arXiv subjects

Alexander S. Sokolov

Publications and source records attributed to Alexander S. Sokolov.

4 recordsLinked to original sources

arXiv2019

High Performance Metallic Amorphous Magnetic Flake-based Magnetodielectric Inductors

Flake-shaped FeSi-based metallic amorphous alloy particles, having an aspect ratio as high as 175 to 1, were prepared by ball milling gas atomized amorphous powders of an effective diameter of 20 micrometers. The starting powder had a saturation magnetic flux density, Bs, of 1.5 T and a coercivity, Hc, of 94 A/m. The aspect ratio of the flakes, as well as their magnetic properties, were controlled by milling process parameters, such as duration, speed, and the type, mass and diameter of the milling balls. To minimize the oxidation of the charge, the powders were handled in an argon gas-purged glove box, milled in toluene, and subsequently dried in vacuo. Subsequently, soft magnetodielectric composites were prepared by suspending and aligning the FeSi-based powders in paraffin wax or epoxy resin. The composites were then pressed into toroids for measurements of their high frequency complex permeability by a vector network analyzer. The influence of the flake aspect ratio and volume loading fraction on the permeability of the composites were investigated. Results indicate that the composite permeability increases with the flake aspect ratio. For example, for a given loading factor of 30 vol.%, the composite permeability at 0.1 GHz nearly tripled and approached the value of 10 by increasing the aspect ratio of the FeSi-based inclusions from 1 (spheres) to greater than 175 to 1 (flakes).

physics.app-ph↗

arXiv2019

Stoichiometry, Phase, and Texture Evolution in PLD-Grown Hexagonal Barium Ferrite Films as a Function of Laser Process Parameters

Barium hexaferrite (BaFe12O19 or BaM) films were grown on c-plane sapphire (0001) substrates by pulsed laser deposition (PLD) to evaluate the effects of the laser fluence on their composition, structure, and magnetic properties. Continuum's Surelite pulsed 266nm Nd:YAG laser was employed, and the laser fluence varied systemically between 1 and 5.7 [J/cm2]. Deviations from the stoichiometric transfer between the BaM targets and deposited thin films occurred as the laser fluence changed. The Fe to Ba ratio in the films increased with the laser fluence. The films deposited at the laser fluences below 4 J/cm2 showed undesirable 3-dimensional islands on the surface. Moreover, insufficient laser energy resulted in the deposition of some secondary phases, for example, barium monoferrite (BaFe2O4) and Magnetite (Fe3O4). On the other hand, laser fluences above 5 J/cm2 promoted resputtering and degraded the film quality, structure, and magnetic properties. BaM films deposited at 4.8 J/cm2 - the optimal laser fluence - showed excellent c-axis orientation perpendicular to the film plane with the anisotropy field of 16 kOe and saturation magnetization of 4.39 kOe. These results clearly demonstrate a strong influence of the laser parameters on the PLD-grown hexaferrite films and pave the path for the high-yield production using PLD systems.

physics.app-ph↗

arXiv2018

3D Crystallographic Alignment of Alumina Ceramics by Application of Low Magnetic Fields

Non-cubic crystals exhibit anisotropic physical and functional properties. Microscopic crystallites as constituents of polycrystalline materials are randomly oriented, thus polycrystalline ceramics lack the anisotropic properties of their monocrystalline counterparts. We propose a technology that exploits the synergy between magnetic alignment and colloidal ceramics processing, and enables to independently tune the orientation of grains in different sample regions by infinitesimal magnetic fields (<10 millitesla). The grain pivot mechanism enables the emulation of single crystals, as well as the creation of large complex-shaped ceramic elements with designed crystallographic landscapes and spatially and directionally tuned properties. Ultra-high magnetic response arises from magnetic shape anisotropy of platelet-shaped seed crystallites coated with small amounts of iron oxide nanoparticles. To control crystallographic growth directions during subsequent annealing procedures, the seeds are dispersed and aligned in a matrix of chemically identical, but much finer spherical particles. The degree of crystalline orientation in accordingly prepared aluminum oxide exceeds 99%. This technology opens an avenue to remarkably improve structural and functional properties of ceramic elements employed in numerous industrial applications.

physics.app-ph↗

arXiv2018

Excellent microwave and magnetic properties of La-Cu substituted Ba-hexaferrites prepared by ceramic process

We demonstrate exceptional microwave magnetic performance of crystallographycally textured barium hexaferrites prepared by conventional ceramic method. Vibrating sample magnetometer (VSM) and rectangular cavity perturbation measurements indicate that bulk Ba0.8La0.2Fe11.2Cu0.2O19 samples exhibit a strong magnetic anisotropy field Ha of 14.6kOe, the highest remanent magnetization of 3.96kGs, and the lowest ferromagnetic resonance (FMR) linewidth of 401Oe with zero applied bias field at Q-band. Broadband millimeter-wave transmittance measurements determined the complex permeability and permittivity. The remanent magnetization, anisotropy field Ha, and effective linewidth were also estimated based on Schlomann's theory of the complex permeability. These calculated values are in good agreement with the VSM and FMR measurements.

physics.app-ph↗