A.N. Shalygin

Behaviour of erythrocytes in high gradient magnetic field

Abstract To obtain magnetic characteristics of single biological cells in vivo behaviour of human erythrocytes has been investigated in single wire high gradient magnetic separator (HGMS) experiments. Phenomenon of diamagnetic capture in the field reduction region near transversely magnetized wire has been discovered for erythrocytes with oxyhemoglobin. The trajectories of erythrocytes were observed in single wire HGMS experiments in paramagnetic and diagmagnetic modes of motion. The values of susceptibility of individual erythrocytes in various states were estimated.

The Faraday Effect in Garnets in the Infrared Region

The temperature dependence of the Faraday effect in TbIG was investigated in the infrared where the rotation αφ does not depend on frequency. It was shown that besides the change in the sign of αφ at the compensation point, there is another change in the sign of αφ at T = 110°K. The temperature dependence of αφ agrees qualitatively with its theoretical behavior obtained in the infrared region from the off‐diagonal components of permeability tensor [μ]. For the quantitative agreement of the theoretical and experimental values of αφ, it is necessary to assume that the g‐factor of Tb3+ diminishes at low temperatures. The temperature dependence of the g‐factor of the Tb3+ ion in TbIG was determined, It was shown that in Bi0.24Ca2.76Fe3.62V1.38O12 at λ > 4 μ the Faraday effect is positive and independent of λ. The Faraday effect in the garnet has different signs in the infrared and visible regions. This fact is in accordance with the exchange mechanism of the Faraday effect observed in garnets in the infrared.

The Influence of Quantum Size Effects on Magnetic Properties of Thin-Film Systems

Results on the investigation of magnetic and magneto-optical properties of Fe/NML/Fe (NML: Mo, Ta) thin-film systems are presented. The examined samples were prepared by DC magnetron sputtering technique. The hysteresis loops and spectral dependencies of the transverse Kerr effect (TKE) were measured employing the magneto-optical magnetometer and the magneto-optical spectrometer, respectively. The saturation field of the examined trilayers was revealed to oscillate as a function of the NML layer thickness, and the period of these oscillations to depend on the Fe layer thickness. The TKE spectra of the studied systems were found to be identical but the TKE values depend on the thickness of both Fe and Mo, Ta layers.

Specific features of magnetic properties of “thick” microwires produced by the Ulitovsky-Taylor method

The magnetic properties of initial and heat-treated Co69Fe4Cr4Si12B11 microwires in a glass shell with the diameter D = 125 μm and the diameter of the amorphous metallic core d = 90 μm produced by the Ulitovsky-Taylor method have been studied. It has been found that the magnetic characteristics, in particular, the saturation field HS and the coercive force HC of the samples annealed at a temperature T < 300°C do not differ from HS and HC of the initial microwire, and those of the samples annealed at T ≥ 400°C increase by almost one order of magnitude. The obtained experimental data have been explained by the structural features of the microwires. The near-surface values of HS and HC at T < 300°C are found to be larger than the bulk values by a factor of 5–10. These experimental data have been explained by the existence of structural and chemical ingomogeneities in the near-surface layer, which are inherent in amorphous materials. This difference decreases with a further increase in the annealing temperature, but HS and HC increase substantially. This fact has been explained by the beginning of the microwire crystallization.

Image analysis of bioparticles accumulation and diamagnetic alignment in high-gradient magnetic field

Magnetic properties of biological particles are measured in high-gradient magnetic separation (HGMS) analysis, revealing the concentrating process of nucleoprotein particles, ferritin, red blood cells, and eggs. A magnetic force acting on micrometer and submicrometer biological particles having diamagnetic or paramagnetic susceptibility with respect to the solution causes their movement and accumulation in gradient magnetic fields dependent on the values of the magnetic moments. The methods developed enable us to obtain the magnetic moments values of single particles and their assembly directly from magnetic separation and image analyses without assuming the detection of sizes. Our precision methods for the measurement of the capture traveling (magnetic diffusion) time and the accumulation (magnetic sedimentation) radius in HGMS show that it is really possible to determine the weak dia- or paramagnetic shifts of magnetic susceptibility up to 0.7x10(-10) (SI units). HGMS analysis of the concentrating process of nucleoprotein granules (microcells, DNA granules, or nucleosome core particles) with polarization microscopy reveals phase transitions for DNA in granules, and separation accumulation of particles enables the determination of the diamagnetic susceptibility and anisotropy properties. Magnetic concentration effects always occur in living systems because micrometer-located gradient magnetic fields inside an organism are strong enough to cause drifts of cellular complexes and organelles of micrometer and submicrometer sizes. We report the appearance of superparamagnetic contamination inside developing shrimp eggs. In the developing shrimps eggs, ferritin aggregates are observed under weak gradient magnetic fields and diaparaferromagnetic changes are detected. A significant interruption of egg development is revealed in such fields.

Determination of sendust intrinsic permeability from microwave constitutive parameters of composites with sendust spheres and flakes

Intrinsic permeability of sendust alloys is determined from the measured microwave permittivity and permeability of composites filled with either spherical or flaky sendust powders. The permittivity and permeability measurements are performed applying the coaxial reflection-transmission technique in the 0.05 to 18 GHz frequency range. The effects of the filling factor, inclusion shape, and size on composite constitutive parameters are discussed. The permeability of metal inclusion is retrieved from the measured permeability of composites using a generalized Maxwell Garnett equation that accounts for the percolation threshold. The equation parameters are found by fitting the measured dependence of composite permittivity and permeability on frequency and filling. The inclusion dimensions calculated from the found parameters agree with the results of grain-size analyses. The alloy intrinsic permeability is retrieved from inclusion permeability with the account for skinning. The fitted frequency and damping f...

Influence of quantum confinement on magnetic properties of Fe/Mo/Fe and Fe/Ta/Fe thin-film systems

The magnetic properties of Fe/NML/Fe thin-film structures with Mo and Ta non-magnetic layers (NMLs) grown by magnetron sputtering have been studied using magnetooptical techniques. It is established that the saturation field (HS) of the samples exhibits oscillations as a function of the NML thickness (tNML) and the period of oscillations depends on the thickness of iron layers. This behavior of HS(tNML) is explained by the oscillatory character of exchange coupling between the ferromagnetic layers.

Magneto-Optical Investigation of Thin-Film Magnetic Systems

Results on the investigation of magnetic and magneto-optical properties of nanocrystalline Fe/Zr and Fe/Zr, Mo/Fe thin-film systems are presented. The examined samples were prepared by DC magnetron sputtering technique. The structural investigations of the samples were performed by X-ray diffraction analysis. The hysteresis loops and spectral dependencies of the transverse Kerr effect were measured employing the magneto-optical magnetometer and the magneto-optical spectrometer, respectively. The influence of the Zr and Mo layer thickness on the magnetic and magneto-optical properties of the examined samples was observed.

Metamaterials Fabricated of Amorphous Ferromagnetic Microwires: Negative Microwave Permeability

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.

Magnetic properties of thin-film Co/Fe/Ni magnetic systems

The magnetic properties of Co/Fe/Ni thin-film structures grown by magnetron sputtering have been studied using magnetooptical techniques. The results of x-ray diffraction measurements showed that all samples possessed a nanocrystalline structure. The magnetization curves and hysteresis loops were measured using the equatorial Kerr effect for two orientations of the external magnetic field. It is established that the Co/Fe/Ni thinfilm structures exhibit a planar magnetic anisotropy. The magnetic behavior of each layer in the initial inhomogeneous Co/Fe/Ni structure is substantially influenced by stray fields of the adjacent layers. This circumstance accounts for the complex shapes of hysteresis loops. The annealing in vacuum at T = 500°C renders Co/Fe/Ni thin-film structures magnetically hard compared to the initial state. The experimental results are explained by certain features of the microstructure of samples.