Elemír Ušák

Frequency dispersion of permeability in ferrite polymer composites

The permeability spectra of sintered MnZn ferrite and magnetopolymers prepared by mixing the ferrite particles with polymer have been studied. The experimental data have been compared with predictions of magnetic circuit model described for dynamic conditions. The applied model analyses the effect of the demagnetising field due to shape and size of ferrite particles.

Magnetic and Structural Properties of Nickel Zinc Ferrites Doped With Yttrium

The aim of this paper is to investigate the effect of Y³⁺ ions substitution for Fe³⁺ ions in Ni_0.42Zn_0.58Y_xFe_2-xO₄(x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) compounds, synthesized by means of ceramic technique, on the magnetic properties and magneto-chemical composition and structure. It was achieved by the X-ray spectroscopy, analysis of the behavior of susceptibility with changing temperature, magnetic hysteresis loop measurement, and complex permeability spectra.

Design of Magnetic Cloak for Experiments in AC Regime

The magnetic shielding device causing only negligible distortion of external magnetic field is called the magnetic cloak. We have designed and tested cloaks with a coaxial bilayer structure where a superconducting cylindrical layer is placed inside the tube from a ferromagnetic material. Such object when inserted in the bore of a coil generating ac magnetic field should not change the coils impedance. This experiment is suitable for checking the cloak performance in the ac regime by measuring the voltage on the coil terminations, particularly the change in its amplitude and phase. The impact on signal amplitude comes from the nonzero magnetic moments of the cloak components. Then, the opposite character of ferromagnetic and diamagnetic material can be used to suppress the response, e.g., by modifying the thickness of the ferromagnetic layer. On the other hand, the shift in the phase comes from the hysteresis behavior of both constituents, and their impacts are additive. We achieved decent results using the ferrite powder/epoxy composite for the outer tube and REBCO superconducting tapes for the inner cylinder. Numerical simulations and experimental verification were used to investigate the electromagnetic response at various geometrical arrangements of the superconducting part of the cloak.

Magnetic Properties Analysis of Rare-Earth Substituted Nickel Zinc Ferrites

The raw compounds with the chemical composition Ni_0.42Zn_0.58Me_xFe_2-xO₄ where Me = Eu, Gd, La (x = 0, 0.01, 0.02, 0.04, 0.06) were synthesized by means of the ceramic technique. The magnetic properties and magneto-chemical composition and structure of various doped nickel zinc ferrites were estimated by X-ray spectroscopy, EDAX analysis, and study of the behavior of susceptibility with changing temperature, complex permeability spectra, and magnetic hysteresis loop measurement.

Analysis of Selected Be-Substituted NiZn Ferrites

Polycrystalline NiZn ferrites with the chemical formula (Ni_0.3Zn_0.7)_1- <i>x</i>Be<i>x</i>Fe₂O ₄with Be substituent ion <i>x</i>=0, 0.05, 0.1, and 0.25 have been prepared by the ceramic method. The intrinsic and certain extrinsic magnetic properties such as the coercivity <i>H</i> _c, initial permeability ¿<i>i</i>and hysteresis loops of the ferrites have been measured and discussed from the point of view of the substituting element contents as well as the grain size. The MO¿ssbauer spectra of certain samples have been analysed as well. According to the requirement of specific applications the properties of NiZn, ferrite have to be improved by means of proper substitution of selected ions and processing technology.

A new approach to modeling of loss separation in grain-oriented Fe-Si laminations

A model of magnetic loss separation based on the distribution of relaxation times is suggested. If the magnetic flux excitation is sinusoidal and the magnetization process by planar 180° domain wall movement is dominant, then it is possible to separate the hysteretic and dynamic part of total losses analytically. The experimental verification of proposed model is performed on a set of grain-oriented laminations cut at various angles with respect to the rolling direction.

Comparision of simulated and measured magnetisation curves using a rigorously identified moving Preisach model

The consequent identification of the Preisach function requires a knowledge of the correct hypothetical field, allowing the transformation of measured first-order reversal curves from external to internal field dependencies. In the present paper we discuss the difficulties we met during the application of theoretically correct algorithm to soft magnetic materials with Preisach function concentrated near macroscopic coercivity and with relatively low non-congruency.

Effect of lanthanum substitution on structural and magnetic properties of nickel zinc ferrites

The purpose of the presented research is to investigate the effect of La3+ ions substitution for Fe3+ ions in Ni0.42Zn0.58LaxFe2-xO4 (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) ferrite compositions prepared by the innovated glycine-nitrate process based on auto-combustion method. Structural and magnetic properties of examined samples were estimated by the analysis of X-ray spectra, EDAX spectrum, SEM micrographs, thermomagnetic characteristics, magnetic hysteresis loops and complex permeability spectra.

Influence of iron substitution by selected rare-earth ions on the properties of NiZn ferrite fillers and PVC magneto-polymer composites

Nickel-zinc ferrites are very important soft magnetic materials from the point of view of diverse technical applications (such as, e.g., various electronic devices and components) for their high magnetic permeability and permittivity, low core loss, high resistivity, high Curie temperature as well as mechanical strength and chemical stability. Due to their good absorbing properties, they can be used as microwave absorbing and shielding materials with the aim of decreasing the environmental pollution caused by non-ionizing microwave radiation. The ferrite material incorporated into the polymer matrix creates qualitatively new magneto-polymer composite material taking benefits from both components. The properties typical for polymers (elasticity, mouldability, etc.) are combined with good high-frequency magnetic parameters, thus allowing to utilize these materials, e.g., in high-frequency applications where especially flexibility of composite materials plays a key role. Small amounts of selected rare-earth ...

Analysis of Microstructural Changes in Soft Magnetic Materials Based on Direct Evaluation of Magnetization Process Dynamics

A correlation between thermal aging and the dynamics of magnetization processes (especially domain wall motions) in standard steel sheet materials were studied. The response of magnetic quantities, e.g., the flux density and/or induced voltage, to artificial aging induced by annealing of the samples at 753 K for aging time ta ranging from 0 to 60 h was investigated. Ring-shaped samples were magnetized with defined exciting field having special waveform shape allowing direct observation of transients associated with sudden change of waveform attributes (e.g., slope). The parameters of observed first-order exponential-like transient curves were demonstrated to be influenced by heat treatment of the samples. Obtained results allow the application of suggested procedure as a promising new method for nondestructive inspection of various ferromagnetic construction materials.