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The correlation between surface domain structure (SDS) and high frequency magneto-impedance (MI) in amorphous microwires has been systematically studied. First, we applied the magneto-optical polarizing microscopy to determine the SDS and found that it is considerably different in unstressed microwire and in microwires to which tensile and torsional stress were applied. Then, we measured the longitudinal and off-diagonal MI in these microwires and also observed quite different MI dependencies. We analyzed the experimental MI curves and their dependence on the SDS with the help of a simple model that nevertheless yields good qualitative agreement with experiment. We have demonstrated that the analysis of the MI dependencies, especially the off-diagonal one, can reveal the SDS in the microwires. The obtained results can also be useful for magnetic and stress sensing applications. [ABSTRACT FROM AUTHOR]

A magnetic field tunable electromagnetic response in periodic lattices of conducting magnetic wires is demonstrated. The wire medium having a negative permittivity in the lower frequency band is customarily investigated as an important component of so-called double negative metamaterials. Here we are interested in a strong dispersion of the permittivity in these structures and a possibility to alter it by changing the losses in magnetic wires with an external magnetic field. The theoretical approach is based on calculating the relaxation parameter depending on the wire surface impedance, and hence, on the wire magnetic properties. Thus, in arrays of Co-based amorphous wires the application of a moderate magnetic field (of about 1-2 kA/m) which causes the magnetization reorientation is capable of few fold permittivity change in the frequency range of 1-2 GHz. Such efficient tuning for certain structural and magnetic parameters was confirmed experimentally by measuring the transmission and reflection spectra from lattices of Co66Fe3.5B16Si11Cr3.5 glass-coated amorphous wires with a different wire cross-section and a different lattice period. The chosen wires are also confirmed to show a large magnetoimpedance effect at GHz frequencies, which constitutes the underlying mechanism of magnetic field dependent permittivity in wire media. [ABSTRACT FROM AUTHOR]

We present systematic studies of the electromagnetic interference (EMI) shielding and microwave properties of a new class of shielding material, i.e., the ferromagnetic microwires-embedded polymer composites. We show that at 1–2 GHz the shielding effectiveness (SE) of the continuous-wire composite reaches a high value of 18 dB (98.4% attenuation) for a very low filler loading of 0.024% and a thickness of 0.64 mm. The normalized SE of this new composite is about 70 times higher than that of the bucky paper-based composite and is two to four orders of magnitude higher than those of other shielding candidate materials. Complex permeability, permittivity, and impedance experiments reveal that the absorption of electromagnetic radiation is a dominant mechanism for EMI shielding of the studied composites. The advantages of high shielding efficiency, good physical integrity, low fabrication costs, and multifunctionalities make them an attractive candidate material for a variety of technological applications. [ABSTRACT FROM AUTHOR]

We report on tailoring the hysteresis loops of arrays containing Fe- and Co-rich microwires utilizing effects of magnetostatic coupling. The interacting wires of both types may produce a complex magnetic response and highly specific spectral characteristics. For Fe-rich microwires we observed step-wise hysteresis loops with a number of Barkhausen jumps equal to a number of Fe-rich microwires. For arrays of Co-based microwires the change in the hysteresis loop shape is less pronounced and is characterized by an increase in the magnetic anisotropy due to interwire interactions. The most interesting multistage magnetization behavior is obtained for arrays containing both types of wires and is characterized by field intervals with both gradual and abrupt magnetization changes. We also investigated the spectral properties associated with each type of magnetization process. The field plots for higher harmonics are highly specific and can be used to discriminate the types of wires in the array. [ABSTRACT FROM AUTHOR]

Two magnetization reversal regimes were found in magnetically bistable Fe-rich microwires. The first one, exhibiting an almost linear dependence of the domain wall velocity v on magnetic field H reaching 1.7 km/s, is related to single DW propagation. The second essentially nonlinear regime is observed when H exceeds some critical magnetic field, HN, determined by the microwire inhomogeneities. At H>HN, new reverse domains can be nucleated, and consequently a tandem remagnetization mechanism can be realized. Ultrafast magnetization switching through additional nucleation centers created artificially can be applied in spintronic devices for enhancing their performance. [ABSTRACT FROM AUTHOR]

Several studies are conducted to explain the various magnetic, mechanical and field tunable properties of the novel glass-coated magnetic microwires-embedded composites. These composites are shown to be widely used in a large number of structural health monitoring and self-sensing applications.

Giant magnetoimpedance (GMI) effect and magnetic properties in ultrathin amorphous glass-coated microwires with nearly zero and negative magnetostruction constant and metallic nucleus are studied. Current annealing has changed off-diagonal MI curves, especially in the case of [Co.sub.74][B.sub.13][Si.sub.11][C.sub.2] microwave.

We report on fabrication and magnetic properties of Heusler-type NiMnInCo glass-coated microwires with metallic nucleus diameters, d, from 13 up to 23 μm and total diameters, D, from 47 to 55 lm by the Taylor-Ulitovsky technique. Considerable dependence of magnetization on magnetic field below and in vicinity of Curie temperature can be related with two-phase structure or with the Hopkinson effect. [ABSTRACT FROM AUTHOR]

We observed different kind of defects, such as gas bubbles, glass coating thickness inhomogeneities, indications of the chemical interaction between the glass shell and the metallic nucleus. We showed that the existence of such bubbles might be the origin of the spontaneous fluctuations of the local nucleation field. [ABSTRACT FROM AUTHOR]

We studied correlation of magnetic properties, giant magnetoimpedance (GMI) effect and structure of Finemet-type glass-coated microwires obtained by the Taylor-Ulitovski technique. We observed considerable magnetic softening and increasing of the GMI ratio, ΔZ/Z, (from 3% up to 100%) after annealing of studied microwires. On the other hand, even in as-prepared Fe73.8Cu1Nb3.1Si13B9.1 microwire, we observed existence of a-Fe nanocrystallites with average grain size about 12 nm and considerable GMI effect (ΔZ/Z up to 50%). [ABSTRACT FROM AUTHOR]

We studied magnetic properties and domain wall propagation in Fe77.5-xNixSi7.5B15 (0⩽x⩽77.5) microwires considering effect of applied and internal stresses. We observed rectangular hysteresis loops and fast domain wall propagation for the Fe77.5-xNixSi7.5B15 (0⩽⩽38.75) microwires. We measured dependences of domain wall velocity on applied magnetic field for the Fe77.5-xNixSi7.5B15 microwires with x⩽38.75. In Fe77.5Si7.5B15 and Fe62Ni15.5Si7.5B15 samples, we observed domain wall velocities up to 2.5 km/s. In all studied samples exhibiting fast domain wall propagation, we observed reduction of domain wall velocity under application of tensile stresses. [ABSTRACT FROM AUTHOR]

We have investigated the effect of dc bias current IB on longitudinal magnetoimpedance (MI) in amorphous microwire with helical anisotropy and experimentally demonstrated that, by changing the dc current IB, it is possible to considerably affect the MI dependence. We propose to use this effect in developing a longitudinal MI sensor that overcomes the drawbacks usually associated with the longitudinal MI-namely the impossibility to determine the direction of an external axial magnetic field HE and the low sensitivity near the zero-field point. We demonstrate that a set of two measurements of longitudinal wire impedance with properly selected bias current IB allows determination of both the magnitude and direction of the magnetic field HE over an extended range, much higher than the sample anisotropy field. Additional features of the proposed method are the increased sensitivity and the detection of exceeding the operating range. [ABSTRACT FROM AUTHOR]

We have prepared Fe-Pt and Fe-Pt- M (M = B, Si) microwires using Taylor-Ulitovsky technique and studied their magnetic properties. Magnetic properties considerably depend on the metallic core composition and annealing conditions. As-prepared microwires present either amorphous or mixture of amorphous and nanocrystalline phases with a presence of BCC FePt, FCC PtFe and small amount of tetragonal FePt phase. After annealing at 500 °C Fe 50 Pt 40 Si 10 microwires we observed a remarkable magnetic hardening (coercivity increasing from 5 Oe up to 500 Oe) related to crystallization of as-prepared amorphous Fe 50 Pt 40 Si 10 microwires. Annealed Fe 50 Pt 50 sample present coercivity up to 800 Oe at 5K, but the magnetization of Fe 50 Pt 50 sample is low and rapidly decreases with temperature. We discussed peculiarity of Fe 50 Pt 50 microwires considering the influence of internal stresses on magnetic ordering of Fe-atoms. [ABSTRACT FROM AUTHOR]