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

The magnetization, polarization, and band-gap energy in pure and ion-doped ${\mathrm{KNbO}}_3$ (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 $E_g$ also depends on the dopants. $E_g$ 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

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

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

The mononuclear and dinuclear ruthenium(III) complexes trans-Ph₄P[Ru^III(acac)₂Cl₂] (1), Ph₄P[{Ru^III(acac)Cl}₂(μ-Cl)₃] (2) and trans-Ph₄P[Ru^III(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 (μ_eff) are 2.00 and 1.93 μ_B for 1 and 3·0.5C₆H₁₄, respectively, and 0.66 μ_B 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 Ru^III → Ru^IV redox wave at 0.23 V (vs. Fc/Fc⁺) for 1 and the Ru^III → Ru^II waves at −1.39 V for 1 and −1.25 V for 3·0.5C₆H₁₄ and the Ru^III–Ru^III → Ru^III–Ru^IV and Ru^III–Ru^III → Ru^III–Ru^IV waves at 0.91 V and −0.79 V for 2. Full article

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

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