Asymmetric magnetoimpedance effect and dipolar interactions of FINEMET/SiO_(2)/FePd composite ribbons

The dipolar interactions are investigated through the asymmetric magneto-impedance in FINEMET/SiO_(2)/FePd composite ribbons.The interface between the hard(FePd layer)phase and soft(FINEMET ribbon)phase is coherent by SiO_(2)layer in FINEMET/SiO_(2)/FePd composite ribbons,which effectively induces dipolar interactions.The contribution of dipolar interaction to the bias field(Hb)by asymmetrical giant magneto-impedance and magnetic properties is analyzed.The results show that Hb response decreases with the increase of the SiO_(2)layer thickness,indicating that the linear region near-zero field can be tuned by the thickness of SiO_(2)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.

Giant magnetoimpedance effect in Fe-Zr-Nb-Cu-B nanocrystalline ribbons

The giant magnetoimpedance effect of the nanocrystalline ribbonFe_(84)Zr_(2.08)Nb_(1.92)Cu_1B_(11) (atom fraction in %) was investigated. There is an optimumannealing temperature (T_A≈ 998 K) for obtaining the largest GMI (giant magneto-impedance) effectin the ribbon Fe_(84)Zr_(2.08)Nb_(1.92)Cu_1B_(11). The ribbon with longer ribbon length has strongerGMI effect, which may be connected with the demagnetization effect of samples. The frequencyf_(max), where the maximum magnetoimpedance GMI(Z)_(max) = [(Z(H) - Z(0))/Z(0)]_(max) occurs, isnear the intersecting frequency f_i of the curves of GMI(R), GMI(X), and GMI(Z) versus frequency.The magnetoreactance GMI(X) decreases monotonically with increasing frequency, which may be due tothe decrease of permeability. In contrast, with the AC (alternating current) frequency increasing,the inagnetore-sistance GMI(R) increases at first, undergoes a peak, and under then drops. Theincrease of the magnetoresistance may result from the enhancement of the skin effect with frequency.The maximum magnetoimpedance value GMI(Z)_(max) under H = 7.2 kA/m is about -56.18% at f= 0.3 MHzfor the nanocrystalline ribbon Fe_(84)Zr_(2.08)Nb_(1.92)Cu_1B_(11) with the annealing temperatureT_A= 998 K and the ribbon length L = 6 cm.

Giant Magnetoimpedance Effect of As-Spun Nanocrystalline Ribbon of FeZrBCu Alloy

The melt-spun nanocrystalline ribbons of Fe86.5Zr7B4Cu2.5 alloy were prepared by single wheel technique with wheel surface velocity of 37 m/s.It is found that there appears a lot ofα-Fe nanoparticles with sizes of 5-10 nm in as-spun nanocystalline ribbons which exhibit giant magnetoimpedance(GMI)effect.The GMI ratio up to 33.69% at frequency f=1MHz under a DC field of 5 172A/m can be obtained.

Giant magnetoimpedance effect in as quenched Fe_(89-x)Zr_7B_4Cu_x(x=1.0-2.5) ribbons

The giant magnetoimpedance(GMI)effect in as-quenchedFe_89-xZr_7B_4Cu_x(x=1.0-2.5)ribbons is reported. The as-quenchedFe_89-xZr_7B_4Cu_x(x=1.0-2.5)ribbons were prepared by the vacuummelt-spun processes with the quenching speed of 37 m/s. The magne-Toimpedance measurement were performance at room temperature, wherethe current flow through the length of the ribbons in the directionParallel to the dc fields. results show that values Z(impedance),R(resistance)for both H = 0 A/m and H = 5 127 A/m Increases withincreasing ac frequency. This can be explained by the skin effectmechanism.

Giant Magnetoimpedance of Cube/Feconi Electroplated Wires: Focus on Angular Sensoric

Giant magnetoimpedance effect (GMI) is a subject of special interest proved by applied electrodynamic and technological applications. GMI effect in ferromagnetic tubes is connected with the high sensitivity of the magnetic system to a circular magnetic field near the spin-reorientation magnetic phase transitions offering high sensitivity with respect to an external magnetic field. In this work the non-magnetic CuBe wires were covered by Fe20Co6Ni74 layers by electrodeposition. The thickness of 1 μm for magnetic layer was high enough in order to ensure the high GMI value. Longitudinal magnetic anisotropy was induced by post preparation annealing in a magnetic field of 160 A/m at 320℃ during 1 hour in order to obtain appropriate magnetisation process. Angular dependencies of GMI were measured in a frequency range of 1 to 10 MHz for driving currents of 2.5 to 20 mA. High longitudinal GMI of the order of 400% was observed at quite low frequency of 1 MHz. The highest value of the sensitivity of 520%/Oe was found for the active resistance: Linear sensitivities of 0.023 Ω/° and 0.05 Ω/° were observed for reasonably low fields of 240 and275 A/m respectively for small angles, where planar GMI elements are less effective.

Giant magnetoimpedance effect of multilayered structure(F/SiO_2)_3/Ag/(SiO_2/F)_3 films deposited in a longitudinal magnetic field

The soft magnetic properties and giant magnetoimpedance(GMI) effect of the multilayered structure(F/SiO2)3/Ag/(SiO2/F)3(F≡Fe71.5Cu1Cr2.5V4Si12B9) films,which were prepared by radio frequency sputtering without and with a longitudinal magnetic field of about 72 kA/m,are studied.The results show that the GMI effect almost cannot be detected in the samples deposited without field,whereas,a longitudinal magnetic field applied during deposition process obviously optimizes the soft magnetic properties of the films,and noticeable GMI effect is obtained.The maximum values of the longitudinal and transverse GMI ratios are 45% and 44% at the frequency of 6.81 MHz,respectively.In addition,the dependence of magnetoimpedance ratio,magnetoresistance ratio,magnetoreactance ratio and effective permeability ratio on the frequency has been investigated.We found that the GMI spectrum curves in the longitudinal and transverse cases almost overlap for the field-deposited sample.The GMI effect is mainly a giant magnetoinductive effect at low frequencies.When f >9 MHz,magnetoreactance ratio changes to a negative,i.e.,the property of reactance changes from inductive to capacitive.

Magnetoimpedance of Electroplated Wires with Large Core Diameters

Monolayered Co and trilayered Co/Cu/Co were electroplated on 485 μm-diameter Cu wires using the bath pH 2.5. These wires can be functioned as magnetic sensors owing to their magnetoimpedance （MI） effect. By measuring at four different frequencies （100, 250, 500, and 1000 kHz） and Co thicknesses （2.5, 5.0, 10.0, and 25.0μm）, the MI ratio of electroplated Co on Cu wires tended to increase with increasing Co thickness and frequency of the driving current. The Co/Cu/Co on Cu wires exhibited even higher MI ratio. The magnetic layer also regulated the magnetic inductions and anisotropy regardless of the size of nonmagnetic core. Nevertheless, the diameter of the Cu core had a significant effect on the MI ratio. By comparing with the 47.7 μm-diameter Ag cores electroplated by Co and Co/Cu/Co of the same thickness, the Cu cores with a larger diameter gave rise to a larger MI ratio because their lower electrical resistance enhanced the crossing effect. Substantial MI ratio was observed even in a low frequency regime because the skin effect occurred at a low frequency in the case of electroplated wires with large core diameters.

Influence of Aspect Ratio on Giant Magnetoimpedance Effect for Fe_(67)Co_(18)Si_(11)B_4 Amorphous Ribbons

The effect of sample geometry aspect ratio （l/w） on the giant magnetoimpedance （GMI） in Fe67Co18Si11B4 amorphous ribbons was investigated systematically. The GMI profiles were measured as a function of the external magnetic field at different frequencies up to 110 MHz. The results show that there exists a critical aspect ratio （（l/w）0 = 5.4） below which the maximum GMI effect and sensitivity η decrease with decreasing l/w and above which the maximum GMI effect keeps almost constant and η decreases with increasing l/w. The observed dependence on aspect ratio as （l/w） 〈 （l/w）0 is correlated with the magnetization process： Complex domain structures emerged near the ribbon ends to decrease the magnetostatic energy, modify the transverse permeability and consequently GMI response. Contributions from transverse permeability and resistance may dominantly determine the change of GMI effect as （l/w） 〉 （l/w）0.

Giant Magneto-impedance Effect in Composite Wires with Different Core Layer

Composite structure materials were potential sensing elements for magnetic sensors due to Giant magnetoimpedance(GMI) effect. Two kinds of composite wires with different magnetic/non-magnetic structures were fabricated by using electroless deposition methods and the magnetoimpedance properties were investigated. The maximum GMI ratio of 114% was acquired at 60 MHz in the composite wires with a ferromagnetic core, whereas, 116% of maximum GMI ratio was found in the composite wires with a conductive core at low frequency of 600 k Hz. These results exhibit that the GMI ratio reaches the maximum when magnetoresistance ratio ?R/R and magnetoinductance ratio ?X/X make the comparative contributions to the total magnetoimpedance(MI). The obvious GMI effect obtained in the composite wires with conductive core frequency may provide a candidate for applications in magnetic sensors, especially at low frequencies.

Giant Magneto-Impedance of Co50Ni22Ga28 Alloy with High Chemical Ordering

The microstructure of CosoNi22Ga28 ribbon with the L10 structure is examined. The band-like morphology is observed. These bands with the width in a range of 40-200 nm appear along the transverse direction of the ribbon. The giant magnetoimpedance （GMI） effect in this alloy is measured. The results show that Co5oNi22Ga28 exhibits a sharp peak of the GAI effect. The maximum GAH ratio up to 360% is detected. The GMI effect measured versus temperature shows large jumps of the magnetoimpedance amplitude at the reversal martensitic transformation temperature 240℃ and Curie temperature 375℃C respectively. The jump ratios of the magnetoimpedance amplitude examined at these temperatures are about 5 and 10, respectively.

Enhancement of GMI Effect in Silicon Steels by Furnace Annealing

The ratio and sensitivity of giant magnetoimpedance （GMI） in grain oriented silicon steels （Fe-4.5%Si） are improved after furnace annealing in air for 20 min. By annealing at 800℃, the GMI sensitivity rises from 1.29%/Oe to 1.91%/Oe and the ratio increases from 237% to 294% with decreasing characteristic frequency. The results are attributable to an increase in the transverse magnetic permeability during the heat treatment. From simulation by finite element method, the GMI effect can be interpreted as the modification of the current distribution by the applied magnetic field via the transverse permeability. In the case of annealed samples,the larger transverse permeability allows a higher GMI ratio and sensitivity.

Low field microwave absorption and magnetization process in CoFeNi electroplated wires

Ferromagnetic resonance （FMR）, Ferromagnetic antirresonance （FMAR） and low field magnetoimpedance （MI） are the characteristic features of high frequency losses in applied fields. While some results on FMR and FMAR in CoFeNi electroplated wires were reported earlier, here we present microwave absorption in CuBe wires electroplated by 1 μm FeCoNi magnetic layer at very low fields. These data are comparatively analysed together with longitudinal hysteresis loops in order to reveal the correlation between power absorption and magnetization processes. Microwave studies are made by using the cavity perturbation method at 9.65 GHz for a DC field parallel to the sample axis, and with microwave magnetic field hrf parallel or perpendicular to the wire axis. Two peaks have been observed in all samples, one is due to FMR, and the other is, at very low fields, related to MI. The MI peaks represent minima in power absorption. By comparing with the hysteresis loop we remark the close correspondence between the MI phenomena in the axial mode and the concomitant magnetization process.