372 research outputs found
Giant magnetoimpedance: new electrochemical option to monitor surface effects?
Magnetoimpedance, MI, change due to surface modification of the sensitive
element caused by biofluids was studied with the aim of creating a robust
sensor capable of separating the chemical surface modification from the sensing
process. A MI sensor prototype with an as-quenched FeCoSiB amorphous ribbon
sensitive element was designed and calibrated for a frequency range of 0.5 to
10 MHz at an intensity of the current of 60 mA. Measurements as a function of
the exposure time were made, first, in a regime where chemical surface
modification and sensing were separated and then, in a regime where they were
not separated (in a bath for fluids). The MI variation was explained by the
change of the surface magnetic anisotropy. It was shown that the
magnetoimpedance effect can be successfully employed as a new electrochemical
option to probe the electric features of surface-modified magnetic electrodes
when the biofluid, the material of the sensitive element, and the detection
conditions are properly selected and synergetically adjusted.Comment: 22 pages, 6 figure
Current distribution and giant magnetoimpedance in composite wires with helical magnetic anisotropy
The giant magnetoimpedance effect in composite wires consising 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 mahnetic material.Comment: 23 pages, 7 figure
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.Comment: 8 pages, 4 figures, publishe
Magnetoimpedance in Symmetric and Non-Symmetric Nanostructured Multilayers: A Theoretical Study
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.This research was funded by the Russian Science Foundation, grant number 18-19-00090
A Model for the Magnetoimpedance Effect in Non-Symmetric Nanostructured Multilayered Films with Ferrogel Coverings
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 detection process by both symmetric and non-symmetric MI structures.This research was funded by the University Basque Country UPV/EHU, Research Groups Funding (IT1245-19)
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