Michal Lesňák

Physical properties of Al doped Ba hexagonal ferrite thin films

We developed the thin film microwave magnetic material, M-type barium hexagonal ferrite (BaM) doped with Al, for signal processing devices operating above 40 GHz with little to no applied magnetic field. Al was chosen as the dopant material because it significantly increases the already strong anisotropy field of BaM. A series of thin film BaAlxFe12-xO19 samples, x ranging from 0 to 2 in 0.25 steps, were deposited on Pt templates using a metal-organic decomposition growth technique. The resulting films are polycrystalline and highly textured, with the hexagonal c-axis directed out of plane. These films are also self-biasing; easy axis hysteresis loops have a high squareness ratio, s, in the 0.83-0.92 range. As expected, the anisotropy field increases with x, ranging from 1.34 to 2.19 × 106 A/m (16.9-27.5 kOe) for x = 0-2, while the saturation magnetization Ms decreases with x, ranging from 0.334 to 0.175 × 106 A/m (4πMs = 4.2-2.2 kG) for x = 0-2. These values were measured at room temperature, but the tem...

The effect of FeF2 on the magneto-optic response in FeF2/Fe/FeF2 sandwiches

The room temperature optical constants n and k of MBE grown FeF2 films are reported. Because of poor chemical stability, FeF2 had to be coated with a protective Au layer. Reflection spectral ellipsometry in the photon energy range between 1.3 and 5.2 eV was performed on structures with a typical profile Au(0.5 nm)/FeF2(120 nm)/Au(30 nm)/Ag(20 nm)/Fe(0.6 nm) grown on GaAs(0 0 1) substrate. The spectra of n and k in FeF2 were subsequently employed in the design of FeF2/Fe/FeF2 sandwiches considered as magneto-optic (MO) sensors for weak microwave currents. Their MO response was evaluated using reflection MO (Kerr) spectroscopy at polar magnetization. The present results may be of interest in MO studies of magnetic nanostructures with Fe/FeF2/Fe, including MO magnetometry and MO magnetic domain imaging.

Magnetic defectoscope with permanent magnets

The paper is intended for the theory of magnetic defectoscope of steel ropes, construction of this equipment and evaluation of measured data. The detector module consists of magnetization head, sensing system and holder with optoelectronic rotary increment encoder. The wavelet transform — a new and promising method for defectoscope signal processing — is presented. It enables to specify the changes of the rope cross-section with an accuracy level better than 0.5%.

Designing of MO-SPR bio-chip with photonic crystal

The magneto-plasmonic response in planar multilayer with prism coupling composed from Fe and Au bilayer supplied by photonic crystal (Ta2O5 / SiO2) is studied. Modeled structure is intended as a sensor unit combining magneto-optical (MO) and surface-plasmon-resonance (SPR) effects. The sensitivity of MO-SPR system by small variations of analyte refractive index is tested to obtain optimal resolution ability.

Magneto-plasmonic response as a perspective tool to magnetic field sensing

The non-reciprocity of magneto-optical reflection response by surface plasmon excitation in the planar Au/Fe/Au/glass nano-systems with prism coupling is studied. These structures are intended as magnetic field sensor units combining magneto-optical (MO) and surface-plasmon-resonance (SPR) effects. The ability of MO-SPR systems to magnetic field sensing is analysed using incidence-angle-depending response function (Rpp (+) – Rpp (-))/(Rpp (+) + Rpp (-)), where Rpp denotes the reflectance of p-polarized beam; and, the sign in upper index relates to the orientation of external magnetic field. The proposed sensitivity criteria F and K (the magnitude and inflexed tangent of the response function oscillation) are applied in transverse MO configuration. Mathematical model based on the own matrix algorithm is applied to simulate the diffraction response to varying external magnetic field at the wavelength 632.8 nm. Obtained theoretical results are compared with experiments realized using the measuring device Multiskop (Optrel GbR, Germany).

Effective medium approximation of anisotropic materials with radiative correction

A measurable magneto-optical activity of nanoparticles made out of noble metals is observed when the localized plasmon waves are excited in the presence of external magnetic field. We confirmed these observations for quite general Au nanostructure on SiO2/Si substrate theoretically and by experimental way. The heterogeneous layer is formed as a field of cylindrical or spheroidal nanodots of various size having the same height and parallel symmetry axis. These properties enable to apply the Bruggeman’s model of effective medium approximation, for which the size of dots (height, diameter) and fill-factor of nanodots were specified using the transmission electron microscopy image processing. Actually, this model is extended about the interaction of magnetic dipole moments simulated using discrete dipole approximation via geometrical averaging. Derived computational algorithm leads to better agreement with experimental data in the form of Kerr angles in polar configuration at visible spectral region. Obtained out-puts also illustrate the fact that extinction peak of plasmon excitation is located at the resonance wavelength of permittivity.

Surface plasmon structures with ferromagnetic thin films

The paper is devoted to Au/Fe/Au/glass and Au/Fe/glass structures intended as MO SPR sensor units. The model approach based on matrix algebra is used to describe the response of discussed structures to external magnetic field. The theoretical results are confirmed by experiments realized by Multiscope device. The attention has been focused on a sensitivity of proposed response factors ρ±(Φ) and F to magneto-optical effects. The application of ρ±(Φ) response factor for our structures description is limited. The F factor has practically linear character such as change of external magnetic field and ferromagnetic thin film thickness.

Magnetic Field Distribution Around Magnetized Steel Ropes and Its Modulation by Rope Defects

The paper is devoted to the modelling of the magnetic field around magnetized steel rope kinds using the ANSYS software package. The influence of wire cracks on the amplitude distribution of the generated field is specified for two steel rope kinds assuming surface and inner defects. The first rope is characterized by six rope strands where each is completed by 28 wires (two different diameters, 11 thick wires and 15 thin ones), while the second one has a Z-geometry with special cross section of wires located on rope surface. The results show a significant influence of surface defects (more 10 mT) and measurable magnetic flux responses (in the frame some mT) by cracks in the inner wires with 1 mm gaps. The limits for nondestructive testing of demonstrated ropes are described in detail.

Homogeneous Magnetic Field Source For Attenuated Total Reflection

Abstract The paper is focused on the study of two-dimensional magnetic field distribution used for an analysis of samples containing magnetically active films by means of the Attenuated Total Reflection (ATR) method. The design of a proposed electromagnet and the magnetic field model computation are presented together with the results obtained from magnetic field distribution measurement. The ATR method can provide information about a thin film thickness, refractive index, and attenuation in addition to the perfunctory coupling of an optical wave into and off a waveguide [1, 2]. The prism coupling conditions are determined for magnetic structures with induced anisotropy. The prism - a film coupler is located in the central cavity of a magnetic yoke. By current switching in the coils, we can change the amplitude and magnetic field direction in order to modulate the induced anisotropy in a thin film with magnetic ordering. By the in-plane modulation of the magnetization direction in the samples, we can change the rotation and elasticity of outgoing light.

Study of Steel Wire Ropes Defects

This article deals with the study of defects in steel wire. In the study we model magnetic fields around rope genetated by magnetized part of rope. The work is based on the finite element program ANSYS. For the purposes of the experiments we consider one strand wire rope construction. We define different kinds of defects and faults. The shape of the magnetic induction lines of generated fields depends on the size of the defect, the depth of rope violation or the presence of other nearby defects. The location and number of disturbances have been chosen to achieve the most versatile outputs. All of these modifications were analyzed and the results displayed in the 3D colored.