Magnetochemistry, Volume 10, Issue 4 (April 2024) – 10 articles

Columnar phases consisting of a group of carbon toroidal molecules (C₁₂₀, C₁₉₂, C₂₅₂, C₂₈₈) are studied numerically. Each nanotorus was previously doped with an iron atom. This made it possible to use an external magnetic field as a tool for influencing both an individual molecule and a linear fragment of the columnar phase. A high-precision scheme for calculating the dynamics of large molecules with a rigid frame structure is proposed to solve the problem. The group dynamics of nanotori clusters under the influence of an external magnetic field has been studied using classical molecular dynamics methods. The influence of the molecular cluster size, temperature, magnetic moment of the molecule, and magnetic field direction on the collective behavior of iron-doped toroidal molecules with different contents of carbon atoms is analyzed. Molecular dynamics calculations showed that systems of nanotori doped with a single iron atom retain a columnar structure both in the absence and in the presence of an external magnetic field. The columnar fragment behaves as a stable linear association of molecules even at sufficiently high values of magnetic induction, performing a coordinated collective orbital rotation around a common center of mass on a nanosecond time scale. Full article

The manipulation of droplets plays a vital role in biomedicine, chemistry, and hydromechanics, especially in microfluidics. Magnetic droplet manipulation has emerged as a prominent and advanced technique in comparison to other modes such as dielectric infiltration, optical radiation, and surface acoustic waves. Its notable progress is attributed to several advantages, including excellent biocompatibility, remote and non-contact control, and instantaneous response. This review provides a comprehensive overview of recent developments in magnetic droplet manipulation and its applications within the biomedical field. Firstly, the discussion involves an examination of the distinctive features associated with droplet manipulation based on both permanent magnet and electromagnet principles, along with a thorough exploration of the influencing factors impacting magnetic droplet manipulation. Additionally, an in-depth review of magnetic actuation mechanisms and various droplet manipulation methods is presented. Furthermore, the article elucidates the biomedical applications of magnetic droplet manipulation, particularly its role in diagnostic assays, drug discovery, and cell culture. Finally, the highlights and challenges of magnetic droplet manipulation in biomedical applications are described in detail. Full article

The contributions of magnetohydrodynamic (MHD) vortexes to chiral electrodeposition in a vertical magnetic field were theoretically examined based on the three-generation model of the 2D nucleus, 3D nucleus, and screw dislocation; for the vortexes to rotate in the second and third-generation, the kinematic viscosity must be at least 10⁻¹⁸ and 10⁻³⁰ times lower than the ordinary value in the first generation, i.e., almost equal to zero. This implies that the ionic vacancy created on the electrode surface works as an atomic-scale lubricant. At the same time, the vortexes played three roles: promotion and suppression of nucleation, and transport of the chirality from the upper generation to the lower generation through precessional motion. Then, the rule of the chirality transfer was established, and finally, the relationship between the chiral activity and magnetic field was clarified in the presence and absence of chloride ions. Full article

Ni-MOF, as a metal–organic framework, has the advantages of morphological diversity and adjustable composition, which make its derivatives attractive for electromagnetic wave absorption. However, it is challenging for Ni-MOF derivatives to obtain strong absorption at low filling rates. Herein, ternary Ni@C/PPy composites based on Ni-MOF derivatives were synthesized by cooperatively coupling magnetic Ni@C nanoparticles with a conductive polymer PPy matrix through a facile self-assembly method. Among them, Ni@C nanoparticles are formed after Ni-MOF pyrolysis, and PPy serves as the backbone to effectively assemble and support the Ni@C nanoparticles. As a result, the Ni@C/PPy-3 sample exhibited excellent performance with a reflection loss value of −50.65 dB at a filling ratio of 15 wt% and a thickness of 2.5 mm. At the same time, its effective absorption bandwidth reached 6.24 GHz, covering the whole Ku frequency band. The results show that in comparison to pure Ni@C composite, the Ni@C/PPy multi-component composite with a porous structure shows significant advantages in terms of optimizing impedance matching, which can effectively enhance the interface polarization and, thus, greatly improve its electromagnetic absorption ability. In summary, this work provides a valuable research idea for developing strong absorbing properties of absorbing materials at a low filling rate. Full article

This study proposes the thermal decomposition of salt compounds and doping of carbonyl iron powders (CIPs) to optimize the preparation of an insulating layer through the solid-phase interface reaction. First, (Fe–Si–Cr + CIPs)/ZnSO₄ composite powders were synthesized using the hydrothermal method and (Fe–Si–Cr + CIPs)/ZnO·SiO₂·Cr₂O₃ SMCs with a ZnO·SiO₂·Cr₂O₃ composite insulation layer were prepared through heat treatment and cold pressing. The effect of the CIP doping content on the microstructure and magnetic properties of the (Fe–Si–Cr + CIPs)/ZnO·SiO₂·Cr₂O₃ SMCs were then investigated. During the heat treatment, ZnSO₄ decomposed into solid ZnO and gaseous SO₂ and O₂. The O₂ drives the solid-phase reaction, prompting the migration of nonmagnetic Si and Cr atoms from the interior of the Fe–Si–Cr soft magnetic powder to the surface insulation layer, finally forming the ZnO·SiO₂·Cr₂O₃ insulation layer. The doped CIPs also show good plasticity during the coating process, combining with the coating layer to fill the internal pores of SMCs. Moreover, as the particles are small with a high surface area, they increase the number of reaction sites for ZnSO₄ decomposition and facilitate the growth of the composite insulation layer, promoting its uniform distribution on the surfaces of the soft magnetic powders and CIPs. The lattice mismatch between the insulation layer and soft magnetic powder is reduced while the magnetic-phase content is increased, allowing the effective doping of CIPs sin the insulation layer. The magnetic properties of SMCs can be precisely regulated by changing the doping amount of CIPs. Unlike other insulating layer–preparation strategies based on the interfacial solid-phase reaction, the proposed method exploits the high plasticity and specific surface area of CIPs and removes the lattice mismatch between the insulation layer and soft magnetic powder. Full article

In this work, evidence of isothermal magnetic entropy change ($∆S_M$) over a broad temperature region is presented in a series of La_1.4Sr_1.6Mn_2−xNb_xO₇ Ruddlesden–Popper compounds with niobium modification (Nb) (0.0 ≤ x ≤ 0.15) at the manganese (Mn) site. The ceramic samples were obtained through a solid-state sintering method in optimized conditions. All compounds predominantly possessed Ruddlesden–Popper phase while a few additional reflections were resolved in Nb-doped compounds which indicates the separation of structural phases. These peaks are assigned to a separate layered perovskite and single perovskite with tetragonal symmetry and hexagonal symmetry, respectively. The microstructure of the pure sample reveals uniform grain morphology but in Nb-doped specimens chiefly three types of grains were found. It was assumed that the inter-connected large particles were of R-P phase which is dominant in both parent and x = 0.05 compounds, while the hexagonal and polygonal morphology of grains in higher concentrations of dopants directly corroborates with the symmetry of single perovskite and additional layered perovskite phases, respectively. The parent compound exhibits a single $∆S_M$ curve, whereas all Nb-substituted samples display bifurcated $∆S_M$ curves. This indicated two transition regions with multiple magnetic components, attributed to distinct structural phases. The highest ${∆S}_M$ values obtained for components corresponding to the R-P phase are 2.32 Jkg⁻¹k⁻¹, 0.75 Jkg⁻¹k⁻¹, 0.58 Jkg⁻¹k⁻¹ and 0.43 Jkg⁻¹k⁻¹ and for the second component located around room temperature are 0.0 Jkg⁻¹k⁻¹, 0.2 Jkg⁻¹k⁻¹, 0.28 Jkg⁻¹k⁻¹ and 0.35 Jkg⁻¹k⁻¹ for x = 0.0, 0.05, 0.10 and 0.15 compositions, respectively, at 2.5 T. Due to the collective participation of both components the $∆S_M$ was expanded through a broad temperature range upon Nb doping. Full article

This research unveils a versatile Halbach array magnetic device with promising biomedical applications, offering innovative solutions for targeted therapy and disease management in evolving biomedical engineering. This paper explores the potential of a novel Halbach array-based device for harnessing magneto-mechanical phenomena in biomedical applications. The study employs computational modeling using COMSOL Multiphysics to define the device’s magnetic properties and validate its operation within the theoretical prediction. The research catalogs the device’s operational modes and assesses crucial parameters related to magneto-mechanical biomedical modalities, including magnetic field strength, gradient, and force. Experimental validation of numerical findings through magnetic field measurements confirms the device’s multifaceted potential, particularly in targeted drug delivery and tissue engineering applications. Finally, the adaptability of the magnetic arrangements for various scenarios is also highlighted. This investigation provides valuable insights into integrating magneto-mechanical principles into biomedical engineering. It paves the way for further research and innovative approaches in theranostics, positioning the presented apparatus as a promising tool with untapped potential for future exploration and discovery in the evolving biomedical field. Full article

This study explores the synthesis and characterization of chitosan/gelatine films incorporating nickel ferrite (NiFe₂O₄) and cobalt ferrite (CoFe₂O₄) nanoparticles. The magnetic nanoparticles exhibit superparamagnetic behaviour, making them attractive for various applications, including biomedical uses. The X-ray diffraction analysis confirmed the successful synthesis of NiFe₂O₄ and CoFe₂O₄ nanoparticles, and the scanning electron micrographs illustrated well-dispersed ferrite nanoparticles within the biopolymer network, despite the formation of some aggregates attributed to magnetic interactions. Magnetization loops revealed lower saturation magnetization values for the composites, attributed to the chitosan/gelatine coating and the dielectric studies, indicating increased dielectric losses in the presence of ferrites, particularly pronounced in the case of NiFe₂O₄, suggesting interactions at the interface region between the polymer and ferrite particles. The AC conductivity shows almost linear frequency dependence, associated with proton polarization and conduction processes, more significant at higher temperatures for samples with ferrite particles. Full article