Magnetochemistry, Volume 8, Issue 8 (August 2022) – 19 articles

Two mononuclear Ru^III complexes of formula trans-[RuCl₄(Hgua)(dmso)]·2H₂O (1) and trans-[RuCl₄(Hgua)(gua)]·3H₂O (2) [Hgua = protonated guanine (gua), dmso = dimethyl sulfoxide] have been synthesized and characterized magnetostructurally. 1 and 2 crystallize in the monoclinic system with space groups P2₁/n and Pc, respectively. Each Ru^III ion in 1 and 2 is bonded to four chloride ions and one (1) or two (2) nitrogen atoms from guanine molecules and one sulfur atom (1) of a dmso solvent molecule, generating axially compressed octahedral geometries in both cases. In their crystal packing, the Ru^III complexes are connected through an extended network of N-H⋯Cl hydrogen bonds and π⋯Cl intermolecular interactions, forming novel supramolecular structures of this paramagnetic 4d ion. Variable-temperature dc magnetic susceptibility data were obtained from polycrystalline samples of 1 and 2 and their plots show a different magnetic behavior. While 1 is a ferromagnetic compound at low temperature, 2 exhibits a behavior of magnetically isolated mononuclear Ru^III complexes with S = 1/2. The study on ac magnetic susceptibility data reveal slow relaxation of the magnetization, when external dc fields are applied, only for 2. These results highlight the presence of field-induced single-ion magnet (SIM) behavior for this mononuclear guanine-based Ru^III complex. Full article

We discuss the problem of electron transfer (ET) in mixed valence (MV) molecules that is at the core of molecular Quantum Cellular Automata (QCA) functioning. Theoretical modelling of tetrameric bi-electronic MV molecular square (prototype of basic QCA cell) is reported. The model involves interelectronic Coulomb repulsion, vibronic coupling and ET between the neighboring redox sites. Unlike the majority of previous studies in which molecular QCA have been analyzed only for particular case when the Coulomb repulsion energy significantly exceeds the ET energy, here we do not imply assumptions on the relative strength of these two interactions. Moreover, in the present work we go beyond the adiabatic semiclassical approximation often used in theoretical analysis of such systems in spite of the fact that this approximation ignores such an important phenomenon as quantum tunneling. By analyzing the electronic density distributions in the cells and the ell-cell response functions obtained from a quantum-mechanical solution of a complex multimode vibronic problem we have concluded that such key features of QCA cell as bistability and switchability can be achieved even under failure of the condition of strong Coulomb repulsion provided that the vibronic coupling is strong enough. We also show that the semiclassical description of the cell-cell response functions loses its accuracy in the region of strong non-linearity, while the quantum-mechanical approach provides correct results for this critically important region. Full article

In this work, we present magnetic nanoparticles based on iron oxide doped with zinc synthesized using the wet co-precipitation method for environmental application. The morphology of the samples was revealed by SEM and TEM, which showed particles of granular shape and size of about 15 nm. The specific surface areas of the materials using the BET method were within the range of 85.7 to 101.5 m² g⁻¹ depending on the zinc content in the superparamagnetic iron oxide nanoparticles (SPIONs). Magnetometry was performed to determine the magnetic properties of the particles, indicating superparamagnetism. Synthesized magnetic nanoparticles with different amounts of zinc dopant were used as an adsorbent to remove model pollutant Titan yellow (TY) from the aqueous solutions. Adsorption was determined by investigating the effects of sorbent amount, dye concentration, and contact time. The synthesized material removed Titan yellow quickly and efficiently within the physical adsorption. The adsorption isotherms were consistent with the models proposed by Langmuir and Redlich-Peterson. The monolayer adsorption capacities were 30 and 43 mg g⁻¹ for Fe₃O₄ and Fe₃O₄@10%Zn, respectively, for the removal of TY. However, that of Congo red is 59 mg g⁻¹ by Fe₃O₄@10%Zn. The proposed nanoparticles offer fast and cost-effective water purification, and they can be separated from solution using magnets. Full article

In this work, we report on the fabrication of nanocomposites based on superparamagnetic iron oxide nanoparticles (SPIONs) in combination with hydroxyapatite (HAp) as a platform for drug delivery and magnetic hyperthermia application. First, the influence of experimental conditions such as co-precipitant, bath temperature, and pH on the morphology and magnetic properties of SPIONs was investigated. Then, the superparamagnetic particles were coated with the hydroxyapatite layer for further loading of anticancer drugs, determining the optimal thickness of the HAp shell. The composite was fabricated by the wet chemical process and was characterized by optimizing the experimental conditions of the wiring synthesis to obtain the superparamagnetic spherical material with a high HAp loading as a platform for drug uptake. SEM and TEM studies confirmed the round shape of the magnetic core up to 15 nm in size with a well-defined HAp shell. After checking the material’s superparamagnetic properties, the temperature dependence on time and alternating magnetic field strength was tested and optimized in hyperthermia experiments. Full article

CrSBr is a stable two-dimensional (2D) van der Waals (vdW) magnet with intralayer ferromagnetic and interlayer antiferromagnetic couplings. Here, we propose to use CrSBr as the barrier in spin-filter (sf) MTJ and establish the devices based on graphene/CrSBr/graphene structures. Employing density functional theory (DFT) combined with the nonequilibrium Green’s function approach, we investigated the transmission details, and the results show TMR values above 330%, 2 × 10⁷% and 10⁵% with two-, four- and six-layer CrSBr at zero bias, respectively. Subsequently, we systematically analyze the transmission spectra, transmission eigenstates, electrostatic potentials, band structures and local density of states to elaborate the underlying mechanism of the TMR effect in the sf-MTJs. Our results indicate the great prospect of CrSBr-based sf-MTJs in applications, and provide guidance for futural experiments. Full article

We studied the thermal features of magnetized plasmas in the Martian subsolar magnetosheath using MAVEN’s observations from 2014 to 2019. Statistical analyses show that the average ion and electron temperature in the Martian subsolar magnetosheath are 210 and 31 eV, respectively, which are significantly lower than their counterparts in the subsolar magnetosheaths of Earth and Saturn which both have an inherent magnetosphere. However, the ratio ${\overline{T}}_i/{\overline{T}}_e$ in the Martian subsolar magnetosheath is about 6.8, which is very close to that of Earth and Saturn. We further investigated the relationship between $T_i/T_e$ and the bulk ion flow velocity $V_i$, as well as the relationship between the total plasma beta $\beta$ and $V_i$. Results show that the average value of $T_i/T_e$ when $V_i<300\mathrm{km}/\mathrm{s}$ is considerably higher than when $V_i>300\mathrm{km}/\mathrm{s}$. A value of $V_i$ closer to 250–300 km/s leads to a higher average value of the total plasma beta $\beta$. These results confirm the prediction of previous researchers, that there is not enough room for solar wind thermalization as the distance between the Martian bow shock and the so-called obstacle is of the order of a solar wind proton gyroradius. Full article

In this work, we have studied the elastocaloric effect in directionally solidified Co_51.6V_31.4Ga₁₇ alloys with a strong [001] preferred orientation. The entropy change for thermal-induced martensitic transformation is determined as 19.6 J kg⁻¹ K⁻¹. The sample exhibits stress-induced martensitic transformation with a hysteresis of 46 MPa, and the superelasticity is also verified by the in situ X-ray diffraction method. According to the elastocaloric effect tests, a noticeable change in adiabatic temperature up to 12.2 K has been achieved at the strain of 6%. The specific temperature change upon the critical stress loading can be attained as 132 K MPa⁻¹. In addition, the difference in the loading–unloading temperature change can be ascribed to the imperfect adiabatic environment. Full article

We present the new synthesis root of spinel-structure FeCr₂O₄ and its single crystal growth by the optical floating zone method, ensuring its single phase and near-ideal composition. The advantage of the proposed synthesis method is the creation of the reducing atmosphere in the oven needed for preserving the Fe²⁺ oxidation state via decomposition of the iron (II) oxalate FeC₂O₄ used as one of the initial components. The occurrence of the Fe³⁺ ions in the obtained polycrystalline samples as well as grown single crystals was carefully monitored by means of Mössbauer spectroscopy. Magnetic susceptibility and heat capacity temperature dependences reveal a sequence of the structural (138 K) and magnetic (at 65 K and 38 K) phase transition characteristics for the FeCr₂O₄ compound. Full article

Magnetic Fe₃O₄ nanoparticles (MNPs) have great potential for nucleic acid separation, detection, and delivery. MNPs are considered a valuable tool in biomedicine due to their cost-effectiveness, stability, easy surface functionalization, and the possibility of the manipulations under a magnetic field. Herein, the synthesis of magnetic nylon 6 nanocomposites (MNPs@Ny6) was investigated. Transmission electron microscopy (TEM) was used for morphology and size analysis. A new method of UV-induced immobilization of oligonucleotides on MNPs@Ny6 for nucleic acid magnetic separation was proposed. MNPs@Ny6 shows a high oligonucleotide binding capacity of 2.2 nmol/mg with 73.3% loading efficiency. The proposed system has been applied to analyze model mixtures of target RNA on the total yeast RNA background. The RNA target isolation efficiency was 60% with high specificity. The bind RNA release was 88.8% in a quantity of 0.16 nmol/mg. The total RNA capture efficiency was 53%. Considering this, the MNPs@Ny6 is an attractive candidate for nucleic acids-specific magnetic isolation. Full article

This work details the construction and optimization of a fully automated, custom-built, remote controlled vibrating sample magnetometer for use in spintronics related research and teaching. Following calibration by a standard 6 mm diameter Ni disc sample with known magnetic moment, hysteresis measurements of Nd-Fe-B thin films acquired by this built vibrating sample magnetometer were compared to the data taken using a commercial superconducting quantum interference device and showed very similar results. In plane and out of plane magnetic hysteresis data acquired for 25 nm Fe thin films are also presented. The developed vibrating sample magnetometer is able to achieve a sensitivity approaching 1 × 10⁻⁵ emu. Further alterations to the design that may improve beyond this limit are also discussed. Full article

Iron oxide magnetic nanoparticles (MNPs) have been widely studied due to their versatility for diagnosis, tracking (magnetic resonance imaging (MRI)) and therapeutic (magnetic hyperthermia and drug delivery) applications. In this work, iron oxide MNPs with different single-core (8–40 nm) and multi-core (140–200 nm) structures were synthesized and functionalized by organic and inorganic coating materials, highlighting their ability as magnetic nanotools to boost cell biotechnological procedures. Single core Fe₃O₄@PDA, Fe₃O₄@SiO₂-FITC-SiO₂ and Fe₃O₄@SiO₂-RITC-SiO₂ MNPs were functionalized with fluorescent components with emission at different wavelengths, 424 nm (polydopamine), 515 (fluorescein) and 583 nm (rhodamine), and their ability as transfection and imaging agents was explored with HeLa cells. Moreover, different multi-core iron oxide MNPs (Fe₃O₄@CS, Fe₃O₄@SiO₂ and Fe₃O₄@Citrate) coated with organic (citrate and chitosan, CS) and inorganic (silica, SiO₂) shells were tested as efficient nanoheaters for magnetic hyperthermia applications for mild thermal heating procedures as an alternative to simple structures based on single-core MNPs. This work highlights the multiple abilities offered by the synergy of the use of external magnetic fields applied on MNPs and their application in different biomedical approaches. Full article

Pulsed laser-deposited (PLD) MnBi films were fabricated by alternating deposition of Mn and Bi layers. In order to obtain the ferromagnetic MnBi phase, heat treatments were performed on the samples. Simultaneously, the resistance of the samples was monitored as a function of the temperature. Thus, on increasing the temperature, a steep decrease in the resistance of the films was observed, simultaneous to the onset of the formation of the MnBi phase. At room-temperature, these annealed samples showed a ferromagnetic behavior, as well as the presence of the characteristic LT-MnBi phase diffraction peaks in the X-ray diffraction patterns. The temperature of the generation of the MnBi phase depended on the relative concentration of Mn and Bi in the different samples: on increasing the Bi atomic concentration, the temperature of the generation of the MnBi phase decreased. Full article

The concept of charge transfer (CT) transitions in ferrites is based on the cluster approach and takes into account the relevant interactions, such as the low-symmetry crystal field, spin–orbital, Zeeman, exchange and exchange-relativistic interactions. For all its simplicity, this concept yields a reliable qualitative and quantitative microscopic explanation of spectral, concentration, temperature and field dependencies of optic and magneto-optic properties ranging from the isotropic absorption and optical anisotropy to circular magneto-optics. In this review paper, starting with a critical analysis of the fundamental shortcomings of the “first-principles” density functional theory (DFT-based) band theory, we present the main ideas and techniques of the cluster theory of the CT transitions to be main contributors to circular magneto-optics of ferrites. Numerous examples of comparison of cluster theory with experimental data for orthoferrites, iron garnets and other ferrites are given. Full article

The downstream processing of natural active molecules remains the most significant cost in the production pipeline. This considerable cost is largely attributed to rigorous chromatographic purification protocols. In an ongoing effort to abate the dependence on chromatography in downstream processing, alternative affinity matrices in the form of magnetic particles (e.g., iron oxide) have emerged as viable candidates. Nevertheless, biotechnological applications of iron oxide particles are still confined to the research level or for low-throughput clinical applications. Herein, we describe an efficient, quick, and environmentally friendly method for the isolation of astaxanthin and lutein, two carotenoids with very similar chemical structure, from extracts of the microalga Haematococcus pluvialis. The technology proposed, named Selective Magnetic Separation (SMS), is based on the use of magnetic materials carrying affinity ligands that bind carotenoids and is applied as second step of purification. The method, thanks to functionalized magnetic nanoparticles, reduces the use of organic or toxic solvents. In the present work, we examined the most efficient binding conditions such as temperature, magnetic nanoparticles concentration, and elution time, as well as their effects on carotenoids recovery, with the aim to improve the non-covalent binding between the ligand (amines) and astaxanthin/lutein. Our initial results clearly showed that it is possible to use magnetic separation as an alternative to chromatography to isolate important and valuable compounds. Full article

Magnetite nanoparticles and clusters of nanoparticles have been of Increasing scientific interest in the past decades. In order to prepare nanoparticles and clusters that are stable in suspension, different coatings have been used. Phosphates and phosphonates are a preferred anchoring group for the coating of magnetite nanomaterials. However, poly(vinylphosphonates) have rarely been used as a coating agent for any nanoparticles. Here, poly(methylvinylphosphonate) and other substituted polyvinylphosphonates are described as new coatings for magnetite nanoparticles and clusters. They show great stability in aqueous suspension. This is also the first time phosphonate-coated magnetite clusters have been synthesized in a one-pot polyol reaction. The coated magnetite nanoparticles and clusters have been characterized by TEM, EDX, FTIR, magnetization measurement, XRD as well as XPS. It has been shown that substituted vinylphosphonates can be easily synthesized in one-step procedures and as a polymeric coating can imbue important properties such as stability in suspension, tight binding to the particle surface, the ability to be further functionalized or to tightly adsorb metal ions. For the synthesis of magnetite clusters the cluster formation, polymerization and coating are done in a one-pot reaction and the resulting magnetite clusters show a higher amount of phosphonate coating than with a three-step procedure including a ligand exchange. Full article

In this article, based on the theory of micromagnetism, a microstructural model of the behavior of the Heusler alloy in a magnetic field is constructed. The dynamics of the magnetic process is described by the Landau–Lifshitz–Gilbert equation. Using the Galerkin procedure, variational equations corresponding to the differential relations of the magnetic problem are written out. For numerical simulation, we consider the problem of magnetization of a Ni${}_2$MnGa alloy polytwin crystals, each grain of which is a twinned variant of martensite and has pronounced anisotropic properties. First, we consider the process of magnetization of a single grain, when an external magnetic field is applied at different angles to the anisotropy axes of twinned variants, and then, based on the results obtained, we plot magnetization curves for various (isotropic and texture-oriented) polycrystalline samples. This paper does not consider the process of detwinning, which can occur in such a material during the magnetization at a sufficiently high external field strength. Full article

The detailed Raman scattering investigation of the lattice and spin dynamics of a single crystal of the $\mathrm{F}{\mathrm{e}}_3\mathrm{B}{\mathrm{O}}_6$ antiferromagnet is reported. Azimuthally resolved polarization measurements provided an unambiguous determination of the symmetry of observed excitations. Low-temperature experiments at $T=4.2$ K allowed us to reduce anharmonic contribution and deconvolute several overlapping phonon modes. Low-frequency measurements have made it possible to find two excitations at 13.1 and 16.6 cm${}^{-1}$, which were assigned to quasi-ferromagnetic and quasi-antiferromagnetic magnon excitations, respectively. The magnetic field applied along the hard-magnetization axis causes energy shifts of these excitations, but no spin-flip transition was observed up to $B=30$ T. Full article

We consider magnetic resonance force microscopy (MRFM) in the situation when the frequency of the electron spin resonance matches the fundamental frequency of the cantilever with a ferromagnetic particle attached to its tip. We suggest that in this situation, the quantum states of the oscillating cantilever may represent a qubit. We develop a scheme for manipulation with the qubit state and derive the expression describing the Rabi oscillations of the qubit. Full article

The solid-state reaction method is used to synthesize W-type Sr hexagonal ferrites Sr_0.8Pr_0.2(Zn_1.0−xCo_x)₂Fe₁₆O₂₇ (x = 0.00, 0.15, 0.30, 0.45, 0.60, 0.75). The results of XRD for the W-type hexagonal ferrites, when Co content (x) is 0.00 ≤ x ≤ 0.75, exhibit that they are in the single W-type hexaferrite phase. As shown by morphological analysis, the particles are hexagonal-shaped platelets. The saturation magnetization (M_s) and magneton number (n_B) increases with Co content (x) from 0.00 to 0.60. M_s and n_B begins to decrease at Co content (x) ≥ 0.60. With increasing Co content (x) from 0.00 to 0.75, the magnetic anisotropy field (H_a), first anisotropy constant (K₁), and coercivity (H_c) decrease gradually. The values of DC electrical resistivity for W-type hexagonal ferrites Sr_0.8Pr_0.2(Zn_1.0−xCo_x)₂Fe₁₆O₂₇ (0.00 ≤ x ≤ 0.75) are in the range of 20.854 × 10⁷ Ω-cm and 22.755 × 10⁷ Ω-cm. Full article