Solid State Phenomena Vols. 152-153

Abstract: The effect of bias current on the appearance of higher harmonics in the nonlinear mag¬netoimpedance in amorphous wires with a circular anisotropy is studied. The rotational model to calculate the voltage response in the case of a weak skin effect is proposed. It is shown that the ap¬plication of the bias current may lead to significant increase of the second harmonic amplitude in the voltage. The conditions of maximum field sensitivity of the second harmonic are found.

Abstract: Microwave permeability of glass-coated ferromagnetic amorphous microwire exhibiting a weak negative magnetostriction has been studied. The diameter of the microwire was about 20 m and the diameter of the metal core was about 12 m. The microwire was wound to comprise a 7/3 washer-shaped composite sample with the volume fraction of magnetic constituent of about 10%. The permeability of the composite sample was measured in a coaxial line in the frequency range from 0.1 to 10 GHz. The composite was found to exhibit a negative permeability within the frequency range from approximately 0.7 to 1.5 GHz, with the permeability being as low as −0.4. Therefore, microwire-based composites, particularly, crossed arrays of microwires may be employed to develop metamaterials for microwave applications. In the composite, the negative microwave permeability is due to the natural ferromagnetic resonance and the negative microwave permittivity is due to the inherent inductance of the wire. Such metamaterials are advantageous in simple design, isotropic in-plane performance, and possible tunability of performance by external magnetic bias. However, for a feasible metamaterial fabricated from microwire arrays, the wires have to exhibit higher magnitude of the ferromagnetic resonance, higher quality factor, and higher resonance frequency.

Abstract: The high frequency intrinsic and effective permeability was calculated for spherical iron and barium particles in a nonmagnetic matrix (epoxy resin) by using the combination of Landau-Lifshitz-Gilbert equation and extended Bruggeman’s effective medium theory with the consideration of the skin effect. It was found that the microwave properties of the composite were influenced by many parameters, such as damping parameter, volume fractions and size of magnetic components. The sandwich microwave absorber with reflection loss < −10 dB over the range of 6-22 GHz was achieved. The thickness of absorber is only 4.25 mm.

Abstract: Circular magnetization processes in electroplated wires is an important topic having straight connection with sensor applications of these soft magnetic materials. In present work the longitudinal and circular hysteresis loops were measured and corresponding magnetization processes were studied in Cu98Be2/Co16Fe20Ni64 wires. The longitudinal hysteresis loops, Mz-Hz, were measured by inductive technique in a frequency range of 10 to 70 Hz. The circular magnetization curves (Mφ- Hφ) were measured for frequencies of 50 and 100 kHz in the Hφ field up to 1500A/m for different values of the axial external field of 0 to 500 A/m. The longitudinal and circular magnetization curves are comparatively analyzed.

Abstract: The spectral properties of magnetostatic waves in a ferromagnet with a moving periodic domain structure are studied within the exchange-free magnetostatic approximation. It is demonstrated that the Doppler frequency shift caused by the domain-wall motion results in the splitting of the spectrum of each magnetostatic wave mode into two dispersion branches―high-frequency and low-frequency branches. It is found that the more the mode number, the more the separation between these branches with respect to the mode spectrum in the presence of the static domain structure. PACS numbers: 75.60.-d, 75.60.Ch, 75.70.Kw

Abstract: Cavity measurements of a high frequency (60 GHz) electron spin resonance (ESR) have been carried our for a single crystal of EuB6 at temperatures 4.2-50K in magnetic field up to 7 T, which has been aligned along [001] crystallographic direction. The influence of the experimental geometry on the parameters of the resonance line has been studied. It is found that in conditions of a homogeneous magnetic field the ESR spectrum in EuB6 is formed by a single resonance line at all temperatures including the ferromagnetic ordering region. The presence of the gradient of the magnetic field in the sample causes strong broadening of the resonance line at low temperatures and even may induce a double peak ESR structure. The analysis of the linewidth temperature dependence in EuB6 shows the anomalous growth of the line width below Curie temperature TC ~15 K.

Abstract: We report results of the study of the recently discovered magnetic resonance in CeB6, which is characteristic to the phase II in the magnetic phase diagram of this strongly correlated heavy fermion metal. Experiments were carried out in a wide frequency range /2=44-360 GHz in magnetic field up to 30 T. It is found that the previously reported magnetic resonance exists at all frequencies studied and the g-factor for this resonance increases with frequency from g(/2=44 GHz)~1.55 to g(/2>250 GHz)~1.7. In addition to the aforementioned mode of magnetic oscillations an additional magnetic resonance with the g-factor 1.2-1.3 is detected for the frequencies exceeding 200 GHz. This effect may be a consequence of a complicated magnetic structure of the phase II, which is not foreseen in the standard models of the low temperature magnetic ordering in CeB6.

Abstract: For inhomogeneous mediums the оptical Magnus effect has been derived. The metamaterials fabricated from amorphous ferromagnet Co-Fe-Cr-B-Si microwires are shown to exhibit a negative refractive index for electromagnetic waves over wide scale of GHz frequencies. Optical properties and optical Magnus effect of such metamaterials are tunable by an external magnetic field.

Abstract: . It is known that bulk metallic samples reflect microwaves (MWs) while metallic powdered samples can absorb such radiation and be heated efficiently. The present paper shows a direct evidence of penetration of MW radiation into and through a layer of metallic powder and contains theoretical explanation of such behavior.

Abstract: Motion of an isolated domain wall in a double-layered magnetic film, whose layers differ in their uniaxial anisotropy only, is investigated through solving the Slonczewski equations by a numerical method. Dependences of the threshold field and the limiting velocity of disruption of the steady state motion of the film on the anisotropy and thicknesses of layers are obtained. Also, we showed that in domain wall unsteady motion regime, a dependence of domain wall velocity from magnetic field contains a series velocity peaks that relies on steady motion of Bloch lines across film and domain wall velocity in such cases can’t be simply increased by increasing magnetic field and restricted by some volume.