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 effect in stress-joule-heated Co-based amorphous ribbons

Co-based Co63Fe4B22.4Si5.6Nb5 amorphous ribbons with a width of 150 μm and a thickness of 50 μm were prepared by single-roller melt-spinning process.The giant magneto-impedance(GMI) effect of the stress-joule-heated ribbons under applied tensile stress ranging from 37 to 148 MPa was investigated.Experimental results show that the spectra of GMI ratio vs.external direct current(dc) field(Hex) of the samples changes dramatically with annealing tension() and driving frequency.The single-peak(SP) GMI curve with maximum GMI ratio of 260% and magnetic field sensitivity of 52%/Oe was obtained in the sample applied tensile stress of 74 MPa at frequency of 3.6 MHz.A three-peak behaviour appeared in the samples under σ of 111 and 148 MPa.The uncommon three-peak behaviour was attributed to several factors,which effectively originated from the balance between domain-wall movement and magnetization rotation.

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 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.

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.