Fe-rich Amorphous Wires Research Articles

Influence of Organic Coating on the Giant Magneto Impedance Characteristics of Fe-Rich Amorphous Wire

Influence of organic coating on the giant mag- neto impedance effect was experimentally investigated in Zn complex-coated dielectric Fe-based amorphous wires and optimized the giant magneto impedance (GMI) effect using artificial neural networks and MATLAB. A three- node input layer, a one-node output layer and three hidden layers with 21 neurons and full connectivity between nodes were developed with the transfer functions hyperbolic tan- gent in hidden layers and sigmoid in output layer. The input parameters were frequency, static magnetic field and sample type, while the output parameter was the giant mag- neto impedance effect. When the network performance was tested using untrained sample data, the average correla- tion and prediction error of giant magneto impedance effect were found to be 99 and 0.4 %. An analytical equation as depending on experimental data has been determined by using MATLAB Curve Fitting Toolbox™for giant mag- neto impedance. The square of the correlation and the root meansquared error were found to be 99 % and 0.89 respec- tively. The models including the different kinds of samples prepared have a good prediction capability and agreement with experimental results.

Influence of the Circular Magnetic Field and the External Stress on the Remagnetization Process in Fe-Rich Amorphous Wires

The remagnetization process of Fe-rich wires as dependent on the circular magnetic field induced by the AC current flowing through the wire is investigated experimentally. We present the dependence of the switching field on the amplitude and frequency of the circular magnetic field and its variance with the applied tensile stress. The results are interpreted in terms of magnetic domain structure of the wire.

Study of microwave magnetoimpedance effect in amorphous FeSiB wires

Measurements of microwave magnetoimpedance of melt-extracted Fe-rich amorphous wires are presented. These wires were simultaneously submitted to a microwave electromagnetic wave propagating at the wire surface, Joule heating and circumferential static magnetic field. This field is generated by a DC electric current flowing through the wire with maximum strength of 90 mA in order not to reach the recrystallization temperature of the amorphous alloy. The impedance was measured up to 6 GHz using a technique based on the s-parameters measurement of a custom-designed coaxial line by means of a vectorial network analyzer. The real part of the impedance spectra we obtained show peaks, which characterize the magnetic losses occurring in the amorphous material. These peaks shift toward lower frequency for stronger DC currents. Theoretically, these results can be accounted for by the fact that the peaks frequency represents the ferromagnetic resonance occurring in the magnetic material. Its magnitude depends on the saturation magnetization. Since this magnetization decreases with temperature following the Curie law, the resonance frequency also decreases and the impedance peaks shift towards lower frequency.

Studies of the remagnetization process in cold drawn Fe-rich thin amorphous wires

Results on local hysteresis loops for Fe-rich amorphous cold-drawn wires with the sample lengths of 30 mm and 70 mm under applied stress, σ, up to 1300 MPa are reported. For both lengths, the magnetization, M, increases with σ and the coercive field, H C, decreases. Near the wire end, M results to be larger than at the wire center, and H C sharply decreases. This reduction is eliminated if the applied stress is large enough. It is assumed, that the magnetic configuration at the wire end for the cold-drawn wires is different from the other wires families.

Distribution of switching field fluctuations in Fe-rich wires under tensile stress

We present experimental results on the influence of the applied tensile stress on switching-field distribution in as-cast Fe-rich amorphous wires. The fluctuation spectrum of the switching field reveals two different mechanisms, namely (i) magnetoelastic coupling of the domain wall with internal stresses, which significantly varies with the applied stress, and (ii) pinning of the domain wall at defects of the atomic scale.

Helical magnetic structure in cold-drawn Fe-rich amorphous wire

The magnetic and microstructural study of Fe-rich cold-drawn amorphous wire has been performed. The influence of the current annealing on the process of the formation of helical magnetic structure in the surface area of the wire has been investigated. The correlation between the magnetic and structural properties of cold-drawn wire is discussed.

Two magnetic phases in cold-drawn Fe-rich amorphous wire

Magnetic properties have been studied in ferromagnetic amorphous wires of nominal composition Fe 77.5B 15Si 7.5 and diameter 0.05 mm prepared by cold-drawing technique. Conventional and surface hysteresis loops were measured by fluxmetric method and by magneto-optical Kerr effect method, respectively. Saturation magnetization dependence with the current density has been obtained. Two Curie points were clearly distinguishable on this dependence that could be associated with the existence of two ferromagnetic phases. On the other hand, two successive jumps of magnetization have been observed in fluxmetric as well as in magneto-optical curves. The joint analysis of the bulk and surface hysteresis loops permits us to conclude that the cold-drawing post process induces strong helical anisotropy in the Fe-rich wires studied. The helical magnetic structure exists in the surface and, also, in the volume of the wire. We consider that the helical magnetic structure forms the separate magnetic phase that finds the reflection in the two Curie points behavior.

Asymmetrical magneto-impedance effect in Fe-rich amorphous wires

Magnetoimpedance and magnetic properties of Fe-rich ferromagnetic amorphous wires of 0.050 mm diameter, prepared by an in-rotating-water technique following by a cold-drawing process to reduce the initial diameter of 0.125 mm, have been studied. A high value of magnetoimpedance phenomenon (about 60% real component and about 300% imaginary component) was measured in these microwires submitted to stress annealing by using the current annealing technique (annealing parameters: 150 mA during 90 min and 200 MPa). The application of a dc bias current affects strongly the field dependence of the magnetoimpedance ratio, inducing asymmetrical shape to the magnetoimpedance ratio. Such asymmetrical character is associated with the intrinsic helical anisotropy. The dc circular magnetic field produced by the dc electric current can modify in different ways the surface domain structure.

Investigation of magnetic structure in cold-drawn Fe-rich amorphous wire

Magnetic properties of Fe-rich amorphous wires, prepared by in-rotating-water-quenching technique and submitted to a post cold-drawing process (to reduce the initial diameter) have been studied. The experiments have been performed using magneto-optical Kerr effect and fluxmetric methods in crossed axial and circular magnetic fields. The helical magnetic structure has been found in the surface and in the volume of the wire. The angle of helical anisotropy has been evaluated to be around 45° with respect to the axial direction at the surface of the wire decreasing to 39° through the volume of the wire.

Correlation among impedance, longitudinal and circumferential permeability in Fe-based amorphous wires

A correlation is made among the impedance, the longitudinal permeability and the so called circumferential permeability in Fe-rich amorphous wires. The measurements of longitudinal permeability are made while an AC driving current is flowing through the wire for measuring the impedance components L and R . For particular combinations of the amplitude of the AC driving current, its frequency and the axial test field frequency, the longitudinal relative permeability achieves very high values (40–50×10 3) in comparison with those (1–2×10 3) measured in absence of the AC driving current. The circumferential permeability, deduced from the values of L and R, increases too but the increases are moderate in comparison with those of the longitudinal permeability and are favoured by torsional stresses. The results, discussed on the basis of the domain core-shell model, are ascribed to a coupling between the magnetization variations occurring in the outer shell of the wire and those occurring in the inner core due to the concomitant effect of the AC circular field and the AC axial field.

Torsional impedance effect in Fe-rich amorphous wires

An amorphous ferromagnetic wire with a highly positive saturation magnetostriction constant, made of Fe 73.5Si 13.5B 9Nb 3Cu 1, was simultaneously submitted to both, an AC current flowing through it and a torsional stress, in order to induce a helical magnetic anisotropy that modifies the magnetic domain structure and therefore the magnetic response of the sample. We study the torsion-impedance effect in an Fe-rich amorphous wire when it is submitted to different applied torsional stresses in both senses, up to 0.8 π rad/cm, as a function of the drive current frequency, in the range of 10 Hz–2 MHz. The experimental results are explained on the basis of the core-shell magnetic structure model combined with the skin effect.

Torsional stress dependence of reactance and resistance in Fe-rich amorphous wires at low frequencies

Amorphous ferromagnetic wire with a highly positive saturation magnetostriction coefficient, made of Fe 73.5Si 13.5B 9Nb 3Cu 1, was simultaneously submitted to both, an AC current passing through it and a torsional stress, in order to induce a helical magnetic anisotropy in the wire that modifies its domain structure and therefore the magnetic response of the sample. The aim of this work is to study the reactive, resistive and impedance behaviour in this Fe-rich wire, submitted to different applied torsional stresses, and for several values of the AC current amplitude through the wire (5–20 mA rms), in the low frequency range, f<MHz. The experimental results are explained on the basis of the core-shell model.

Length effect in a negative magnetostrictive Co–Si–B amorphous wire with rectangular hysteresis loop

Magnetization and coercivity profiles of Co-rich amorphous wires with negative magnetostriction have been measured for the sample lengths of 3–12 cm. Observed dependencies suggest that the critical length for Co-rich wires is around 4 cm, being much less than in Fe-rich amorphous wires. Estimations of domain wall velocity and inner axially magnetized core diameter have been made.

Axial-field-dependent circular susceptibility in Fe-rich amorphous wires

The longitudinal magnetic field dependence of low-frequency circular susceptibility, χ( H), is measured for (Fe 1− x Cr x ) 77.5Si 7.5B 15 ( x=0,0.05,0.1, and 0.15) amorphous wires of radius r 0=0.07 mm. In order to explain the experimental results, on the basis of the widely accepted core–shell model, we consider that there are a constant axial anisotropy K c in the core and a radius-dependent radial anisotropy K s∝ r 8/ r 0 8 in the shell, both K c and K s being functions of stress-energy constant λ s σ 0. A formula for χ( H) is derived from this model. The experimental data fits indicate that the magnetic structure can be well described by the improved core–shell model with reasonable values of λ s.

Bending effects and temperature dependence of magnetic properties in a Fe-rich amorphous wire

Amorphous wires with composition Fe 77.5Si 7.5B 15 exhibit a very peculiar magnetization process characterized by a single and quite large Barkhausen jump. This gives rise to a squared hysteresis loop at a critical magnetic field. The bistable behaviour, widely studied in wires with typical length of 10 cm and diameter of 125 μm, appears above a length of about 7 cm in straight wires and disappears for curvature radius within the range 2–12 cm in bent wires. In this work it is shown that bistability occurs in bent wires, whatever their curvature is, provided the wires are long enough. To this purpose spiral-shaped samples with several turns are considered. However, when the wire length is not a integer number of turns the magnetization reverses through many large Barkhausen jumps. In this condition, varying the measuring temperature can activate the energy barriers for the jumps.

Force measurements using Fe-rich amorphous wire as magnetostrictive delay line

In this paper, we present experimental results concerning the heat treatment influence on the force response of Fe 77.5Si 7.5B 15 amorphous wire used as magnetostrictive delay line (MDL). The amorphous wires, 125 μm diameter, were tested in the as-cast state, after stress-relief (thermally treated) and after magnetic annealing. The response of the delay line (pulsed output voltage) could be fitted by a linear curve at certain regions for the case of the as-cast amorphous wires and by an exponential curve for the case of treated wires. The sensitivity is equal to 10 mV/N, the minimum measurable change of the signal being 0.01 mV for the annealed wire corresponding to a minimum change of applied force equal to 0.001 N.

Linear variable differential transformer sensor using Fe-rich amorphous wires as an active core

Results concerning linear variable differential transformer (LVDT) displacement measurements using Fe77.5Si7.5B15 amorphous wires as movable core are presented. Taking advantage of the large Barkhausen (LBE) effect in amorphous wire, a small exciting field and a small number of windings in the secondary coils are necessary to get an large output signal of the LVDT. The thermal noise of the output becomes low, due to the small number of coil turns, increasing thus the sensitivity of the LVDT. The results obtained show a linear dependence of the LVDT response on the displacement of the moving core for displacements up to about 14 mm, with accuracy of 1 μm.

Glass covered Fe-rich amorphous wires used as magnetostrictive delay lines

The operation of Fe-rich glass covered amorphous alloy wires as magnetostrictive delay lines, is illustrated in this paper. These wires cannot demonstrate magnetoelastic wave propagation, since their signal vanishes fast due to the high interlayer stresses between glass coat and magnetic alloy core. We obtained magnetoelastic wave propagation and detection after glass removal and most importantly, after high frequency current annealing without glass removal.

Magneto-optical investigation of micromagnetic structure of Fe-rich amorphous ribbons and wires

The results on the magneto-optical investigation of the magnetization processes and near-surface micromagnetic structure (MMS) of Fe-rich soft magnetic amorphous ribbons and wires are presented. The strong dispersion (in macro- and microscale) of magnetic anisotropy in the studied samples was discovered. In consequence of it, their local magnetic properties were very inhomogeneous. It was proved that magnetization processes of the samples realize by means of incoherent rotation of local magnetization vectors. The buckling and curling modes of the magnetization reversal were observed in ribbons and wires correspondingly. It was established that at a some value of magnetic field the blocking of magnetization processes exists. It was discovered that thermomagnetic annealing of the studied ribbons strongly influence on their local magnetic properties and MMS.

Magnetoelastic behavior of glass-covered amorphous ferromagnetic microwire

Particular aspects concerning the magnetoelastic behavior of an Fe-rich glass-covered amorphous ferromagnetic microwire (diameter about 20 /spl mu/m) are reported in both the as-prepared state and after various heat treatments. The main feature of such behavior is that related with the bistable behavior exhibited by the microwire. The magnetization process takes place by a single and large Barkhausen jump at a given applied field. For the as-prepared material, the value of this switching field (H*/spl ap/112 Am/sup -1/) is about one order of magnitude larger than that reported for Fe-rich amorphous wires with a diameter of about 125 /spl mu/m (H*/spl ap/8 Am/sup -1/). The effect of the thermal treatment as well as the stress dependence of H* for as-obtained and treated microwire are also reported and discussed in terms of the stress distribution within the microwire.