐field annealed (TCMFA, α = 90°) wires can be increased at 10 MHz to 310.7 and 30.91%/Oe, respectively, through with circumferential anisotropy field expanded and GMI changed from single peak (SP) to double peaks (DPs). DPs behavior of TCMFA wire is due to the typically “nail‐sticked” action of magnetic moment rotation at relatively high frequency (up to ≥1 MHz). It can therefore be concluded that MCMFA could be used to develop Co‐based microwires with enhanced GMI effect for high‐resolution sensor applications.

Magneto-Impedance behavior of Co-Fe-Nb-Si-B-based ribbons

The giant magneto-impedance of melt spun CoxFe72−xNb4Si4B20(x=10, 20, 36, 50) amorphous and nanostructured ribbons have been investigated. Alloys have been optimized at the driving current amplitude, frequency and found that amorphous ribbon of nominal composition of Co36Fe36Nb4Si4B20 shown maximum GMI ratio of 13%. The behaviour of the driving current amplitude on the GMI behaviour was studied and the sample was optimized for driving current amplitude, Iac=10 mA. The frequency dependence of the GMI behaviour was studied for the ribbon sample Co36Fe36Nb4Si4B20 at frequency in the range of 100 kHz–1.2 MHz of the optimized driving current amplitude and it was found that the sample showed the maximum GMI behaviour at f=700 kHz. The optimized samples were Joule heated at the current density J=0–35 A/m2 for a period of 1 min. The GMI ratio initially increased then progressively deteriorated with J, but after a certain range it shows up to 16% of improvement in the magneto-impedance value due the increase of nanocrystalline volume fraction. The asymmetry in the GMI profile was observed for the sample Joule heated at J=1–5 A/m2 for 1 min.

Effect of Fe addition on the magnetic and giant magneto-impedance behaviour of CoCrSiB rapidly solidified alloys

Thermal electrical resistivity, magnetic hysteresis and magneto-impedance behaviour of melt spun and annealed Co71−XFeXCr7Si8B14 (X = 0, 2, 3.2, 4, 6, 8 and 12 at.%) were investigated. The addition of Fe in the system changed crystallization as well as the magnetic properties of the materials. The alloy containing 6 at.% Fe showed an increase in resistivity during the first crystallization process. A TEM micrograph indicated the formation of nanostructure during the crystallization process. The GMI properties of the alloys are evaluated at a driving current amplitude of 5 mA and a frequency of 4 MHz. The two-peak behaviour in the GMI profile was observed for all the samples. It is found that the alloy with 4 at.% Fe has the maximum GMI ratio because of the nearly zero magnetostriction value of the sample. About 62% change in the GMI ratio was observed in the alloy with 4 at.% Fe when annealed at 673 K. The anisotropy field was also minimum for the annealed alloy. The results were explained by the formation of directional ordering and the reduction of the magnetostriction constant of the alloy due to nanocrystallization during the annealing process.

The effect of magnetoelastic interaction on the GMI behaviour of Fe-, Co- and Co–Fe-based amorphous wires

The giant magnetoimpedance is the sensitive change in ac impedance value with the application of dc magnetic field when ac current passes through the sample. In the present work GMI properties of positive (Fe 77.5Si 7.5B 15), negative (Co 72.5Si 12.5B 15) and nearly zero ((Co 94Fe 6) 72.5Si 12.5B 15) magnetostrictive amorphous wires have been studied. The result indicates that the magnetostriction constant plays an important role in GMI property. The maximum GMI ratio (330%) and maximum field sensitivity (7% per A/m) are observed in (Co 94Fe 6) 72.5Si 12.5B 15 amorphous wire. The frequency response of the GMI characteristics of the above alloys has been measured and zero magnetostrictive (Co 94Fe 6) 72.5Si 12.5B 15 material showed better frequency response.

Magnetic and magnetotransport properties of Fe-based glass-covered microwires

Magnetic and magnetotransport properties of glass-covered amorphous microwires of nominal composition Fe89B1Si3C3Mn4 have been studied. Samples of two families with the same composition but different metallic core diameters were annealed in a furnace or by Joule heating. The electrical resistance was measured as a function of time during annealing to study the effects on the samples' microstructures (evolution from the amorphous to the crystalline phase). Static hysteresis loops were measured on all samples by means of a vibrating sample magnetometer. Giant magneto-impedance measurements (GMI) performed on a coaxial line using a vectorial network analyser at frequencies up to 6 GHz showed that furnace-annealed samples display larger anisotropies with respect to Joule-heated ones; however, Joule heating is more effective in improving the magneto-impedance response of the alloy. The maximum GMI ratio is ≈ 175% at 4 GHz. The influence of the different metallic core/total wire diameter on the induced anisotropies has been studied for the two families of samples through hysteresis loops and high-frequency GMI.

Tailoring GMI effect in Co-rich glass coated microwires by Joule heating

The dependence of magnetoimpedance ratio, ΔZ/Z = {[Z(H)-Z(Hmax)]/Z(Hmax)}.100%, on the axial magnetic field of soft magnetic Co67Fe3.85Ni1.45B11.5Si14.5Mo1.7glass coated amorphous microwires has been investigated in the frequency range 1 - 30 MHz, for the driving current amplitudes 0.75 - 5 mA, and at the maximum axial DC-field of 8 kA/m. In the as-prepared sample, maximum GMI ratio, ΔZ/Zmax≈380%, has been observed at the highest used frequency (30 MHz). It has, however, been shown, that Joule heating enables to enlarge the ΔZ/Zmax ratio up to 500%. A strong dependence of ΔZ/Zmax on annealing time, frequency and amplitude of the driving current has also been observed. The results of the GMI measurements, presented as a function of the annealing time with the frequency and current amplitude as the parameters, showed an increase of the anisotropy field with an increase of the annealing time and temperature. The observed dependencies have been interpreted in terms of stress relaxation and changes of the magneto-elastic anisotropy induced by the Joule heating.

Magnetoelastic sensor based on GMI of amorphous microwire

The magnetoelastic sensor based on the stress dependence of the GMI effect in Co 68.5Mn 6.5Si 10B 15 amorphous microwire has been introduced. This amorphous microwire after adequate heat treatment shows the maximum GMI ratio (Δ Z/ Z) m up to around 130%. GMI effect of this microwire has been found to be affected by the magnetoelastic anisotropy induced in the sample by the applied tensile stress. This stress dependence of the GMI induces changes on the ac voltage measured between the ends of the sample placed in the magnetic field under applied tensile stress. When the sample is under a load of 3 g such change of the ac voltage across the microwire is about 3.5 V.