A. L. Rakhmanov

Magnetization reversal process and nonlinear magneto-impedance in Cu/NiFe and Nb/NiFe composite wires

The magnetization reversal of Cu/NiFe and Nb/NiFe composite wires carrying AC current is studied. The frequency spectrum of a voltage induced in a pick-up coil wound around the wire is analyzed. The frequency spectrum is shown to consist of even harmonics within a wide range of AC current amplitudes and longitudinal DC magnetic fields. The strong dependencies of the harmonic amplitudes on the DC field are found. The results obtained may be of importance for the design of weak magnetic field sensors.

Magnetic properties and magneto-impedance of cold-drawn permalloy-copper composite wires

The permalloy-copper composite wires consisting of high conductivity Cu inner core and NiFe outer shell were fabricated by a modified cold-drawn technique, The diameter of the Cu inner core was in 20-120 /spl mu/m range, and the NiFe outer shell was 10-40 /spl mu/m thick. The composite wires exhibit soft magnetic behavior and the giant magneto-impedance effect. The amplitude of the giant magneto-impedance at high frequencies is comparable to that of conventional amorphous wires and significantly larger than that of NiFe wires without Cu inner core. Nevertheless, the sensitivity of these wires does not reach the theoretical predictions based on the simple models for composite wires with the axial or circumferential types of magnetic anisotropy.

Domain-walls motion in glass-coated CoFeSiB amorphous microwires

A method for observation of domain-walls motion in amorphous microwires with circular magnetic anisotropy is proposed. Using the method, the magnetization reversal of glass-coated Co-based microwires induced by current pulses of high amplitude is studied. The magnetization reversal is shown to occur due to the nucleation of the domain walls at the sample ends and their subsequent motion along the microwire. The dependencies of the domain-wall velocity on the current pulse amplitude and a longitudinal DC magnetic field are measured. A model describing main features of experimental data is presented.

Dynamic permeability of ferromagnetic thin films with stripe domain structure

Summary form only given. A relationship constraining the static permeability and resonance frequency of thin ferromagnetic films has been established recently. This relationship is great importance in view of the problem of developing the materials possessing high permeability at microwaves. But the relationship is of limited applicability, being derived for a single domain film with uniaxial inplane anisotropy only. This paper deals with more practical occasion, where the effect of the stripe domain structure and of out-of-plane magnetic anisotropy on the dynamic permeability of a ferromagnetic thin film.

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.

Remagnetization of a circularly anisotropic amorphous wire in an alternating magnetic field

Remagnetization of an amorphous ferromagnetic wire with circular anisotropy in an alternating longitudinal magnetic field was theoretically studied within the framework of a quasistationary approximation. A frequency spectrum of the emf generated in a probing coil wound on the wire was determined, and analytical expressions describing the dependence of the emf amplitude on the alternating magnetic field amplitude H0 and the constant magnetic bias field value He were derived. The results can be applied to the development of weak magnetic field sensors.

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.

Nonlinear magnetization reversal in copper-permalloy composite wires induced by a high-frequency current

The phenomenon of magnetization reversal in copper-permalloy composite wires induced by a high-frequency ac current field was studied. The frequency spectrum of a voltage measured in the probing coil wound on the wire contains only even harmonics in a broad range of amplitudes of the ac excitation current and the bias magnetic field strength. The amplitude of the even harmonics measured is highly sensitive with respect to the bias field. The results can be used to develop weak magnetic field sensors.

The influence of moving domain walls on the appearance of the second harmonic in the magnetoimpedance spectrum of a cobalt-based amorphous microwire

We have studied the influence of moving domain walls (DWs) on the magnetoimpedance of a cobalt-based amorphous microwire. A model describing the DW motion in the electric field of an alternating current in the absence of a skin effect is proposed. When the current amplitude exceeds a certain threshold value, the DW motion leads to the appearance of a second harmonic component in the frequency spectrum of the sample response voltage. The second harmonic amplitude has been studied as a function of the external longitudinal magnetic field, the current frequency, and the angle of deviation of the microwire anisotropy axis from the circular direction. The sensitivity of the second harmonic to the external magnetic field can be significantly higher than that of the first harmonic.

Magnetization reversal process and nonlinear magnetoimpedance in multilayered films

The AC current induced magnetization reversal of a three-layered film structure consisting of soft magnetic outer layers and a nonmagnetic inner layer is studied. The frequency spectrum of the voltage induced in the pick-up coil wound around the sample is analyzed. A high sensitivity of the voltage response to an external DC magnetic field is demonstrated. The results obtained may be of importance for the design of miniature sensors of a weak magnetic field.