A.A. Rakhmanov

The thermal and stress effect on GMI in amorphous wires

We report results on the magneto-impedance (MI) effect in CoFeSiB amorphous wires with and without glass cover and a composite wire under heating up to about 180°C which is much less than the crystallisation one and internal longitudinal stresses. The changing of the MI effect with low-temperature heating was irreversible and strongly depended on the processing environment.

Nonlinear magnetoimpedance effect in soft magnetic amorphous wires extracted from melt

The nonlinear mode of the magnetoimpedance in Co-based amorphous wires extracted from the melt is studied. The frequency spectrum of a voltage induced in a pick-up coil wound around the wire is analyzed as a function of an ac current amplitude and a longitudinal dc magnetic field. It is observed that at sufficiently high ac current amplitudes even harmonics dominate in the pick-up voltage spectrum. A high sensitivity of even harmonics to the dc magnetic field is demonstrated. The studied nonlinear magnetoimpedance is promising for the design of weak magnetic field sensors.

Effect of torsional stresses on the magnetoimpedance of amorphous wires with negative magnetostriction

A model to describe the effect of torsional stresses on the magnetoimpedance of amorphous wires with negative magnetostriction is suggested. An approximate expression for the impedance with regard to the spatial distribution of magnetoelastic anisotropy induced by torsional stresses is derived. It is shown that the relative variation of the impedance is maximal near a critical stress value at which the surface magnetic structure of the wire changes. The calculated dependences of the impedance on the external magnetic field and torsional stress are in good qualitative agreement with experimental data for amorphous wires with negative magnetostriction.

The effect of external magnetic field on the remagnetization process in FeCuNbSiB/Al/FeCuNbSiB films induced by an alternating current

The alternating current induced remagnetization process in FeCuNbSiB/Al/FeCuNbSiB films is studied. The frequency spectra of the voltage arising in the pick-up coil wound around the sample are measured as a function of an external dc magnetic field. It is shown that the frequency spectra differ substantially for the transverse and longitudinal external magnetic field directions. For the transverse field, several harmonics have high amplitudes, whereas for the longitudinal field, even harmonics dominate in the frequency spectrum. A high field sensitivity of the voltage response is demonstrated. The experimental results are interpreted within the framework of a simple rotational model.

Effects of longitudinal AC magnetic field on frequency spectrum of voltage response of soft magnetic conductors

Abstract The effect of superimposed AC and DC longitudinal magnetic fields on the frequency spectrum of a voltage arising in the pick-up coil wound around a soft magnetic conductor carrying AC current is studied. It is observed that the amplitude of the combination harmonic with the frequency 2 f 0 – f 1 (where f 0 is the current frequency and f 1 is the AC magnetic field frequency) increases sharply within some range of the AC current amplitudes. It is demonstrated that the combination harmonic amplitude is sensitive to the DC magnetic field. The experimental results are interpreted in the framework of the quasi-static approximation.

Effect of direct current on higher harmonic generation in the frequency spectrum of magnetoimpedance of amorphous wires with circular anisotropy

The effect of direct current on the nonlinear response of magnetoimpedance in circularly anisotropic amorphous wires is investigated. A model is proposed for calculating the voltage across the ends of the wire in the case of a weak skin effect in the sample. It is shown that a direct current passing through the wire can substantially increase the amplitude of even harmonics of the voltage. The conditions in which the sensitivity of the second harmonic to the applied magnetic field is maximal are determined.

The frequency spectrum of a voltage measured in an amorphous wire magnetized in alternating magnetic field

We have studied the process of magnetization reversal in amorphous microwires under the action of a longitudinal (axial) high-frequency magnetic field. The amplitudes of harmonics in the frequency spectrum of the response voltage between the wire ends were measured as functions of the high-frequency field amplitude and a dc axial magnetic field strength. For relatively large amplitudes of the high-frequency field, the first several harmonics in the frequency spectrum of the response voltage are highly sensitive with respect to the dc magnetic field. The experimental results are interpreted within the framework of a simple electrodynamic model.

Frequency spectrum of the nonlinear magnetoimpedance of multilayer film structures

Magnetization reversal by high-frequency current in FeCuNbSiB/Al/FeCuNbSiB three-layer film structures is studied. The frequency spectrum of the voltage arising in a coil wound on the sample as a function of a permanent magnetic field (nonlinear magnetoimpedance) is taken. It is shown that the frequency spectra of the voltage are qualitatively different for the longitudinal and transverse orientations of the field with respect to the direction of the current. Frequency spectrum harmonics are demonstrated to be highly sensitive to a magnetic field. A simple electrodynamic model to describe experimental data is suggested.

Amplification of even Harmonics in Nonlinear Magnetoimpedance Response of Amorphous Wires in Presence of Longitudinal Alternating Magnetic Field

A model to describe the influence of longitudinal alternating magnetic field on the nonli-near magnetoimpedance in amorphous wires is proposed. The appearance of even harmonics in the voltage response is shown to arise from the asymmetry in the magnetization reversal process in the wire due to the presence of the longitudinal alternating field. The behavior of even harmonics is analyzed as a function of the external field, alternating field amplitude and current amplitude.

Influence of Glass Coating Thickness on Magnetoimpedance Ratio in Co-Based Amorphous Microwires

The effect of glass coating thickness on the magnetoimpedance in Co-based amorphous microwires was studied. The microwires with different thickness of the glass layer were obtained by means of etching in hydrofluoric acid solution. It was observed that the value of the external mag¬netic field corresponding to the maximum of the impedance decreased with the thickness of the glass layer, whereas the magnetoimpedance ratio did not change significantly. The experimental results are interpreted in terms of changes in the radial distribution of the easy magnetization axes.