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Magnetism, Volume 2, Issue 4 (December 2022) – 6 articles

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16 pages, 723 KiB  
Article
Simulation of a Hybrid Thermoelectric-Magnetocaloric Refrigerator with a Magnetocaloric Material Having a First-Order Transition
by Elías Palacios, Jesús Francisco Beltrán and Ramón Burriel
Magnetism 2022, 2(4), 392-407; https://doi.org/10.3390/magnetism2040028 - 12 Dec 2022
Viewed by 1572
Abstract
A simple hybrid thermoelectric-magnetocaloric (TE-MC) system is analytically and numerically simulated using the working parameters of commercial Peltier cells and the properties of a material with a first-order and low-hysteresis magneto-structural phase transition as La(Fe,Mn,Si)13H1.65. The need for a [...] Read more.
A simple hybrid thermoelectric-magnetocaloric (TE-MC) system is analytically and numerically simulated using the working parameters of commercial Peltier cells and the properties of a material with a first-order and low-hysteresis magneto-structural phase transition as La(Fe,Mn,Si)13H1.65. The need for a new master equation of the heat diffusion is introduced to deal with these materials. The equation is solved by the Crank–Nicolson finite difference method. The results are compared with those corresponding to a pure TE system and a pure MC system with ideal thermal diodes. The MC material acts as a heat “elevator” to adapt its temperature to the cold or hot source making the TE system very efficient. The efficiency of the realistic hybrid system is improved by at least 30% over the pure Peltier system for the same current supply and is similar to the pure MC with ideal diodes for the same cooling power. Full article
(This article belongs to the Special Issue Magnetocaloric Effect: Theory and Experiment in Concert)
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12 pages, 1822 KiB  
Article
Quasi-Stable, Non-Magnetic, Toroidal Fluid Droplets in a Ferrofluid with Annular Magnetic Field
by Alastair Radcliffe
Magnetism 2022, 2(4), 380-391; https://doi.org/10.3390/magnetism2040027 - 08 Dec 2022
Cited by 1 | Viewed by 1318
Abstract
A relatively stable, non-magnetic, torus-shaped fluid droplet within a linearly magnetizable surrounding ferrofluid medium, and subject to the annular magnetic field induced by an electric current in a wire passing perpendicularly through its centre, has been found through the use of coupled finite [...] Read more.
A relatively stable, non-magnetic, torus-shaped fluid droplet within a linearly magnetizable surrounding ferrofluid medium, and subject to the annular magnetic field induced by an electric current in a wire passing perpendicularly through its centre, has been found through the use of coupled finite element/boundary element computer simulations. Full article
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12 pages, 4333 KiB  
Article
Monopole Antenna Miniaturization with Magneto-Dielectric Material Loading Combined with Metal Parasitic Element
by Thomas Finet, Ala Sharaiha, Anne-Claude Tarot, Philippe Pouliguen, Patrick Potier and Cyrille Le Meins
Magnetism 2022, 2(4), 368-379; https://doi.org/10.3390/magnetism2040026 - 10 Nov 2022
Cited by 1 | Viewed by 1575
Abstract
In this paper is shown a new way to use Magneto-Dielectric Materials (MDM) in order to miniaturize monopole antennas. It is proposed to load an antenna with MDM to use the relative permeability to achieve the first 17% miniaturization rate. Then, in order [...] Read more.
In this paper is shown a new way to use Magneto-Dielectric Materials (MDM) in order to miniaturize monopole antennas. It is proposed to load an antenna with MDM to use the relative permeability to achieve the first 17% miniaturization rate. Then, in order to achieve better miniaturization, it is proposed to add metal parasitic plates on both sides of the material to use the relative permittivity to ensure capacitance useful to shift the antenna’s resonant frequency. By combining material loading, metallic plates’ capacitances and matching circuit designed with the real frequency technic, an antenna’s frequency shift from 350 MHz to 200 MHz is achieved corresponding to 43% of height reduction. A matching circuit has been designed to match the antenna at −5 dB. The obtained frequency bandwidth is 15% (185–215 MHz) with a realized gain of over −2.5 dBi. Full article
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12 pages, 4897 KiB  
Article
New Framework to Study Electromagnetic Turbulence
by Mario J. Pinheiro
Magnetism 2022, 2(4), 356-367; https://doi.org/10.3390/magnetism2040025 - 26 Oct 2022
Viewed by 1454
Abstract
Combining a current source involving vortical surface currents in the set of Maxwell’s equations offers a functional framework to address the complex phenomena of electromagnetic turbulence. The field structure equations exhibit fluid behavior with associated electromagnetic viscosity and reveal that the electromagnetic field, [...] Read more.
Combining a current source involving vortical surface currents in the set of Maxwell’s equations offers a functional framework to address the complex phenomena of electromagnetic turbulence. The field structure equations exhibit fluid behavior with associated electromagnetic viscosity and reveal that the electromagnetic field, as a fluid, shows turbulent properties. This is an entirely new mechanism, investigated for the first time to the best of our knowledge. The fluidic–electromagnetic analogy implies that diffraction is the analog phenomenon of EM turbulence. The method clarifies the role of vortical surface currents in generating electromagnetic turbulence and classical fractal-like behavior in optical devices and suggests norms to design suitable plasmon circuity to control electromagnetic turbulence in stealth technology and propulsion machines. Full article
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16 pages, 581 KiB  
Article
Low-Frequency Dynamic Magnetic Susceptibility of Antiferromagnetic Nanoparticles with Superparamagnetic Properties
by Igor S. Poperechny and Yuriy L. Raikher
Magnetism 2022, 2(4), 340-355; https://doi.org/10.3390/magnetism2040024 - 10 Oct 2022
Cited by 1 | Viewed by 1509
Abstract
As is known, the multi-sublattice structure of antiferromagnets (AFMs) entails that, under size diminution to the nanoscale, compensation of the sublattice magnetizations becomes incomplete. Due to that, the nanoparticles acquire small, but finite permanent magnetic moments. An AC field applied to such particles [...] Read more.
As is known, the multi-sublattice structure of antiferromagnets (AFMs) entails that, under size diminution to the nanoscale, compensation of the sublattice magnetizations becomes incomplete. Due to that, the nanoparticles acquire small, but finite permanent magnetic moments. An AC field applied to such particles induces their magnetic response, the measurement of which is well within the sensitivity range of the experimental technique. Given the small size of the particles, their magnetodynamics is strongly affected by thermal fluctuations, so that their response bears a considerable superparamagnetic contribution. This specific feature is well-known, but usually is accounted for at the estimation accuracy level. Herein, a kinetic model is proposed to account for the magnetic relaxation of AFM nanoparticles, i.e., the processes that take place in the frequency domain well below the magnetic resonance band. Assuming that the particles possess uniaxial magnetic anisotropy, the expressions for the principal components of the both linear static and dynamic susceptibilities are derived, yielding simple analytical expressions, including those for the case of a random distribution of the particle axes. Full article
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12 pages, 2548 KiB  
Article
Mössbauer Synchrotron and X-ray Studies of Ultrathin YFeO3 Films
by Marina Andreeva, Roman Baulin, Aleksandr Nosov, Igor Gribov, Vladimir Izyurov, Oleg Kondratev, Ilia Subbotin and Elkhan Pashaev
Magnetism 2022, 2(4), 328-339; https://doi.org/10.3390/magnetism2040023 - 29 Sep 2022
Cited by 3 | Viewed by 1526
Abstract
The YFeO3 orthoferrite is one of the most promising materials for antiferromagnetic (AFM) spintronics. Most studies have dealt with bulk samples, while the thin YFeO3 films possess unusual and variable properties. Ultrathin (3–50 nm) YFeO3 films have been prepared by [...] Read more.
The YFeO3 orthoferrite is one of the most promising materials for antiferromagnetic (AFM) spintronics. Most studies have dealt with bulk samples, while the thin YFeO3 films possess unusual and variable properties. Ultrathin (3–50 nm) YFeO3 films have been prepared by magnetron sputtering on the r-plane (1 1¯ 0 2)-oriented Al2O3 substrates (r-Al2O3). Their characterization was undertaken by the Mössbauer reflectivity method using a Synchrotron Mössbauer Source and by X-ray diffraction (XRD) including grazing incidence diffraction (GI-XRD). For thin films with different thicknesses, the spin reorientation was detected under the application of the magnetic field of up to 3.5 T. Structural investigations revealed a predominant orthorhombic highly textured YFeO3 phase with (00l) orientation for relatively thick (>10 nm) films. Some inclusions of the Y3Fe5O12 garnet (YIG) phase as well as a small amount of the hexagonal YFeO3 phase were detected in the Mössbauer reflectivity spectra and by XRD. Full article
(This article belongs to the Special Issue Magnetic Low-Dimensional Structures and Hybrid Materials)
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