Magnetoimpedance of CoFeCrSiB Ribbon-Based Sensitive Element with FeNi Covering: Experiment and Modeling

Theoretical Study of Microwires with an Inhomogeneous Magnetic Structure Using Magnetoimpedance Tomography

The recently proposed magnetoimpedance tomography method is based on the analysis of the frequency dependences of the impedance measured at different external magnetic fields. The method allows one to analyze the distribution of magnetic properties over the cross-section of the ferromagnetic conductor. Here, we describe the example of theoretical study of the magnetoimpedance effect in an amorphous microwire with inhomogeneous magnetic structure. In the framework of the proposed model, it is assumed that the microwire cross-section consists of several regions with different features of the effective anisotropy. The distribution of the electromagnetic fields and the microwire impedance are found by an analytical solution of Maxwell equations in the particular regions. The field and frequency dependences of the microwire impedance are analyzed taking into account the frequency dependence of the permeability values in the considered regions. Although the calculations are given for the case of amorphous microwires, the obtained results can be useful for the development of the magnetoimpedance tomography method adaptation for different types of ferromagnetic conductors.

Magnetoimpedance Effect in Cobalt-Based Amorphous Ribbons with an Inhomogeneous Magnetic Structure

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.

Longitudinal Spin Seebeck Effect Thermopiles Based on Flexible Co-Rich Amorphous Ribbons/Pt Thin-Film Heterostructures

Thermoelectric phenomena, such as the Anomalous Nernst and Longitudinal Spin Seebeck Effects, are promising for sensor applications in the area of renewable energy. In the case of flexible electronic materials, the request is even larger because they can be integrated into devices having complex shape surfaces. Here, we reveal that Pt promotes an enhancement of the thermoelectric response in Co-rich ribbon/Pt heterostructures due to the spin-to-charge conversion. Moreover, we demonstrated that the employment of the thermopiles configuration in this system increases the induced thermoelectric current, a fact related to the considerable decrease in the electric resistance of the system. By comparing present findings with the literature, we were able to design a flexible thermopile based on LSSE without the lithography process. Additionally, the thermoelectric voltage found in the studied flexible heterostructures is comparable to the ones verified for rigid systems.

Anomalous Nernst Effect in Flexible Co-Based Amorphous Ribbons

Fe3Co67Cr3Si15B12 ribbons with a high degree of flexibility and excellent corrosion stability were produced by rapid quenching technique. Their structural, magnetic, and thermomagnetic (Anomalous Nernst Effect) properties were studied both in an as-quenched (NR) state and after stress annealing during 1 h at the temperature of 350 °C and a specific load of 230 MPa (AR). X-ray diffraction was used to verify the structural characteristics of our ribbons. Static magnetic properties were explored by inductive technique and vibrating sample magnetometry. The thermomagnetic curves investigated through the Anomalous Nernst Effect are consistent with the obtained magnetization results, presenting a linear response in the thermomagnetic signal, an interesting feature for sensor applications. Additionally, Anomalous Nernst Effect coefficient SANE values of 2.66μV/K and 1.93μV/K were estimated for the as-quenched and annealed ribbons, respectively. The interplay of the low magnetostrictive properties, soft magnetic behavior, linearity of the thermomagnetic response, and flexibility of these ribbons place them as promising systems to probe curved surfaces and propose multifunctional devices, including magnetic field-specialized sensors.

The Study of the Distribution of Electrical and Magnetic Properties over the Conductor Cross-Section Using Magnetoimpedance Tomography: Modeling and Experiment

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 Co₆₆Fe₄Nb_2.5Si_12.5B₁₅ wires.

Amorphous FeCoCrSiB Ribbons with Tailored Anisotropy for the Development of Magnetic Elements for High Frequency Applications

The ferromagnetic resonance (FMR) in the frequency range of 0.5 to 12.5 GHz has been investigated as a function of external magnetic field for rapidly quenched Fe₃Co₆₇Cr₃Si₁₅B₁₂ amorphous ribbons with different features of the effective magnetic anisotropy. Three states of the ribbons were considered: as-quenched without any treatment; after relaxation annealing without stress at the temperature of 350 °C during 1 h; and after annealing under specific stress of 230 MPa at the temperature of 350 °C during 1 h. For FMR measurements, we adapted a technique previously proposed and tested for the case of microwires. Here, amorphous ribbons were studied using the sample holder based on a commercial SMA connector. On the basis of the measurements of the reflection coefficient S_11, the total impedance including its real and imaginary components was determined to be in the frequency range of 0.5 to 12.5 GHz. In order to confirm the validity of the proposed technique, FMR was also measured by the certified cavity perturbation technique using a commercial Bruker spectrometer operating at X-band frequency of 9.39 GHz. As part of the characterization of the ribbons used for microwave measurements, comparative analysis was performed of X-ray diffraction, optical microscopy, transmission electron microscopy, inductive magnetic hysteresis loops, vibrating sample magnetometry, magneto-optical Kerr effect (including magnetic domains) and magnetoimpedance data for of all samples.