The aim of this work was to analyze the influence of resin content on contribution of the hysteresis, eddy current and anomalous losses to the total losses in the frequency range from DC to 150 kHz. The samples of composite material were prepared in the form of the ring with outer diameter of 25 mm, inner diameter of 17 mm and height approximately 3 mm and in the form of cylinder with diameter of 25 mm and height approximately 3 mm by a compaction of mixture of iron powder ASC100.29 (90 vol.%) and commercial termoset resins. The DC hysteresis losses were obtained by the measurements of DC hysteresis loops and the total power losses in the frequency range 0.4 Hz-150 kHz from AC hysteresis loops, both at maximum induction 0.05, 0.1 and 0.2 T. The magnetic properties of the composite rings were compared with the properties of the material prepared from the powder supported by Höganäs AB Sweden. By analyzing the frequency dependence of total losses of the Fe-based SMC we found out that hysteresis losses contribute to the total losses as a majority component.
In this work, two soft magnetic Fe_{73}Cu_{1}Nb_{3}Si_{16}B_{7} powder core samples were investigated. Samples were prepared by milling of amorphous Fe_{73}Cu_{1}Nb_{3}Si_{16}B_{7} ribbon at different temperature conditions: sample R, by milling at room temperature and sample L, by cryomilling at temperature of liquid nitrogen. Influence of applied exciting AC magnetic field with various amplitudes on the complex permeability spectra was studied. Obtained results are explained by the dynamics and relaxation phenomenon of domain walls under the influence of AC magnetic field.
The relations of core losses with the frequency of FeNiMo alloys were investigated. The core energy losses were determined by the measurements of dc and ac hysteresis loops as functions of frequency (1 Hz-50 Hz). The usual three-component concept of separation of core losses consisting of hysteresis, eddy current and anomalous losses was used to explain the influence of the powder particle size on core loss frequency dependences.
We have investigated the magnetic behavior of magnetite nanoparticles covered by the 11-mercaptoundecanoic acid around magnetite core prepared by a standard co-precipitation method. The particles show superparamagnetic behavior at room temperature, with transition to a blocked state at blocking temperature 91 K estimated from zero field cooled and field cooled at 500 Oe experiment. The hysteresis loop measured at 293 K showed magnetization 32.8 emu/g at 50 kOe without any coercivity. The mean particle size (7.1 nm) was determined by fitting a magnetization curve obtained at 295 K assuming a log-normal size distribution.
An analysis of several variants of the Fe/polymer/SiO₂ composites in terms of the impact of iron powder particle shape (irregular, spherical), of the content (0.4-2.0 wt%), of the polymer type (shellac, thermoset SL450) and the method of its application as well as the effect of the preparation procedure of the composites (mixing and/or vacuum-pressure impregnation) on properties of electrical insulating layer (thickness and coherence), electrical resistivity and magnetic properties was carried out. It was found that the main governing factor of the microstructure formation is the shape, surface microgeometry of the iron particles and the insulator layer. These determine not only the uniformity of thickness and cohesion of the insulating layer of the applied polymer or its hybrid modification (polymer+SiO₂ nanoparticles), but also the most suitable method of preparation in terms of the achieved values of electrical and magnetic properties of the composites.
We investigated coercivity, total losses and complex permeability of sintered Fe-Co powder cores to detect magnetization processes performing in ac magnetic field. The Fe-Co solid solution alloy powders with 50:50 wt% ratio were prepared by 1, 15, and 20 h alloyed mixture of pure chemical elements in planetary ball mill. The resulting powder was subsequently sintered into a disk form. The compaction was performed at a pressure of 800 MPa for 5 min at temperatures of 400°C, 500°C and 600°C in vacuum oxidation protective atmosphere, with pressure of 5×10¯³ Pa. The best magnetic properties exhibit sample prepared from 1 h alloyed powder, compacted at 600°C.
In this paper possibility of application two-dimensional vector Preisach model for bulk materials was investigated. Physical magnetization mechanisms in bulk cores and thin ribbons were analyzed. Model is based on collection of the Preisach planes which describe material state in different angles on rotation plane. Presented model exhibits good conformity with experimental data for bulk as well for ribbon shaped cores. Model includes anisotropy and describes not only mean magnetization vector, but also distribution of magnetic moments for different angles.
This paper highlights recent advances in synthesis and magnetotransport properties of magnetic Co nanoparticles. It is shown that magnetic Co nanoparticles self-assembled in nanoparticular monolayers revealing giant magnetoresistance similar to granular systems but with additional features resulting from dipolar interactions between small domains of nanoparticles. A spin-valve with one magnetic Co nanoparticular electrode is employed as a model to demonstrate that individual magnetic moments of Co nanoparticles can be coupled to a magnetic Co layer which in turn offers tailoring of the resulting giant magnetoresistance characteristics. In addition, it is demonstrated that combining a magnetic on-off ratchet with magnetic tunneling junctions integrated in the ratchet introduces a new biosensor concept enabling: (1) simultaneous transporting and separating biomolecules, (2) dynamical biomolecule detection when passing magnetic tunneling junctions in a 1D arrangement. It is projected that this biosensor concept could be applied for viruses as well as for bacteria.
The aim of this work was to investigate the influence of resin content on AC magnetic properties of Vitroperm 800-based composite material to extend possibilities for application of this kind of material at higher frequency (up to 100 kHz). The samples of composite material were prepared in the form of the ring with outer diameter of 25 mm, inner diameter of 18 mm and height approximately 3 mm. Powder mixtures were prepared from Vitroperm 800 in partial nanocrystalline state and commercial termoset resins by mechanical mixing. The AC magnetic properties (losses) at maximum induction up to 0.5 T were measured by MATS-2010SA loop tracer in frequency range 1-100 kHz. The specific resistivity of the material was measured by the van der Pauw method. The magnetic properties of the composite rings were compared with the properties of the material prepared from Fe based powder supported by Höganäs. It was found out that the total losses of the Vitroperm-based soft magnetic composite are more than 10 times lower (at 10 kHz) than that for Fe-based one.
The study presents magnetization process behaviour versus operating temperature up to 100°C in dual-phase ferromagnets in the light of their complex permeability spectra and energy losses from quasi-dc regime up to about 1 MHz upon defined peak induction. The samples consist of two Co- and Fe-based ball-milled-ribbon powders mixed in the same mass ratio. The magnetic characterization has been carried out by a digital hysteresisgraph-wattmeter using complex permeability approach to the linear material. Temperature invoked reduction of anisotropy leads to the decrease of hysteresis losses and significantly affects the low-frequency part of permeability and losses that is ascribed to domain wall movement. The high-frequency behaviour remains unchanged with respect to increase of temperature.
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