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Magnetochemistry, Volume 10, Issue 3 (March 2024) – 6 articles

Cover Story (view full-size image): The LNCMI (France) aims at offering static magnetic fields up to 43 T (Grenoble) and non-destructive pulsed magnetic fields up to 100 T (Toulouse). A high electrical current must be injected into an appropriate resistive coil. Bulk materials (DC fields) and wires (pulsed fields) must exhibit a very high mechanical strength to withstand the stresses caused by the Lorentz forces induced via the generation of the magnetic field. Moreover, conductors that make up the resistive magnets must have an electrical resistivity as low as possible. The key to success is thus to add a very small silver content and tailor the conductor's appropriate micro/nano structuration by mastering the innovative successive process steps of powder metallurgy, cold-spray, and wire drawing. View this paper
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11 pages, 341 KiB  
Article
Doping Effects on the Multiferroic Properties of KNbO3 Nanoparticles
by A. T. Apostolov, I. N. Apostolova and J. M. Wesselinowa
Magnetochemistry 2024, 10(3), 19; https://doi.org/10.3390/magnetochemistry10030019 - 07 Mar 2024
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Abstract
The magnetization, polarization, and band-gap energy in pure and ion-doped KNbO3 (KNO) bulk and nanoparticles (NPs) are investigated theoretically using a microscopic model and Green’s function theory. It is shown that KNO NPs are multiferroic. The size dependence of M and P [...] Read more.
The magnetization, polarization, and band-gap energy in pure and ion-doped KNbO3 (KNO) bulk and nanoparticles (NPs) are investigated theoretically using a microscopic model and Green’s function theory. It is shown that KNO NPs are multiferroic. The size dependence of M and P is studied. The magnetization M increases with decreasing NP size, whereas the polarization P decreases slightly. The properties of KNO can be tuned by ion doping, for example, through the substitution of transition metal ions at the Nb site or Na ions at the K site. By ion doping, depending on the relation between the doping and host ion radii, different strains appear. They lead to changes in the exchange interaction constants, which are inversely proportional to the lattice parameters. So, we studied the macroscopic properties on a microscopic level. By doping with transition metal ions (Co, Mn, Cr) at the Nb site, M increases, whereas P decreases. Doped KNO NPs exhibit the same behavior as doped bulk KNO, but the values of the magnetization and polarization in KNO NPs are somewhat enhanced or reduced due to the size effects compared to the doped bulk KNO. In order to increase P, we substituted the K ions with Na ions. The polarization increases with increasing magnetic field, which is evidence of the multiferroic behavior of doped KNO bulk and NPs. The behavior of the band-gap energy Eg also depends on the dopants. Eg decreases with increasing Co, Mn, and Cr ion doping, whereas it increases with Zn doping. The results are compared with existing experimental data, showing good qualitative agreement. Full article
(This article belongs to the Special Issue Magnetic Materials, Thin Films and Nanostructures (Volume II))
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16 pages, 8751 KiB  
Article
The Influence of Current Magnitudes and Profiles on the Sedimentation of Magnetorheological Fluids: An Experimental Work
by Elliza Tri Maharani, Myeong-Won Seo, Jung Woo Sohn, Jong-Seok Oh and Seung-Bok Choi
Magnetochemistry 2024, 10(3), 18; https://doi.org/10.3390/magnetochemistry10030018 - 07 Mar 2024
Viewed by 870
Abstract
Magnetorheological fluids (MRFs) are widely used for various kinds of controllable devices since their properties can be controlled by an external magnetic field. Despite many benefits of MRFs, such as fast response time, the sedimentation arisen due to the density mismatch of the [...] Read more.
Magnetorheological fluids (MRFs) are widely used for various kinds of controllable devices since their properties can be controlled by an external magnetic field. Despite many benefits of MRFs, such as fast response time, the sedimentation arisen due to the density mismatch of the compositions between iron particles and carrier oil is still one of bottlenecks to be resolved. Many studies on the sedimentation problem of MR fluids have been carried out considering appropriate additives, nanoparticles, and several carrier oils with different densities. However, a study on the effect of current magnitudes and profiles on the sedimentation is considerably rare. Therefore, this study experimentally investigates sedimentation behaviors due to different current magnitudes and different magnitude profiles such as square and sine waves in different diameters. The evaluation was performed by visual observation to obtain the sedimentation rate. It was found that the average sedimentation rate of the square type of current is slower compared to the sinusoidal type. It has also been identified that the higher intensity of the applied current results in a stronger electromagnetic field, which could slow down the sedimentation. The results achieved in this work can be effectively used to reduce particle sedimentation in the controller design of various application systems utilizing MRFs in which the controller generates a different magnitude and different profile of the external magnetic field. Full article
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20 pages, 489 KiB  
Article
Advances in Engine Efficiency: Nanomaterials, Surface Engineering, and Quantum-Based Propulsion
by Mario J. Pinheiro
Magnetochemistry 2024, 10(3), 17; https://doi.org/10.3390/magnetochemistry10030017 - 27 Feb 2024
Viewed by 768
Abstract
This study explores ground-breaking methods for improving engine efficiency by combining cutting-edge materials, theoretical frameworks, and alternative energy paradigms. The paper primarily offers a cohesive framework, built from our variational method which combines thermal and entropic engines. We investigate the fabrication of hydrophobic [...] Read more.
This study explores ground-breaking methods for improving engine efficiency by combining cutting-edge materials, theoretical frameworks, and alternative energy paradigms. The paper primarily offers a cohesive framework, built from our variational method which combines thermal and entropic engines. We investigate the fabrication of hydrophobic and other functionally specific surfaces using nanomaterials and sophisticated surface engineering techniques that efficiently utilize entropy gradient forces. Additionally, this publication explores the fields of quantum-based propulsion systems and information-burning engines, creating a connecting link between theoretical foundations and real-world technical implementations. The study emphasizes the multifaceted character of engine research and its crucial role in shaping a future in which sustainability and efficiency are intimately connected. Full article
(This article belongs to the Section Applications of Magnetism and Magnetic Materials)
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16 pages, 4918 KiB  
Article
Syntheses, Structures, and Properties of Mono- and Dinuclear Acetylacetonato Ruthenium(III) Complexes with Chlorido or Thiocyanato Ligands
by Kai Nakashima, Chihiro Hayami, Shino Nakashima, Haruo Akashi, Masahiro Mikuriya and Makoto Handa
Magnetochemistry 2024, 10(3), 16; https://doi.org/10.3390/magnetochemistry10030016 - 27 Feb 2024
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Abstract
The mononuclear and dinuclear ruthenium(III) complexes trans-Ph4P[RuIII(acac)2Cl2] (1), Ph4P[{RuIII(acac)Cl}2(μ-Cl)3] (2) and trans-Ph4P[RuIII(acac)2(NCS)2 [...] Read more.
The mononuclear and dinuclear ruthenium(III) complexes trans-Ph4P[RuIII(acac)2Cl2] (1), Ph4P[{RuIII(acac)Cl}2(μ-Cl)3] (2) and trans-Ph4P[RuIII(acac)2(NCS)2]·0.5C6H14 (3·0.5C6H14) were synthesized. Single crystals of 1, 2·H2O and 3·CH3CN suitable for X-ray crystal structure analyses were obtained through recrystallization from DMF for 1 and 2·H2O and from acetonitrile for 3·CH3CN. An octahedral Ru with bis-chelate-acac ligands and axial chlorido or κ-N-thiocyanido ligands (for 1 and 3·CH3CN) and triply µ-chlorido-bridged dinuclear Ru2 for 2·H2O were confirmed through the structure analyses. The Ru–Ru distance of 2.6661(2) of 2·H2O is indicative of the existence of the direct metal–metal interaction. The room temperature magnetic moments (μeff) are 2.00 and 1.93 μB for 1 and 3·0.5C6H14, respectively, and 0.66 μB for 2. The temperature-dependent (2–300 K) magnetic susceptibility showed that the strong antiferromagnetic interaction (J ≤ −800 cm−1) is operative between the ruthenium(III) ions within the dinuclear core. In the 1H NMR spectra measured in CDCl3 at 298 K, the dinuclear complex 2 showed signals for the acac ligand protons at 2.50 and 2.39 ppm (for CH3) and 5.93 ppm (for CH), respectively, while 1 and 3·0.5C6H14 showed signals with large paramagnetic shifts; −17.59 ppm (for CH3) and −57.01 ppm (for CH) for 1 and −16.89 and −17.36 ppm (for CH3) and −53.67 and −55.53 ppm (for CH) for 3·0.5C6H14. Cyclic voltammograms in CH2Cl2 with an electrolyte of nBu4N(ClO4) showed the RuIII → RuIV redox wave at 0.23 V (vs. Fc/Fc+) for 1 and the RuIII → RuII waves at −1.39 V for 1 and −1.25 V for 3·0.5C6H14 and the RuIII–RuIII → RuIII–RuIV and RuIII–RuIII → RuIII–RuIV waves at 0.91 V and −0.79 V for 2. Full article
(This article belongs to the Section Molecular Magnetism)
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13 pages, 13711 KiB  
Article
High-Strength Copper/Silver Alloys Processed by Cold Spraying for DC and Pulsed High Magnetic Fields
by Simon Tardieu, Hanane Idrir, Christophe Verdy, Olivier Jay, Nelson Ferreira, François Debray, Anne Joulain, Christophe Tromas, Ludovic Thilly and Florence Lecouturier-Dupouy
Magnetochemistry 2024, 10(3), 15; https://doi.org/10.3390/magnetochemistry10030015 - 21 Feb 2024
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Abstract
High-strength, high-conductivity copper/silver-alloyed materials were prepared by cold-spray (CS) manufacturing. For DC high-field application at room temperature, bulk Cu/Ag (5% vol. Ag) alloys with high mechanical properties and high electrical conductivity can be obtained by CS and post-heat treatments. For pulsed-field application at [...] Read more.
High-strength, high-conductivity copper/silver-alloyed materials were prepared by cold-spray (CS) manufacturing. For DC high-field application at room temperature, bulk Cu/Ag (5% vol. Ag) alloys with high mechanical properties and high electrical conductivity can be obtained by CS and post-heat treatments. For pulsed-field application at liquid nitrogen temperature, bulk Cu/Ag (5% vol. Ag) alloys serve as precursors for room-temperature wire drawing. The Cu/Ag-alloyed bulk CS deposit presents a high yield strength of about 510 MPa with a corresponding electrical resistivity of 1.92 µΩ·cm (at 293 K). The Cu/Ag-alloyed wires show a very high ultimate tensile strength (1660 MPa at 77 K or 1370 MPa at 293 K) and low electrical resistivity (1.05 µΩ·cm at 77 K or 2.56 µΩ·cm at 293 K). Microstructural studies via STEM allow us to understand this very high level of mechanical strength. The results evidence that materials developed by CS exhibit very high mechanical properties compared to materials prepared by other routes, due to the high velocity of the deposited particles, which leads to high initial deformation rates and specific microstructural features. Full article
(This article belongs to the Special Issue Feature Papers in Materials for High Field Resistive Magnets)
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11 pages, 4377 KiB  
Article
Nano-Magnonic Crystals by Periodic Modulation of Magnetic Parameters
by Alison Roxburgh and Ezio Iacocca
Magnetochemistry 2024, 10(3), 14; https://doi.org/10.3390/magnetochemistry10030014 - 21 Feb 2024
Viewed by 929
Abstract
Magnonic crystals are metamaterials whose magnon behavior can be controlled for specific applications. To date, most magnonic crystals have relied on nanopatterning and magnetostatic waves. Here, we analytically and numerically investigate magnonic crystals defined by modulating magnetic parameters at the nanoscale, which predominantly [...] Read more.
Magnonic crystals are metamaterials whose magnon behavior can be controlled for specific applications. To date, most magnonic crystals have relied on nanopatterning and magnetostatic waves. Here, we analytically and numerically investigate magnonic crystals defined by modulating magnetic parameters at the nanoscale, which predominantly act on exchange-dominated, sub-100 nm magnons. We focus on two cases: the variation in the exchange constant, and the DMI constant. We found that the exchange constant modulation gives rise to modest band gaps in the forward volume wave and surface wave configurations. The modulation of the DMI constant was found to have little effect on the magnonic band structure, leading instead to a behavior expected for unpatterned thin films. We believe that our results will be interesting for future experimental investigations of nano-designed magnonic crystals and magnonic devices, where material parameters can be locally controlled, e.g., by thermal nano-lithography. Full article
(This article belongs to the Special Issue Spin Waves in Magnonic Crystals and Hybrid Ferromagnetic Structures)
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