The distribution of the magnetic permeability over the cross section of rapidly quenched amorphous Co68.6Fe3.9Mo3.0Si12.0B12.5 ribbons was studied in the range of elastic tensile stresses from 0 to 480 MPa. This distribution was restored using magnetic impedance tomography, which is a method based on the analysis of the frequency dependences of the impedance, when external magnetic fields of varying amplitude or tensile mechanical stresses are applied to ribbons. In this case, the alternating-current frequency varied in the range from 0.01 to 80 MHz.

The results of investigation of the distribution of electrical and magnetic properties over the cross-section are presented for Cu[Formula: see text]Be 2 /Fe[Formula: see text]Co 6 Ni[Formula: see text] composite wire of the “highly conductive core-magnetically soft coating” type, obtained by electrolytic deposition of the FeCoNi layer. Studies performed by the magneto-impedance tomography (MIT) made it possible to determine the specific electrical conductivity of the materials of the core and coating. It was established that the electrodeposited coating had a magnetic structure that was inhomogeneous over the thickness.

The results are presented for the study of the radial distribution of the magnetic permeability of an amorphous Co66Fe4Ta2.5Si12.5B15 wire of 55 μm in radius performed using magnetoimpedance tomography within a range of alternating current frequencies from 0.01 to 100 MHz. It has been found that the value of magnetic permeability strongly depends on a radial coordinate. In this case, the inner regions of the wire are predominantly axially-anisotropic, while the outer layer about 2.5 µm thick is circularly-anisotropic. It has been shown that the magnetoelastic mechanism is not the main one in the formation of magnetic anisotropy in the surface layer of a wire.

The results are presented of the study of the influence of the relaxation annealing at a temperature of 620 K for 2 h on the magnetoimpedance effect (MI) in amorphous Co 66 Fe 4 Nb 2.5 Si 12.5 B 15 wires. It has been found that MI at low ac frequences noticeably increases after heat treatment, while it slightly changes at high frequences. Magnetoimpedance tomography has been used to show that this is related to that the changes in magnetic properties caused by heat treatment are different in various regions of a wire. In this case, the magnetic permeability of the surface region about 2.5 μm thick remains practically unchanged, but that of the inner regions significantly increases after annealing.

The results of a computer simulation and experimental study of the magnetoimpedance effect (MI) in amorphous Co68.5Fe4.0Si15.0B12.5 and Co68.6Fe3.9Mo3.0Si12.0B12.5 ribbons in the ac frequency range from 0.01 to 100 MHz are presented. It was found that the maximum MI value exceeds 200%, which may be of interest in the development of magnetic field sensors. It is also shown that practically significant characteristics of the MI response strongly depend on the ac frequency, which is due to the inhomogeneous distribution of magnetic properties over the ribbon cross section. This distribution was studied using magnetoimpedance tomography based on the analysis of the experimental dependences of the reduced impedance on the ac frequency.

The effect of a constant axial magnetic field on the temperature dependences of the high-frequency electrical impedance of amorphous cylindrical wires of Co66Fe4Nb2.5Si12.5B15 is studied and discussed. In the region of the ferromagnetic phase transition, the action of an axial magnetic field leads to a significant change in the temperature dependence of the impedance measured at frequencies below 10 MHz. The revealed features are explained by the presence of two magnetic phases with different Curie temperatures and different distributions in the bulk of the wire.

Some results are presented for the computer-aided modeling of the frequency dependences of the impedance of a composite highly conductive weakly magnetic strand thin magnetic coating wire. Modeling was performed within a range of alternating current frequencies from 0.01 to 100 MHz in a broad interval of strand and coating specific electroconductivities and coating magnetic permeabilities. Two characteristic frequencies associated with the existence of two areas with different electrical and magnetic parameters, i.e., the strand and the coating were revealed. A convenient method of determining these frequencies is proposed. Modeling results were compared with the experimental frequency dependences of the impedance of a CuBe/FeCoNi composite wire.

A description of the method of magnetoimpedance tomography is presented. This method is based on the analysis of the frequency dependences of the impedance obtained in magnetic fields of various strengths. It allows one to determine the distribution of electrical and magnetic properties over the cross-section of the conductor, as well as their dependence on the magnetic field. The article proposes a specific approach to the implementation of the magnetoimpedance tomography method based on computer modeling by the finite element method. The results of this method are presented for composite Cu98Be2/Fe20Co6Ni74 wires of the “highly conductive core–magnetically soft coating” type and amorphous rapidly quenched Co66Fe4Nb2.5Si12.5B15 wires.

The effect of tensile mechanical stresses and axial magnetic field on the impedance of amorphous Co66Fe4Nb2.5Si12.5B15 wires premagnetized by a circular direct-current magnetic field has been studied. Preliminary circular magnetization leads to appreciable changes in the impedance of wires, and the effect of tensile mechanical stresses and axial magnetic field return the impedance to its initial values. The application of the revealed regularities for the creation of memory strain sensors is proposed.

Thermal reversibility of the magnetoimpedance effect in Co 68.5 Fe 4 Si 15 B 12.5 ribbons is studied. The results obtained are explained taking into account temperature changes in the magnetoelastic properties. Also discussed is the need to take into account the combined effect of temperature and mechanical stresses to address the issues of increasing the thermal reversibility of magnetoimpedance-based sensors.

The temperature dependence of the magnetic impedance of rapidly quenched amorphous ribbons of the Co68.5Fe4Si15B12.5 alloy is studied in the temperature range from 295 to 405 K. It is found that tensile mechanical stresses have a substantial effect on the behavior of the temperature dependence of the impedance. A model that is in good agreement with the experimental results is proposed, which takes into account the temperature changes in the saturation magnetization, the effective magnetic anisotropy constants, the magnetostriction constants, and the dependence of magnetostriction on the mechanical stresses.

Soft magnetic materials are widely requested in electronic and biomedical applications. Co-based amorphous ribbons are materials which combine high value of the magnetoimpedance effect (MI), high sensitivity with respect to the applied magnetic field, good corrosion stability in aggressive environments, and reasonably low price. Functional properties of ribbon-based sensitive elements can be modified by deposition of additional magnetic and non-ferromagnetic layers with required conductivity. Such layers can play different roles. In the case of magnetic biosensors for magnetic label detection, they can provide the best conditions for self-assembling processes in biological experiments. In this work, magnetic properties and MI effect were studied for the cases of rapidly quenched Co67Fe3Cr3Si15B12 amorphous ribbons and magnetic Fe20Ni80/Co67Fe3Cr3Si15B12/Fe20Ni80 composites obtained by deposition of Fe20Ni80 1 μm thick films onto both sides of the ribbons by magnetron sputtering technique. Their comparative analysis was used for finite element computer simulations of MI responses with different types of magnetic and conductive coatings. The obtained results can be useful for the design of MI sensor development, including MI biosensors for magnetic label detection.

Abstract—This work studies the effect of heat treatment on the magnetoimpedance (MI) effect of soft magnetic Co68.5Fe4Si15B12.5 amorphous ribbons prepared by melt quenching on a rotating wheel. It was found that after heat treatments at temperatures of 100°C and higher there occur irreversible changes of MI over a wide range of excitation ac frequencies. A change in the magnetoimpedance response to the action of elastic tensile stresses is shown to be related to the change in the sign of saturation magnetostriction coefficient (λS), which results from the heat treatment.

The influence of magnetic prehistory on the electrical impedance of an amorphous magnetically soft wire composed of Co66Fe4Nb2.5Si12.5B15 is investigated herein. The values of the modulus and components of the wire impedance strongly depend on the strength, direction and sequence of application of magnetic fields used to pre-magnetize the wire. The idea of creating a simple storage element based on an amorphous wire composed of Co66Fe4Nb2.5Si12.5B15 was proposed, in which the intensity of direct current, which previously flowed through the circuit and circularly magnetized the wire, can be determined by its impedance properties. Such an element can be transferred to the initial state via axial magnetic field application. (C) 2019 Elsevier B.V. All rights reserved.

This study investigates the effect of tensile stress on the impedance of an amorphous Co66Fe4Ta2.5Si12.5B15 wire near the magnetostriction compensation temperature at approximately 170 K. When the wire is exposed to the tensile stress, the wire impedance modulus is found to demonstrate high temperature sensitivity of over 2%/K. This finding can help in designing of temperature sensors.

Peculiarities of the structure, magnetic properties, and temperature dependence of magnetoimpedance effect of a Fe20Co6Ni74/Cu98Be2 composite wire with the induced axial magnetic anisotropy are studied in this work. The increase in the temperature in a range from 150 to 450 K is shown to lead to an increase in the magnetoimpedance effect. To explain the experimental results, a model is proposed, which takes temperature variations of the magnetization and magnetic anisotropy constant of the Fe20Co6Ni74 magnetic layer into account.

The temperature dependencies of magnetoimpedance (MI) and stress impedance (SI) were analyzed both in the as-quenched soft magnetic Co68.5Fe4Si15B12.5 ribbons and after their heat treatment at 425 K for 8 h. It was found that MI shows weak changes under the influence of mechanical stresses in the temperature range of 295–325 K and SI does not exceed 10%. At higher temperatures, the MI changes significantly under the influence of mechanical stresses, and SI variations reach 30%. Changes in the magnetoelastic properties for the different temperatures were taken into consideration for the discussion of the observed MI and SI responses. The solutions for the problem of thermal stability of the magnetic sensors working on the principles of MI or SI were discussed taking into account the joint contributions of the temperature and the applied mechanical stresses.