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.

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 nonlinear voltage response in soft magnetic amorphous wires exciting by an alternating current is studied. The frequency spectrum of the voltage in the pick-up coil wound around the wire with a helical anisotropy is found in the framework of a model based on quasi-static Stoner−Wohlfarth magnetization reversal. The effect of a deviation of the anisotropy axis from the azimuthal direction on the field dependences of amplitudes of voltage harmonics is analyzed. It is shown that the field sensitivity of even harmonics increases with the anisotropy axis deviation angle. The current amplitude range to obtain a maximal field sensitivity of the second harmonic is found. The influence of the skin effect on the frequency spectrum of the pick-up coil voltage is discussed. The results obtained may be of importance for the development of sensors of a weak magnetic field.

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 influence of the glass-cover thickness on the magnetoimpedance of amorphous cobalt-based microwires is studied. Microwires with different values of the glass thickness were obtained by etching off the glass cover with fluorhydric acid. It was found that, as the cover thickness decreases, the magnetoimpedance ratio does not substantially change, while the intensity of the external magnetic field in which the impedance attains its maximum also decreases. The experimental results are explained using a model taking into account changes in the radial distribution of the anisotropy axes with a decrease in the glass-cover thickness.

The effect of glass coating thickness on the magneto impedance 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 magnetic field corresponding to the maximum of the impedance decreased with the thickness of the glass layer, whereas the magneto impedance ratio did not change significantly. The experimental results are interpreted in terms of changes in the radial distribution of the easy magnetization axes.

We have studied the response voltage in a coil wound on a glass-coated amorphous microwire, through which an ac current is passed. The amplitudes of the first and second harmonics of the response voltage have been studied as functions of the applied magnetic field. The first harmonic amplitude, which corresponds to a linear off-diagonal magnetoimpedance, is negligibly small, while the second harmonic is highly sensitive to the magnetic field. The behavior of harmonics in the frequency spectrum of the response voltage can be explained by the existence of a regular domain structure in the surface layer of the microwire exposed to a weak magnetic field.

The effect of bias current on the appearance of higher harmonics in the nonlinear mag¬netoimpedance in amorphous wires with a circular anisotropy is studied. The rotational model to calculate the voltage response in the case of a weak skin effect is proposed. It is shown that the ap¬plication of the bias current may lead to significant increase of the second harmonic amplitude in the voltage. The conditions of maximum field sensitivity of the second harmonic are found.

The off-diagonal magnetoimpedance in glass-coated Co-based amorphous microwires is studied using a pick-up coil wound around the sample. The first and second harmonics in the pick-up coil voltage were measured as a function of the external magnetic field. It was observed that the first harmonic in the voltage corresponding to the linear off-diagonal magnetoimpedance was very small. This fact is attributed to the existence of the regular bamboo domain structure within a surface layer of the microwire. On the contrary, the second harmonic in the voltage differed from zero, which is related to the domain-walls motion.

A method for study of a surface magnetic structure in Co-based amorphous microwires with a negative magnetostriction is proposed. The method is based on the off-diagonal magnetoimpedance effect, which can be measured by the pick-up coil wound around the studied sample. The amplitude and phase of the signal in the pick-up coil were analyzed. It was observed that the amplitude and phase did not change at the moving of the pick-up coil along the sample, which denotes the uniform single-domain state at the surface of the studied microwires.

The influence of domain-walls motion on the magnetoinductive response of Co-based amorphous wires having helical anisotropy has been studied. A model describing the domain-walls motion in the field of AC current in the absence of the skin effect is proposed. It is shown that at high enough AC current amplitudes, the domain-walls motion results in the appearance of the second harmonic in the magnetoinductive response. The second harmonic amplitude is studied as a function of the longitudinal external magnetic field, the current frequency and the angle of the deviation of the anisotropy axis from the circular direction for both the voltage across the wire and the pick-up coil voltage. It is demonstrated that the field sensitivity of the second harmonic can be significantly higher than that of the first harmonic.

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.

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.

We used CoFeSiB amorphous wires to investigate the influence of heating and tensile stress on the magneto-impedance value. Measurements were performed with as-cast wires without cover of 100μm diameter and 7mm length. Experiments were carried out at current frequencies 10, 30 and 50MHz, in temperature range from 23 to 180°C.

The effect of a weak ac applied magnetic field on the frequency spectrum of the voltage that appears in a search coil wound around a soft magnetic conductor that carries an alternating current has been studied. In a certain range of ac amplitudes, mixed harmonics having high amplitudes appear in the frequency spectrum of the voltage. This effect is shown to be highly sensitive to the values of a dc applied magnetic field. The experimental results are interpreted in terms of a simple electrodynamic model developed in this work.

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 2f0–f1 (where f0 is the current frequency and f1 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.