Nikita Buznikov - Academia.edu (original) (raw)

Papers by Nikita Buznikov

Research paper thumbnail of High-Frequency Response and Voltage Noise in Magnetic Nanocomposites

Condensed Matter Theories, 2009

We study the noise spectra and high-frequency permeability of inhomogeneous magnetic materials co... more We study the noise spectra and high-frequency permeability of inhomogeneous magnetic materials consisting of single-domain magnetic nanoparticles embedded into an insulating matrix. Possible mechanisms of 1/f voltage noise in phase-separated manganites is analyzed. The material is modelled by a system of small ferromagnetic metallic droplets (magnetic polarons or ferrons) in insulating antiferromagnetic or paramagnetic matrix. The electron transport is related to tunnelling of charge carriers between droplets. One of the sources of the 1/f noise in such a system stems from fluctuations of the number of droplets with extra electron. In the case of strong magnetic anisotropy, the 1/f noise can arise also due to the fluctuations of the magnetic moments of ferrons. The high frequency magnetic permeability of nanocomposite film with magnetic particles in insulating non-magnetic matrix is studied in detail. The case of strong magnetic dipole interaction and strong magnetic anisotropy of ferromagnetic granules is considered. The composite is modelled by a cubic regular array of ferromagnetic particles. The high-frequency permeability tensor components are found as a functions of frequency, temperature, ferromagnetic phase content, and magnetic anisotropy. The results demonstrate that magnetic dipole interaction leads to a shift of the resonance frequencies towards higher values, and nanocomposite film could have rather high value of magnetic permeability in the microwave range.

Research paper thumbnail of Off-Diagonal Magnetoimpedance in Annealed Amorphous Microwires with Positive Magnetostriction: Effect of External Stresses

Magnetism, 2023

It was observed recently that the giant magnetoimpedance (GMI) effect in Fe-rich glass-coated amo... more It was observed recently that the giant magnetoimpedance (GMI) effect in Fe-rich glass-coated amorphous microwires with positive magnetostriction can be improved significantly by means of post-annealing. The increase in the GMI is attributed to the induced helical magnetic anisotropy in the surface layer of the microwire, which appears after the annealing. The application of external stresses to the microwire may result in changes in its magnetic structure and affect the GMI response. In this work, we study theoretically the influence of the tensile and torsional stresses on the off-diagonal magnetoimpedance in annealed amorphous microwires with positive magnetostriction. The static magnetization distribution is analyzed in terms of the core–shell magnetic structure. The surface impedance tensor is obtained taking into account the magnetoelastic anisotropy induced by the external stresses. It is shown that the off-diagonal magnetoimpedance response exhibits strong sensitivity to the magnitude of the applied stress. The obtained results may be useful for sensor applications of amorphous microwires.

Research paper thumbnail of A Model for the Magnetoimpedance Effect in Non-Symmetric Nanostructured Multilayered Films with Ferrogel Coverings

Sensors, 2021

Magnetoimpedance (MI) biosensors for the detection of in-tissue incorporated magnetic nanoparticl... more Magnetoimpedance (MI) biosensors for the detection of in-tissue incorporated magnetic nanoparticles are a subject of special interest. The possibility of the detection of the ferrogel samples mimicking the natural tissues with nanoparticles was proven previously for symmetric MI thin-film multilayers. In this work, in order to describe the MI effect in non-symmetric multilayered elements covered by ferrogel layer we propose an electromagnetic model based on a solution of the 4Maxwell equations. The approach is based on the previous calculations of the distribution of electromagnetic fields in the non-symmetric multilayers further developed for the case of the ferrogel covering. The role of the asymmetry of the film on the MI response of the multilayer–ferrogel structure is analyzed in the details. The MI field and frequency dependences, the concentration dependences of the MI for fixed frequencies and the frequency dependence of the concentration sensitivities are obtained for the d...

Research paper thumbnail of Measurement of magnetic noise in magnetoimpedance sensing element

EPJ Web of Conferences, 2018

A method for measurement of magnetic noise in magnetoimpedance sensing element is pro-posed. Glas... more A method for measurement of magnetic noise in magnetoimpedance sensing element is pro-posed. Glass-coated Co-based amorphous microwires with a slightly negative magnetostriction were used as the sensing element. The operation principle of the sensing element was based on the nonlinear off-diagonal magnetoimpedance, when field dependent higher harmonic components appeared in voltage in the pick-up coil wound around the microwire. The magnetic noise for the second harmonic in the pick-up coil voltage was studied. The dependences of the magnetic noise and the signal-to-noise ratio in the sensitive element on the current amplitude were analyzed. The noise performance of the second harmonic in the pick-up coil voltage was compared to that for a flux-gate sensing element.

Research paper thumbnail of Modeling of magnetoimpedance effect in nanostructured multilayered films

Journal of Physics Conference Series, 2019

The magnetoimpedance effect in nanostructured multilayers is studied theoretically. The multi-lay... more The magnetoimpedance effect in nanostructured multilayers is studied theoretically. The multi-layered film structure consists of highly conductive non-magnetic central layer and two external multilayers containing soft magnetic layers of the same thickness separated either by magnetic spacers of different kind or by non-magnetic spacers. In order to describe the magnetoimpedance in the multilayer an electrodynamic model is proposed. The influence of geometric parameters and physical properties of the layers on the magnetoimpedance response is analyzed. The results obtained could be useful both for better understanding of high-frequency behavior of nanostructured multilayers and for optimization of multilayer parameters aiming to enhance the magnetoimpedance effect for practical applications.

Research paper thumbnail of Magnetoimpedance in Symmetric and Non-Symmetric Nanostructured Multilayers: A Theoretical Study

Sensors, 2019

Intensive studies of the magnetoimpedance (MI) effect in nanostructured multilayers provide a goo... more Intensive studies of the magnetoimpedance (MI) effect in nanostructured multilayers provide a good phenomenological basis and theoretical description for the symmetric case when top and bottom layers of ferromagnet/conductor/ferromagnet structure have the same thickness and consist of one magnetic layer each. At the same time, there is no model to describe the MI response in multilayered films. Here, we propose the corresponding model and analyze the influence of the multilayer parameters on the field and frequency dependences of the MI. The approach is based on the calculation of the field distribution within the multilayer by means of a solution of lineralizied Maxwell equations together with the Landau-Lifshitz equation for the magnetization motion. The theoretical model developed allows one to explain qualitatively the main features of the MI effect in multilayers and could be useful for optimization of the film parameters. It might also be useful as a model case for the development of MI magnetic biosensors for magnetic biomarker detection.

Research paper thumbnail of Influence of Bias Current on Off-Diagonal Magnetoimpedance in Composite Wires

Journal of Superconductivity and Novel Magnetism, 2018

The off-diagonal magnetoimpedance in a composite wire consisting of a highly conductive inner cor... more The off-diagonal magnetoimpedance in a composite wire consisting of a highly conductive inner core covered by a soft magnetic layer is studied theoretically. In the presence of bias current, the field dependence of the off-diagonal magnetoimpedance becomes asymmetric due to the combination of the circular magnetic field produced by the bias current and a helical anisotropy in the magnetic layer of the composite wire. The dependences of the asymmetric off-diagonal magnetoimpedance on the external field, frequency, and bias current are investigated. It is demonstrated that the off-diagonal magnetoimpedance in composite wires has high field sensitivity and exhibits nearly linear behavior at low external fields. The influence of the wire parameters such as the anisotropy axis angle, the magnetic layer thickness, and conductivity on the field sensitivity of the off-diagonal magnetoimpedance is analyzed. The results obtained may be useful for development of weak magnetic-field sensors.

Research paper thumbnail of Asymmetric giant magnetoimpedance effect created by micro magnets

Journal of Magnetism and Magnetic Materials, 2018

Asymmetric giant magnetoimpedance (AGMI) effect has been investigated in as-prepared and current ... more Asymmetric giant magnetoimpedance (AGMI) effect has been investigated in as-prepared and current annealed amorphous (Co0.9Fe0.05Ni0.05)75Si15B10 ribbons. Asymmetry was created by micro magnets. Different numbers of magnets were used and it was found that increasing number of magnet, the shift in AGMI curves increases. When two micro magnets were placed 1 cm away from the ends of ribbon, a distortion in two peak shape of the GMI curve was observed. At high frequency range, a linear change in the AGMI was observed for the current annealed sample.

Research paper thumbnail of Asymmetric Magnetoimpedance in Ferromagnetic Biphase Films: Effects of Magnetostatic Coupling and Number of Layers

Journal of Superconductivity and Novel Magnetism, 2017

A model to describe the asymmetric magnetoimpedance in biphase soft/hard magnetic multilayered fi... more A model to describe the asymmetric magnetoimpedance in biphase soft/hard magnetic multilayered film is proposed. It is shown that a magnetostatic coupling changes the magnetization distribution in soft magnetic layers and leads to asymmetry in the field dependence of the impedance. The influence of the number of the repetitions of the base three-layered film structure having the soft and hard magnetic layers separated by non-ferromagnetic metallic spacer on the asymmetric magnetoimpedance is analyzed. The results of modeling describe main features of the asymmetric magnetoimpedance effect observed in bimagnetic multilayered films. The analysis shows that the multilayers may be attractive for use in miniature sensors of a weak magnetic field.

Research paper thumbnail of A model for asymmetric magnetoimpedance effect in multilayered bimagnetic films

Journal of Magnetism and Magnetic Materials, 2016

The magnetoimpedance in three-layered bimagnetic film structure is studied theoretically. The str... more The magnetoimpedance in three-layered bimagnetic film structure is studied theoretically. The structure consists of the soft and hard magnetic films separated by highly conductive non-magnetic layer. A model to describe the magnetoimpedance effect in the film structure based on a simultaneous solution of linearized Maxwell equations and Landau-Lifshitz equation is proposed. It is shown that magnetostatic coupling between the magnetic layers results in the asymmetry in the field dependence of the film impedance. The magnetostatic coupling is described in terms of an effective bias field appearing in the soft magnetic layer. The calculated field and frequency dependences of the film impedance are shown to be in a qualitative agreement with previous results of experimental studies of the asymmetric magne-toimpedance in NiFe/Cu/Co film structures. The results obtained may be useful for development of weak magnetic-field sensors.

Research paper thumbnail of Asymmetric magnetoimpedance in amorphous microwires due to bias current: Effect of torsional stress

Journal of Magnetism and Magnetic Materials, 2014

The influence of torsional stress on the asymmetric magnetoimpedance in a glass-coated negative m... more The influence of torsional stress on the asymmetric magnetoimpedance in a glass-coated negative magnetostrictive amorphous microwire due to bias current is studied theoretically. The longitudinal and off-diagonal impedance components are found assuming a simplified spatial distribution of the magnetoelastic anisotropy induced by the torsional stress. The asymmetry in the field dependence of the impedance components is attributed to the combination of the circular magnetic field produced by the bias current and a helical anisotropy induced by the torsional stress. The asymmetry in the magnetoimpedance and the low-field hysteresis are analyzed as a function of the bias current and torsional stress. It is shown that the application of torsional stress significantly changes the value of the bias current required to suppress the hysteresis effect. The results obtained may be useful for applications in magnetic-field and stress sensors.

Research paper thumbnail of Effects of helical anisotropy on nonlinear voltage response in amorphous wires

Journal of Magnetism and Magnetic Materials, 2009

The nonlinear voltage response in soft magnetic amorphous wires exciting by an alternating curren... more The nonlinear voltage response in soft magnetic amorphous wires exciting by an alternating current is studied. The frequency spectrum of the voltage in the pickup coil wound around the wire with a helical anisotropy is found in the framework of a model based on quasi-static StonerÀWohlfarth 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 pickup coil voltage is discussed. The results obtained may be of importance for the development of sensors of a weak magnetic field.

Research paper thumbnail of Modeling of torsion stress giant magnetoimpedance in amorphous wires with negative magnetostriction

Journal of Magnetism and Magnetic Materials, 2007

A model describing the influence of torsion stress on the giant magnetoimpedance (GMI) in amorpho... more A model describing the influence of torsion stress on the giant magnetoimpedance (GMI) in amorphous wires with negative magnetostriction is proposed. The wire impedance is found by means of the solution of Maxwell equations together with the LandauÀLifshitz equation, assuming a simplified spatial distribution of the magnetoelastic anisotropy induced by the torsion stress. The impedance is analyzed as a function of the external magnetic field, torsion stress and frequency. It is shown that the magnetoimpedance ratio torsion dependence has an asymmetric shape, with a sharp peak at some value of the torsion stress. The calculated field and stress dependences of the impedance are in qualitative agreement with results of the experimental study of the torsion stress GMI in Co-based amorphous wires.

Research paper thumbnail of Asymmetric off-diagonal magnetoimpedance in field-annealed amorphous ribbons: Analysis of bias current effect

Journal of Magnetism and Magnetic Materials, 2007

The influence of bias current on the asymmetric off-diagonal magnetoimpedance in field-annealed a... more The influence of bias current on the asymmetric off-diagonal magnetoimpedance in field-annealed amorphous ribbons is studied. It is assumed that the ribbon consists of an amorphous bulk and two surface hard magnetic crystalline layers appearing after the annealing. The off-diagonal magnetoimpedance is calculated in the framework of the quasi-static approximation. Without the bias current, the asymmetry in the field dependence of the off-diagonal impedance is related to the exchange coupling between the surface layers and amorphous phase. In the presence of the bias current, the asymmetry results from the interaction between the field induced by the bias current and the exchange coupling bias field. It is shown that the bias current affects significantly the field dependence of the off-diagonal impedance.

Research paper thumbnail of The effect of surface crystalline layers on asymmetric off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons

Journal of Magnetism and Magnetic Materials, 2006

The off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons was measured using ... more The off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons was measured using a pickup coil wound around the sample. One side of a ribbon was etched in hydrofluoric acid solution during various times in order to change the thickness of the surface crystalline layer appearing after annealing. The asymmetric two-peak field dependence of the off-diagonal impedance was observed for all samples. The evolution of the off-diagonal magnetoimpedance with the change in the ribbon thickness is analyzed.

Research paper thumbnail of A model for exchange-biased asymmetric giant magneto-impedance in amorphous wires

Journal of Physics D Applied Physics, 2006

A model describing the exchange-biased asymmetric giant magneto-impedance in Joule-heated amorpho... more A model describing the exchange-biased asymmetric giant magneto-impedance in Joule-heated amorphous wires is proposed. It is assumed that the Joule heating results in the formation of a surface hard magnetic crystalline layer, and the asymmetric giant magneto-impedance is related to the exchange coupling between the amorphous and crystalline phases. The coupling between the surface layer and the amorphous bulk is described in terms of an effective bias field. The model is based on a simultaneous solution of linearized Maxwell equations and the Landau-Lifshitz equation. The calculated field and frequency dependences of the wire impedance are in qualitative agreement with the results of the experimental study of the asymmetric giant magneto-impedance in Joule-heated Co-based amorphous wires.

Research paper thumbnail of Giant magnetoimpedance in composite wires with insulator layer between non-magnetic core and soft magnetic shell

Journal of Magnetism and Magnetic Materials, 2006

A method for calculation of the magnetoimpedance in composite wires having an insulator layer bet... more A method for calculation of the magnetoimpedance in composite wires having an insulator layer between non-magnetic core and soft magnetic shell is described. It is assumed that the magnetic shell has a helical anisotropy and the driving current flows through the core only. The distribution of eddy currents and expressions for the impedance are found by means of a solution of Maxwell equations taking into account the magnetization dynamics within the shell governed by the Landau-Lifshitz equation. The effect of the insulator layer on the magnetoimpedance is analyzed.

Research paper thumbnail of Study of surface magnetic structure in Co-based amorphous microwires by means of off-diagonal magnetoimpedance effect

Journal of Magnetism and Magnetic Materials, 2006

A method for study of a surface magnetic structure in Co-based amorphous microwires with a negati... more 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 pickup coil wound around the studied sample. The amplitude and phase of the signal in the pickup coil were analyzed. It was observed that the amplitude and phase did not change at the moving of the pickup coil along the sample, which denotes the uniform single-domain state at the surface of the studied microwires.

Research paper thumbnail of Current distribution and giant magnetoimpedance in composite wires with helical magnetic anisotropy

Journal of Magnetism and Magnetic Materials, 2006

The giant magnetoimpedance effect in composite wires consisting of a non-magnetic inner core and ... more The giant magnetoimpedance effect in composite wires consisting of a non-magnetic inner core and soft magnetic shell is studied theoretically. It is assumed that the magnetic shell has a helical anisotropy. The current and field distributions in the composite wire are found by means of a simultaneous solution of Maxwell equations and the Landau-Lifshitz equation. The expressions for the diagonal and off-diagonal impedance are obtained for low and high frequencies. The dependences of the impedance on the anisotropy axis angle and the shell thickness are analyzed. Maximum field sensitivity is shown to correspond to the case of the circular anisotropy in the magnetic shell. It is demonstrated that the optimum shell thickness to obtain maximum impedance ratio is equal to the effective skin depth in the magnetic material.

Research paper thumbnail of Off-diagonal magnetoimpedance in field-annealed Co-based amorphous ribbons

Journal of Applied Physics , 2005

The off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons was measured in the... more The off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons was measured in the low-frequency range using a pickup coil wound around the sample. The asymmetric two-peak behavior of the field dependence of the off-diagonal impedance was observed. The asymmetry is attributed to the formation of a hard magnetic crystalline phase at the ribbon surface. The experimental results are interpreted in terms of the surface impedance tensor. It is assumed that the ribbon consists of an inner amorphous region and surface crystalline layers. The coupling between the crystalline and amorphous phases is described through an effective bias field. A qualitative agreement between the calculated dependences and experimental data is demonstrated. The results obtained may be useful for the development of weak magnetic-field sensors.

Research paper thumbnail of High-Frequency Response and Voltage Noise in Magnetic Nanocomposites

Condensed Matter Theories, 2009

We study the noise spectra and high-frequency permeability of inhomogeneous magnetic materials co... more We study the noise spectra and high-frequency permeability of inhomogeneous magnetic materials consisting of single-domain magnetic nanoparticles embedded into an insulating matrix. Possible mechanisms of 1/f voltage noise in phase-separated manganites is analyzed. The material is modelled by a system of small ferromagnetic metallic droplets (magnetic polarons or ferrons) in insulating antiferromagnetic or paramagnetic matrix. The electron transport is related to tunnelling of charge carriers between droplets. One of the sources of the 1/f noise in such a system stems from fluctuations of the number of droplets with extra electron. In the case of strong magnetic anisotropy, the 1/f noise can arise also due to the fluctuations of the magnetic moments of ferrons. The high frequency magnetic permeability of nanocomposite film with magnetic particles in insulating non-magnetic matrix is studied in detail. The case of strong magnetic dipole interaction and strong magnetic anisotropy of ferromagnetic granules is considered. The composite is modelled by a cubic regular array of ferromagnetic particles. The high-frequency permeability tensor components are found as a functions of frequency, temperature, ferromagnetic phase content, and magnetic anisotropy. The results demonstrate that magnetic dipole interaction leads to a shift of the resonance frequencies towards higher values, and nanocomposite film could have rather high value of magnetic permeability in the microwave range.

Research paper thumbnail of Off-Diagonal Magnetoimpedance in Annealed Amorphous Microwires with Positive Magnetostriction: Effect of External Stresses

Magnetism, 2023

It was observed recently that the giant magnetoimpedance (GMI) effect in Fe-rich glass-coated amo... more It was observed recently that the giant magnetoimpedance (GMI) effect in Fe-rich glass-coated amorphous microwires with positive magnetostriction can be improved significantly by means of post-annealing. The increase in the GMI is attributed to the induced helical magnetic anisotropy in the surface layer of the microwire, which appears after the annealing. The application of external stresses to the microwire may result in changes in its magnetic structure and affect the GMI response. In this work, we study theoretically the influence of the tensile and torsional stresses on the off-diagonal magnetoimpedance in annealed amorphous microwires with positive magnetostriction. The static magnetization distribution is analyzed in terms of the core–shell magnetic structure. The surface impedance tensor is obtained taking into account the magnetoelastic anisotropy induced by the external stresses. It is shown that the off-diagonal magnetoimpedance response exhibits strong sensitivity to the magnitude of the applied stress. The obtained results may be useful for sensor applications of amorphous microwires.

Research paper thumbnail of A Model for the Magnetoimpedance Effect in Non-Symmetric Nanostructured Multilayered Films with Ferrogel Coverings

Sensors, 2021

Magnetoimpedance (MI) biosensors for the detection of in-tissue incorporated magnetic nanoparticl... more Magnetoimpedance (MI) biosensors for the detection of in-tissue incorporated magnetic nanoparticles are a subject of special interest. The possibility of the detection of the ferrogel samples mimicking the natural tissues with nanoparticles was proven previously for symmetric MI thin-film multilayers. In this work, in order to describe the MI effect in non-symmetric multilayered elements covered by ferrogel layer we propose an electromagnetic model based on a solution of the 4Maxwell equations. The approach is based on the previous calculations of the distribution of electromagnetic fields in the non-symmetric multilayers further developed for the case of the ferrogel covering. The role of the asymmetry of the film on the MI response of the multilayer–ferrogel structure is analyzed in the details. The MI field and frequency dependences, the concentration dependences of the MI for fixed frequencies and the frequency dependence of the concentration sensitivities are obtained for the d...

Research paper thumbnail of Measurement of magnetic noise in magnetoimpedance sensing element

EPJ Web of Conferences, 2018

A method for measurement of magnetic noise in magnetoimpedance sensing element is pro-posed. Glas... more A method for measurement of magnetic noise in magnetoimpedance sensing element is pro-posed. Glass-coated Co-based amorphous microwires with a slightly negative magnetostriction were used as the sensing element. The operation principle of the sensing element was based on the nonlinear off-diagonal magnetoimpedance, when field dependent higher harmonic components appeared in voltage in the pick-up coil wound around the microwire. The magnetic noise for the second harmonic in the pick-up coil voltage was studied. The dependences of the magnetic noise and the signal-to-noise ratio in the sensitive element on the current amplitude were analyzed. The noise performance of the second harmonic in the pick-up coil voltage was compared to that for a flux-gate sensing element.

Research paper thumbnail of Modeling of magnetoimpedance effect in nanostructured multilayered films

Journal of Physics Conference Series, 2019

The magnetoimpedance effect in nanostructured multilayers is studied theoretically. The multi-lay... more The magnetoimpedance effect in nanostructured multilayers is studied theoretically. The multi-layered film structure consists of highly conductive non-magnetic central layer and two external multilayers containing soft magnetic layers of the same thickness separated either by magnetic spacers of different kind or by non-magnetic spacers. In order to describe the magnetoimpedance in the multilayer an electrodynamic model is proposed. The influence of geometric parameters and physical properties of the layers on the magnetoimpedance response is analyzed. The results obtained could be useful both for better understanding of high-frequency behavior of nanostructured multilayers and for optimization of multilayer parameters aiming to enhance the magnetoimpedance effect for practical applications.

Research paper thumbnail of Magnetoimpedance in Symmetric and Non-Symmetric Nanostructured Multilayers: A Theoretical Study

Sensors, 2019

Intensive studies of the magnetoimpedance (MI) effect in nanostructured multilayers provide a goo... more Intensive studies of the magnetoimpedance (MI) effect in nanostructured multilayers provide a good phenomenological basis and theoretical description for the symmetric case when top and bottom layers of ferromagnet/conductor/ferromagnet structure have the same thickness and consist of one magnetic layer each. At the same time, there is no model to describe the MI response in multilayered films. Here, we propose the corresponding model and analyze the influence of the multilayer parameters on the field and frequency dependences of the MI. The approach is based on the calculation of the field distribution within the multilayer by means of a solution of lineralizied Maxwell equations together with the Landau-Lifshitz equation for the magnetization motion. The theoretical model developed allows one to explain qualitatively the main features of the MI effect in multilayers and could be useful for optimization of the film parameters. It might also be useful as a model case for the development of MI magnetic biosensors for magnetic biomarker detection.

Research paper thumbnail of Influence of Bias Current on Off-Diagonal Magnetoimpedance in Composite Wires

Journal of Superconductivity and Novel Magnetism, 2018

The off-diagonal magnetoimpedance in a composite wire consisting of a highly conductive inner cor... more The off-diagonal magnetoimpedance in a composite wire consisting of a highly conductive inner core covered by a soft magnetic layer is studied theoretically. In the presence of bias current, the field dependence of the off-diagonal magnetoimpedance becomes asymmetric due to the combination of the circular magnetic field produced by the bias current and a helical anisotropy in the magnetic layer of the composite wire. The dependences of the asymmetric off-diagonal magnetoimpedance on the external field, frequency, and bias current are investigated. It is demonstrated that the off-diagonal magnetoimpedance in composite wires has high field sensitivity and exhibits nearly linear behavior at low external fields. The influence of the wire parameters such as the anisotropy axis angle, the magnetic layer thickness, and conductivity on the field sensitivity of the off-diagonal magnetoimpedance is analyzed. The results obtained may be useful for development of weak magnetic-field sensors.

Research paper thumbnail of Asymmetric giant magnetoimpedance effect created by micro magnets

Journal of Magnetism and Magnetic Materials, 2018

Asymmetric giant magnetoimpedance (AGMI) effect has been investigated in as-prepared and current ... more Asymmetric giant magnetoimpedance (AGMI) effect has been investigated in as-prepared and current annealed amorphous (Co0.9Fe0.05Ni0.05)75Si15B10 ribbons. Asymmetry was created by micro magnets. Different numbers of magnets were used and it was found that increasing number of magnet, the shift in AGMI curves increases. When two micro magnets were placed 1 cm away from the ends of ribbon, a distortion in two peak shape of the GMI curve was observed. At high frequency range, a linear change in the AGMI was observed for the current annealed sample.

Research paper thumbnail of Asymmetric Magnetoimpedance in Ferromagnetic Biphase Films: Effects of Magnetostatic Coupling and Number of Layers

Journal of Superconductivity and Novel Magnetism, 2017

A model to describe the asymmetric magnetoimpedance in biphase soft/hard magnetic multilayered fi... more A model to describe the asymmetric magnetoimpedance in biphase soft/hard magnetic multilayered film is proposed. It is shown that a magnetostatic coupling changes the magnetization distribution in soft magnetic layers and leads to asymmetry in the field dependence of the impedance. The influence of the number of the repetitions of the base three-layered film structure having the soft and hard magnetic layers separated by non-ferromagnetic metallic spacer on the asymmetric magnetoimpedance is analyzed. The results of modeling describe main features of the asymmetric magnetoimpedance effect observed in bimagnetic multilayered films. The analysis shows that the multilayers may be attractive for use in miniature sensors of a weak magnetic field.

Research paper thumbnail of A model for asymmetric magnetoimpedance effect in multilayered bimagnetic films

Journal of Magnetism and Magnetic Materials, 2016

The magnetoimpedance in three-layered bimagnetic film structure is studied theoretically. The str... more The magnetoimpedance in three-layered bimagnetic film structure is studied theoretically. The structure consists of the soft and hard magnetic films separated by highly conductive non-magnetic layer. A model to describe the magnetoimpedance effect in the film structure based on a simultaneous solution of linearized Maxwell equations and Landau-Lifshitz equation is proposed. It is shown that magnetostatic coupling between the magnetic layers results in the asymmetry in the field dependence of the film impedance. The magnetostatic coupling is described in terms of an effective bias field appearing in the soft magnetic layer. The calculated field and frequency dependences of the film impedance are shown to be in a qualitative agreement with previous results of experimental studies of the asymmetric magne-toimpedance in NiFe/Cu/Co film structures. The results obtained may be useful for development of weak magnetic-field sensors.

Research paper thumbnail of Asymmetric magnetoimpedance in amorphous microwires due to bias current: Effect of torsional stress

Journal of Magnetism and Magnetic Materials, 2014

The influence of torsional stress on the asymmetric magnetoimpedance in a glass-coated negative m... more The influence of torsional stress on the asymmetric magnetoimpedance in a glass-coated negative magnetostrictive amorphous microwire due to bias current is studied theoretically. The longitudinal and off-diagonal impedance components are found assuming a simplified spatial distribution of the magnetoelastic anisotropy induced by the torsional stress. The asymmetry in the field dependence of the impedance components is attributed to the combination of the circular magnetic field produced by the bias current and a helical anisotropy induced by the torsional stress. The asymmetry in the magnetoimpedance and the low-field hysteresis are analyzed as a function of the bias current and torsional stress. It is shown that the application of torsional stress significantly changes the value of the bias current required to suppress the hysteresis effect. The results obtained may be useful for applications in magnetic-field and stress sensors.

Research paper thumbnail of Effects of helical anisotropy on nonlinear voltage response in amorphous wires

Journal of Magnetism and Magnetic Materials, 2009

The nonlinear voltage response in soft magnetic amorphous wires exciting by an alternating curren... more The nonlinear voltage response in soft magnetic amorphous wires exciting by an alternating current is studied. The frequency spectrum of the voltage in the pickup coil wound around the wire with a helical anisotropy is found in the framework of a model based on quasi-static StonerÀWohlfarth 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 pickup coil voltage is discussed. The results obtained may be of importance for the development of sensors of a weak magnetic field.

Research paper thumbnail of Modeling of torsion stress giant magnetoimpedance in amorphous wires with negative magnetostriction

Journal of Magnetism and Magnetic Materials, 2007

A model describing the influence of torsion stress on the giant magnetoimpedance (GMI) in amorpho... more A model describing the influence of torsion stress on the giant magnetoimpedance (GMI) in amorphous wires with negative magnetostriction is proposed. The wire impedance is found by means of the solution of Maxwell equations together with the LandauÀLifshitz equation, assuming a simplified spatial distribution of the magnetoelastic anisotropy induced by the torsion stress. The impedance is analyzed as a function of the external magnetic field, torsion stress and frequency. It is shown that the magnetoimpedance ratio torsion dependence has an asymmetric shape, with a sharp peak at some value of the torsion stress. The calculated field and stress dependences of the impedance are in qualitative agreement with results of the experimental study of the torsion stress GMI in Co-based amorphous wires.

Research paper thumbnail of Asymmetric off-diagonal magnetoimpedance in field-annealed amorphous ribbons: Analysis of bias current effect

Journal of Magnetism and Magnetic Materials, 2007

The influence of bias current on the asymmetric off-diagonal magnetoimpedance in field-annealed a... more The influence of bias current on the asymmetric off-diagonal magnetoimpedance in field-annealed amorphous ribbons is studied. It is assumed that the ribbon consists of an amorphous bulk and two surface hard magnetic crystalline layers appearing after the annealing. The off-diagonal magnetoimpedance is calculated in the framework of the quasi-static approximation. Without the bias current, the asymmetry in the field dependence of the off-diagonal impedance is related to the exchange coupling between the surface layers and amorphous phase. In the presence of the bias current, the asymmetry results from the interaction between the field induced by the bias current and the exchange coupling bias field. It is shown that the bias current affects significantly the field dependence of the off-diagonal impedance.

Research paper thumbnail of The effect of surface crystalline layers on asymmetric off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons

Journal of Magnetism and Magnetic Materials, 2006

The off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons was measured using ... more The off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons was measured using a pickup coil wound around the sample. One side of a ribbon was etched in hydrofluoric acid solution during various times in order to change the thickness of the surface crystalline layer appearing after annealing. The asymmetric two-peak field dependence of the off-diagonal impedance was observed for all samples. The evolution of the off-diagonal magnetoimpedance with the change in the ribbon thickness is analyzed.

Research paper thumbnail of A model for exchange-biased asymmetric giant magneto-impedance in amorphous wires

Journal of Physics D Applied Physics, 2006

A model describing the exchange-biased asymmetric giant magneto-impedance in Joule-heated amorpho... more A model describing the exchange-biased asymmetric giant magneto-impedance in Joule-heated amorphous wires is proposed. It is assumed that the Joule heating results in the formation of a surface hard magnetic crystalline layer, and the asymmetric giant magneto-impedance is related to the exchange coupling between the amorphous and crystalline phases. The coupling between the surface layer and the amorphous bulk is described in terms of an effective bias field. The model is based on a simultaneous solution of linearized Maxwell equations and the Landau-Lifshitz equation. The calculated field and frequency dependences of the wire impedance are in qualitative agreement with the results of the experimental study of the asymmetric giant magneto-impedance in Joule-heated Co-based amorphous wires.

Research paper thumbnail of Giant magnetoimpedance in composite wires with insulator layer between non-magnetic core and soft magnetic shell

Journal of Magnetism and Magnetic Materials, 2006

A method for calculation of the magnetoimpedance in composite wires having an insulator layer bet... more A method for calculation of the magnetoimpedance in composite wires having an insulator layer between non-magnetic core and soft magnetic shell is described. It is assumed that the magnetic shell has a helical anisotropy and the driving current flows through the core only. The distribution of eddy currents and expressions for the impedance are found by means of a solution of Maxwell equations taking into account the magnetization dynamics within the shell governed by the Landau-Lifshitz equation. The effect of the insulator layer on the magnetoimpedance is analyzed.

Research paper thumbnail of Study of surface magnetic structure in Co-based amorphous microwires by means of off-diagonal magnetoimpedance effect

Journal of Magnetism and Magnetic Materials, 2006

A method for study of a surface magnetic structure in Co-based amorphous microwires with a negati... more 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 pickup coil wound around the studied sample. The amplitude and phase of the signal in the pickup coil were analyzed. It was observed that the amplitude and phase did not change at the moving of the pickup coil along the sample, which denotes the uniform single-domain state at the surface of the studied microwires.

Research paper thumbnail of Current distribution and giant magnetoimpedance in composite wires with helical magnetic anisotropy

Journal of Magnetism and Magnetic Materials, 2006

The giant magnetoimpedance effect in composite wires consisting of a non-magnetic inner core and ... more The giant magnetoimpedance effect in composite wires consisting of a non-magnetic inner core and soft magnetic shell is studied theoretically. It is assumed that the magnetic shell has a helical anisotropy. The current and field distributions in the composite wire are found by means of a simultaneous solution of Maxwell equations and the Landau-Lifshitz equation. The expressions for the diagonal and off-diagonal impedance are obtained for low and high frequencies. The dependences of the impedance on the anisotropy axis angle and the shell thickness are analyzed. Maximum field sensitivity is shown to correspond to the case of the circular anisotropy in the magnetic shell. It is demonstrated that the optimum shell thickness to obtain maximum impedance ratio is equal to the effective skin depth in the magnetic material.

Research paper thumbnail of Off-diagonal magnetoimpedance in field-annealed Co-based amorphous ribbons

Journal of Applied Physics , 2005

The off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons was measured in the... more The off-diagonal magnetoimpedance in field-annealed CoFeSiB amorphous ribbons was measured in the low-frequency range using a pickup coil wound around the sample. The asymmetric two-peak behavior of the field dependence of the off-diagonal impedance was observed. The asymmetry is attributed to the formation of a hard magnetic crystalline phase at the ribbon surface. The experimental results are interpreted in terms of the surface impedance tensor. It is assumed that the ribbon consists of an inner amorphous region and surface crystalline layers. The coupling between the crystalline and amorphous phases is described through an effective bias field. A qualitative agreement between the calculated dependences and experimental data is demonstrated. The results obtained may be useful for the development of weak magnetic-field sensors.