Ondřej Životský

Magneto-optic vector magnetometry of CoFeCrSiB amorphous ribbons

A magneto-optic method suitable for investigation of soft magnetic ribbons is proposed that combines the internal magnetic field induced by a current flowing through the ribbon axis with the external magnetic field generated by an air coil. The method eliminates effects of demagnetizing factor and shape anisotropy on measured hysteresis loops. Both in-plane magnetization components are measured by means of magneto-optic vector magnetometry. The method is applied to study magnetic properties of CoFeCrSiB amorphous ribbons showing asymmetric giant magnetoimpedance effects. A coherent rotation of magnetization and in-plane easy axis inclined from the ribbon axis is observed. It corresponds to helical magnetic anisotropy originating from the preparation processes.

Magneto-optic material selectivity in self-assembled BiFeO3–CoFe2O4 biferroic nanostructures

Material selective sensitivity of a magneto-optical polar Kerr effect to magnetic contributions from different inclusions in self-organized magnetic nanostructures is presented. The method is supported by modeling of the magneto-optic response based on the effective medium approximation and by hysteresis loop measurement of the multiferroic BiFeO3–CoFe2O4 self-assembled nanostructure. Magneto-optic selective sensitivity is demonstrated and explained as an effect of different complex diagonal and off-diagonal permittivity tensor elements of two materials.

Composite Fe3O4/Humic Acid Magnetic Sorbent and its Sorption Ability for Chlorophenols and some other Aromatic Compounds

A composite magnetic sorbent with a relatively high content of humic substances (above 35% of organic carbon) was prepared by co-precipitation of Fe2+/Fe3+ salts with commercially available alkaline humate concentrate. Magnetite (Fe3O4) was identified as the main crystalline phase bearing the magnetic properties of the sorbent. Scanning electron microscope (SEM) images revealed the presence of uniform sub-micron structures on the surface of the sorbent grains. Due to the presence of humic substances, the sorbent exhibited good sorption ability towards low-polarity organic pollutants, namely chlorophenols. The sorption efficiency increased in the order of 4-mono- < 2,4-di- < 2,4,5-trichlorophenol in accordance with growing hydrophobicity of these compounds, confirming a hydrophobic nature of the interactions involved in the sorption process. Similar trends were found in the desorption study utilizing water and methanol as leachants. Some polycyclic aromatic hydrocarbons (naphthalene, anthracene, phenanthrene, fluoranthene, pyrene) were also retained on the sorbent. The chemical composition as well as the main physical characteristics (surface area, phase composition) of the sorbent remained virtually unchanged during the sorption process. The sorbent retained its magnetic properties during the sorption of organic substances from aqueous solutions, which provides an opportunity for its regeneration.

A shape optimization method for nonlinear axisymmetric magnetostatics using a coupling of finite and boundary elements

AbstractIn this paper we propose a method for constrained shape optimization governed with a nonlinear axisymmetric magnetostatic state problem and we apply it to an optimal shape design of an electromagnet. The state problem is solved via Hiptmairs symmetric coupling of finite elements employed in the interior ferromagnetic domain and boundary elements modelling the exterior air domain as well as current excitations. As a novelty we derive Duffy regularization transforms of the boundary element integrals for the axisymmetric case, which are then evaluated using a tensor-product Gaussian quadrature. Nonlinear ferromagnetic behaviour is resolved by Newton iterations. The optimization method under both linear and nonlinear constraints relies on the active-set steepest-descent search, projections onto the set of linearized constraints, and an adjoint method of shape sensitivity analysis. Shape perturbations influence grid deformation via a solution to an auxiliary torsion-free linear elasticity problem. Finally, numerical results are presented.

Optical spectroscopy of terbium-scandium-aluminium garnet and terbium-scandium perovskite

Tb3Sc2Al3O12-TbScO3 eutectic crystallizes in a rodlike microstructure, and its potential to exhibit photonic bandgap has been presented tentatively. In order to model its optical properties there is a need for precise determination of the optical properties of its component materials in a wide spectral range. Spectroscopic data in the range from 0.6 to 6.5 eV (190-2100 nm) were obtained using spectroscopic ellipsometer UVISEL, Horiba Jobin-Yvon. The measurement was completed with mid infrared reflection data using Bruker FTIR spectrometer in the spectral range from 7500 to 550 cm-1. Optical functions were obtained using fitting of the data with model dielectric function fulfilling the Kramers-Kronig dispersion relations. Obtained optical functions enable to model the optical properties of self-organized eutectic micro- and nanostructures.

Total internal reflection ellipsometry of periodic structures

The theoretical model of the evanescent waves coupling with dielectric and metallic strip gratings is described. The interaction of electromagnetic field with lamellar periodic structures and their diffraction properties are determined by coupled wave method implemented as the Fourier modal method. The simulations of the ellipsometric response under internal reflection for different geometrical and material configurations are presented. The attention is concentrated on the study of coupling strength influence, effects connected with stripes geometry, and, with absorption in metallic elements of grating.

Influence of Magnetostriction on Cross-Sectional Magnetic Properties in Bilayered Ribbons

This paper is devoted to the surface and cross-sectional microstructural and magneto-optical investigations of the bilayered (BL) CoFeCrSiB-based ribbon of dissimilar Co/Fe content in the layers and to the comparison with the CoSiB/FeSiB ribbon, both prepared by planar flow casting. It is shown that the interface properties are strongly influenced by chemical compositions of the layers and mainly by the magnetostriction coefficients. This results in different magnetic domain patterns in the layers and across the interlayer and their changes with applied magnetic field intensity. While in the BL sample of a similar layer composition, the magnetic domains concentrate inside the layers, at the sample with completely different layer composition, the domains cross the interlayer.

Ferromagnetic nanoparticular films studied by optical and magneto-optical ellipsometry

Fe and Co nanoparticles embedded in SiO2 matrix were prepared using dual radiofrequency magnetron sputtering. Films were characterized by high resolution transmission electron microscopy (HRTEM). Magnetic properties were measured using longitudinal magneto-optical Kerr effect. Magneto-optical hysteresis loop measurements show differences between Fe particular film with strong in-plane uniaxial anisotropy and Co one, which is almost isotropic in the plane of the film. Nanoparticular film thicknesses and volume fractions of particles were obtained using spectroscopic ellipsometer UVISEL. Ellipsometric data were fitted to the model based on the Bruggeman effective medium approximation.

Magnetic Domain Patterns in Bilayered Ribbons Studied by Magnetic Force Microscopy and Magneto-Optical Kerr Microscopy

The magnetic domain patterns of amorphous bilayered FeSiB/FeNbSiB and FeNbCuSiB/CoSiB ribbons are observed and analysed using the magneto-optical Kerr microscopy (MOKM) and magnetic force microscopy (MFM). Both microscopic techniques are highly sensitive to the sample surface; possibility of Kerr microscopy to visualize the domains separately in both layers is achieved by focusing the laser spot on the ribbon cross section. Wide curved domains as well as fine fingerprint domains were detected at the surface of ribbons due to presence of local stresses coming from the preparation process. With respect to high lateral resolution of MFM and its out-of-plane magnetization sensitivity, the perpendicularly magnetized crossed stripe domain patterns can be selected as well. Coiling of the ribbons on the half-round-end sample holder is often used to induce and control the magnetic anisotropy of these alloys. Changes in the magnetic domain structure at the outer-coiled surface and its dependence on the sign of magnetostriction coefficient are discussed in detail. Finally, the MFM images in the presence of external in-plane magnetic field up to ±40 kA/m are shown.

FeCoAlN films with induced magnetic anisotropy

Nowadays, an intensive research of new magnetic materials with high frequency permeability has been stimulated by the demand for electronic devices, such as microinductors, transformers and magnetic recording heads, operating in the GHz-frequency range [1]. Soft magnetic nanogranular films consisting of magnetic grains embedded in an insulating matrix are appropriate candidates for these applications due to: (a) the intrinsic maze structure of nanogranular films leads to high resistivity which reduces eddy current losses, (b) the ferromagnetic resonance (FMR) can be shifted to higher frequencies in materials with high saturation magnetization and high anisotropy field. Research on nanogranular ferromagnetic FeCoAlN films is presented.