Magnetochemistry, Volume 8, Issue 12 (December 2022) – 29 articles

In this study, impacts of using a sinusoidal shape encapsulated phase change material (PCM) packed bed (PB) system on the phase change and thermal performance are analyzed in multi-port vented cavity under a partially active magnetic field during hybrid nanoliquid convection. The current study is performed for different magnetic field strengths of domains (Hartmann number between 0 and 50), wave number (between 1 and 8), wave amplitude (between 0.01 H and 0.15 H), and nanoparticle loading (between 0 and 2%) by using the finite element method. The sinusoidal shape of the PCM-PB zone and varying its geometrical form are both found to affect the phase change process and thermal performance. When wave amplitude (Hp) rises from 0.01 H to 0.15 H, full phase change time (t-fr) increases by about 33% while average Nu increases by about 55%. When a partially active magnetic field is imposed at the highest value, up to 30.3% reduction in t-fr is obtained, while average Nu rises by about 9% at t = 18 min. The value of t-fr is reduced by about 15% while spatial average Nu rises by about 55% at the highest nanoparticle loading. Full article

This review is devoted to an analysis of currently known heterometallic molecular magnets based on an orbitally degenerate 5d metalloligand, [Re^IV(CN)₇]³⁻. Heptacyanidometallates with a pentagonal bipyramidal structure of the coordination site and degenerate ground spin state are the source of anisotropic magnetic exchange interactions upon the formation of cyanide-bonded assemblies involving the paramagnetic complexes of the first transition series. Therefore, the development of methods for chemical design using such molecular magnetic modules is extremely important. If for the 4d congener, isoelectronic [Mo^III(CN)₇]³⁻, a family of approximately 40 heterometallic compounds, was obtained, whereas for heptacyanorhenate(IV), no more than 20 are known. However, as a result of recent studies, heterobimetallic magnetic assemblies of all dimensionalities have been synthesized, from 0D to 1D, demonstrating slow magnetization relaxation, to 2D networks and 3D frameworks possessing large magnetic hysteresis. The most anisotropic is a 2D network, PPN[{Mn^III(acacen)}₂Re^IV(CN)₇]·Solv, with a critical temperature of 20 K and magnetic hysteresis with a record coercivity for cyanide-bridged molecular materials. Full article

The utilization of hybrid nanofluids (HNs) to boost heat transfer is a promising area of study, and thus, numerous scientists, researchers, and academics have voiced their admiration and interest in this area. One of the main functions of nanofluids is their dynamic role in cooling small electrical devices such as microchips and associated gadgets. The major goal of this study is to perform an analysis of the buoyancy flow of a shrinking/stretching sheet, whilst considering the fascinating and practical uses of hybrid nanofluids. The influence of a nonlinear heat source/sink induced by a micropolar fluid is also inspected. Water-based alumina and copper nanoparticles are utilized to calculate the fine points of the fluid flow and the features of heat transfer. The governing equations are framed with acceptable assumptions and the required similarity transformations are used to turn the set of partial differential equations into ordinary differential equations. The bvp4c technique is used to solve the simplified equations. Dual solutions are presented for certain values of stretching/shrinking parameters as well as the mixed convective parameter. In addition, the shear stress coefficient in the first-branch solution (FBS) escalates and decelerates for the second-branch solution (SBS) with the superior impact of the magnetic parameter, the mass transpiration parameter, and the solid nanoparticles volume fraction, while the contrary behavior is seen in both (FB and SB) solutions for the larger values of the material parameter. Full article

The complexity of Earth’s structure poses a challenge to the multiscale detection capability of geophysics. In this paper, we present a new wavelet-based three-dimensional inversion method for geomagnetic depth sounding. This method is based on wavelet functions to transfer model parameters in the space domain into the wavelet domain. The model is represented by wavelet coefficients containing both large- and fine-scale information, enabling wavelet-based inversion to describe multiscale anomalies. L₁-norm measurement is applied to measure the model roughness to accomplish the sparsity constraint in the wavelet domain. Meanwhile, a staggered-grid finite difference method in a spherical coordinate system is used to calculate the forward responses, and the limited-memory quasi-Newton method is applied to seek the solution of the inversion objective function. Inversion tests of synthetic data for multiscale models show that wavelet-based inversion is stable and has multiresolution. Although higher-order wavelets can lead to finer results, our tests present that a db6 wavelet is suitable for geomagnetic depth sounding inversion. The db6 inversion results of responses at 129 geomagnetic observatories around the world reveal a higher-resolution image of the mantle. Full article

The current research is focused on the chemical process and characterization of Co-based Y-type hexaferrite, electrochemically active polypyrrole doped with dodecylbenzene sulphonicacid (PPy-DBSA) and their composites. The microemulsion technique was used to produce hexaferrite with the formula Sr₂Co₂Fe₁₂O₂₂. The resistivity of pure ferrite specimens was 103 ohm-cm, which was lower than the 106 ohm-cm resistivity of the monomer utilized in the polymerization operation. As the temperature increases, the DC resistance decreases, revealing the specimens’ semiconductor nature. The cole-cole plots have been used to assess whether significant grain boundaries were involved in the dielectric relaxation process. By increasing the frequency, the electrochemical performance of all specimens was enhanced. Using the rate equation, ionic conductivity demonstrates that polarons are responsible for conduction. Because of the characteristics of the polymer PPY-conducting DBSA, the composites PPY/DBSA + Sr₂Co₂Fe₁₂O₂₂ exhibit a higher dielectric loss of 35 at 1 MHz. This specimen is perfect for electrical radiation shielding (EMI).These ferrites are widely used as permanent magnets, in microwave devices, high-density perpendicular media, and rigid disk media without lubricant and protective layers. Full article

Magnetite–gold dumbbell nanoparticles are essential for biomedical applications due to the presence of two surfaces with different chemical natures and the potential combination of magnetic and plasmonic properties. Here, the remote actuation of Fe₃O₄-Au hybrid particles in a rotating (1 Hz, 7 mT), static (7 mT) or pulsed low-frequency (31 Hz, 175 mT, 30 s pulse/30 s pause) magnetic field was studied. The particles were synthesized by a high-temperature wet chemistry protocol and exhibited superparamagnetic properties with the saturation magnetization of 67.9 ± 3.0 Am² kg⁻¹. We showcased the nanoparticles’ controlled aggregation in chains (rotating/static magnetic field) in an aqueous solution and their disaggregation when the field was removed. The investigation of nanoparticle uptake by LNCaP and PC-3 cancer cells demonstrated that Fe₃O₄-Au hybrids mainly escaped endosomes and accumulated in the cytoplasm. A significant fraction of them still responded to a rotating magnetic field, forming short chains. The particles were not toxic to cells at concentrations up to 210 μg (Fe₃O₄) mL⁻¹. However, cell viability decrease after incubation with the nanoparticles (≥70 μg mL⁻¹) and exposure to a pulsed low-frequency magnetic field was found. We ascribe this effect to mechanically induced cell destruction. Overall, this makes Fe₃O₄-Au nanostructures promising candidates for intracellular actuation for future magneto-mechanical cancer therapies. Full article

Electroless nickel plating with a nanofinished surface is used in space mirrors, automobile parts, aircraft components, optical instruments, and electronic equipment. Finishing of these components using conventional finishing techniques is limited due to size, shape, material, and process constraints. This work reports the nanofinishing of electroless nickel-plated surfaces using a magnetorheological finishing process where the surfaces are pre-treated with chemicals. The chemicals used in this work are hydrogen peroxide (H₂O₂) and hydrofluoric acid (HF). The effect of exposure time and concentration on the microhardness and roughness is studied to understand the surface chemistry after chemical treatment. The hydrogen peroxide forms a passivated layer, and it helps in easy material removal. Hydrofluoric acid improves surface quality and also helps in the removal of contaminants. The finished surface is characterized to understand the effect of chemical treatment on the finishing rate and surface topography. Normal and tangential forces are mainly affected by the hardness and surface condition after the chemical treatment. The best combination of parameters (chemical treatment with 1% HF for 30 min) was obtained and finishing was carried out to obtain a nanofinished surface with its areal surface roughness (Sa) reduced to 10 nm. Full article

Biomass is a material that can be potentially used as a natural fiber resource. Rice husk (RH) and sugarcane bagasse (SB), respectively containing 36.6% and 60% cellulose, are fibers that have the potential for biocomposite formation. In this study, an amine magnetic biocomposite (B-MNH₂) was prepared by a one-step solvothermal reaction. Delignified RH and SB fibers at a ratio of 1:1 were added to a mixture of ethylene glycol, iron chloride, and 1,6-hexanediamine, and kept in a stainless steel autoclave reactor at 200 °C for 6 h. The obtained B-MNH₂ contained 64.5% of Fe and 2.63 mmol/g of amine. Its surface area increased significantly from 9.11 m²/g to 25.81 m²/g after amine functionalization, and its optimum adsorption for Pb(II) ions was achieved within 360 min at 596.82 mg/g and pH 5. Moreover, the pseudo-first-order mechanism fitted well to the adsorption model. Other parameters, such as chemical oxygen demand (COD), total suspended solid (TSS), and dye during adsorption were also reduced by about 67.7%, 95.6%, and 89%, respectively. B-MNH₂ showed a slight decrease in performance by only 8% after the fourth repeated use. The amine magnetic biocomposite led to the development of a potential adsorbent due to the high surface area, stable material, and easy separation, and was capable of absorbing contaminants from an aqueous solution. Full article

An innovative magnetostatic force sensor consisting of a laser source, a tiny cantilever beam, and a small permanent magnet was developed and used for defect inspection in ferromagnetic samples in the present article. The penetrating zone within a ferromagnetic material under the magnetic field provided by a permanent magnet was called the magnetic sensing zone (MSZ), and surface or internal defects within the MSZ were inspected by measuring the change in the magnetostatic force. This magnetostatic force could be calculated by the Maxwell tensor integrating over the surface and interface of a ferromagnetic material. Numerical and experimental results demonstrated that this sensor was reliable and could precisely inspect the defects of different sizes in ferromagnetic samples. In summary, the sensor proposed in this paper has the potential for industrial applications to detect surface and sub-surface tiny defects on ferromagnetic steel thin sheets, such as the zinc slag defect of hot galvanized sheets, cracks on cold-rolled sheets, and the ferromagnetic oscillation marks of continuous casting. Full article

New tools for cancer diagnosis are being studied since early diagnosis can be crucial for a successful treatment. In this context, the use of NMR probes constitutes an efficient method of diagnosis. In this study, we investigated the use of ciprofloxacin to indirectly label the overexpression of topoisomerase-II enzymes by changes in ¹⁹F NMR chemical shifts of ciprofloxacin. Increased topoisomerase-II expression has been associated with cancer occurrence, mainly with aggressive forms of breast cancer, thus constituting a promising molecular target for new tumor cell identifiers. Using DFT calculations, we performed a spectroscopy analysis of ciprofloxacin in different chemical environments and evaluated the solvent and enzymatic effects. Our results show that ciprofloxacin forms a stable complex with the enzyme, and the main intermolecular interactions between ciprofloxacin and human topoisomerase-IIβ are hydrogen bonds, followed by π-π stacking and electrostatic interactions. Additionally, a shift of 6.04 ppm occurs in the ¹⁹F NMR signal when ciprofloxacin interacts with the human topoisomerase-IIβ enzyme, and this parameter may be an indirect marker indicating the overexpression of these enzymes in the body. Full article

Magnetic structure of functional magnetic dielectrics is traditionally of high interest. Here, we use the magnetic force microscopy (MFM) and nonlinear-optical probe of second harmonic generation for studies of surface domain structure of monocrystalline $L{u}_{2.1}B{i}_{0.9}F{e}_5{O}_{12}$ garnet films. The transformation of the magnetic domains under the application of the dc magnetic field is revealed by the MFM for both the top-view and the cleavage of the iron-garnet layer. Complementary magnetic force and second harmonic generation microscopy show that the considered film reveals the magnetization inclined with respect to the film’s normal, with its orientation being inhomogeneous within the film’s thickness. The second harmonic generation (SHG) microscopy confirms the zigzag structure of the surface-closing domain with the magnetization containing in-plane and out-of-plane magnetization components. We believe that these features of magnetic behavior of garnet films are important for the design of garnet-based magnetic devices. Full article

Heusler alloy with an atomic composition of Ni_51.82Mn_32.37In_15.81 was prepared by melt spinning from arc-melted ingots. X-ray diffraction, scanning electron microscopy and magnetic measurements were used to study the structural, microstructural and magnetic properties. The crystal structure consists of a mixture of $B2$ austenite (~50%) and $14M$ martensite (~50%). The alloy undergoes a second order magnetic transition at a Curie temperature of $T_c^A=194.2$K. The hysteresis loop reveals the occurrence of exchange bias phenomenon at room temperature. The critical exponents $\beta$, $\gamma$ and $\delta$ were estimated using modified Arrott plots, Kouvel–Fisher curves and critical isothermal analysis. The respective values are $\beta =0.500\pm 0.015$, $\gamma =1.282\pm 0.055$ and $\delta =3.003\pm 0.002$. The critical behaviour in ribbons is governed by the mean field model with a dominated long-range order of ferromagnetic interactions. The maximum entropy change, $∆S_M^{max}$, for an applied magnetic field of 5 T reaches an absolute value of 0.92 J/kg·K. The experimental results of entropy changes are in good agreement with those calculated using Landau theory. Full article

The sparking discharge process utilises high voltage to melt and evaporate tips of electrodes to create particles that can be deposited on substrate. In our research, we examine the influence of a magnetic field and nitrogen flow on gold thin-film formation onto quartz substrate. A positive effect of nitrogen flow and a 0.3 T external magnetic field was observed, in enhancement of surface plasmon band in UV visible and dispersal of nanoparticles without agglomeration. We also detected and described nitrification occurrences of gold measured by XPS at 407 eV and nitridification of quartz substrate on which gold particles are collected. These nitrogen-based chemical reactions occurred during sparking of gold wire inside of ambient air and in the magnetic field, as well during pure nitrogen flow. We measured the valence band electronic structure of gold nanoparticles deposited onto quartz substrate and found that gold thin film prepared in the magnetic field under nitrogen flow has the lowest value of 1.5 eV. Preparation of gold thin films in the magnetic field under nitrogen flow offers a highly dispersed and convenient method for productions of thin films. Full article

A novel magnetic catalyst with hollow cylinder shape based on K₂CO₃/γ-Al₂O₃/Sepiolite/CoFe₂O₄ was prepared to convert macroalgae oil (Fucus vesiculosus) into biodiesel in an unconventional reactor assisted by magnetic field. Catalysts were formulated by the extrusion and characterized satisfactorily by physicochemical (mechanical strength, XRD, TG/DTG, FTIR and TPD-CO₂), magnetic (VSM and EPR), morphological (SEM) and textural properties (BET). While their catalytic performance was also evaluated at 70 °C, oil: ethanol molar ratio 1:12 and 6 wt.% of catalyst using two different reaction systems for comparative purposes: (a) conventional stirred reactor and (b) fluidized bed reactor assisted by a magnetic field. The attained biodiesel presents properties in accordance with the standard limits (ASTM and EN) and total conversion (>99%) was observed in both cases after 2 h of reaction without significant differences between the two reactors. However, the magnetic properties of these catalysts allowed stabilization of the bed under a magnetic field and easy magnetic catalyst separation/recovery at the reaction end, showing their great potential for biodiesel production with regard to conventional process and thus, transforming it into a more sustainable technology. Full article

In this paper, 3 µm length and 200 nm diameter CoPt nanowire arrays (NWs) with different Co contents were prepared by electrodeposition at a controlled potential from an aqueous hexachloroplatinate solution. The synthesis occurred at two different solution pH values (2.5 and 5.5) in an electrochemical bath free of additives, as well as with saccharin as an organic additive. A complete morphological, compositional, structural and magnetic characterization of the as-prepared nanowires has been carried out. The results show that, by controlling the electrodeposition conditions, the Co content of the alloy can be tuned from 16% to 92%. The crystalline structure of the as-deposited compounds can also be controlled, with the obtained data showing that the face-centered cubic (fcc) crystalline structure changes into a hexagonal close-packed (hcp) structure when saccharin is used as an organic additive during the electrodeposition. The changes in the alloy’s composition and crystalline structure strongly influence the magnetic properties of the NW’s arrays. Full article

In this paper, (Tb_0.7Lu_0.3)₂O₃ magneto-optical transparent ceramics with different ZrO₂ doping levels (0~5 at%) were prepared by hydrogen sintering and sequential HIP technique using ZrO₂ as a sintering aid. The effect of ZrO₂ doping content on the microstructure and optical properties of (Tb_0.7Lu_0.3)₂O₃ ceramics was analyzed. We found that the optimal doping content of ZrO₂ was 3 at%. The transmittance of 3 at% ZrO₂-doped (Tb_0.7Lu_0.3)₂O₃ ceramics at the wavelength of 1064 nm was 74.84 %, and the Verdet constant was approximately 275.28 rad·T⁻¹·m⁻¹ at the wavelength of 650 nm. Full article

The green, cost-effective and sustainable synthesis of nanomaterials has been a key concern of scientists and researchers. In this view, MNPs were prepared using a sapota plant leaf extract and the surface of the magnetite nanoparticles was engineered with unsaturated fatty acids. The first report on the effect of unsaturation on the size and magnetic properties of magnetite nanoparticles (MNPs), prepared by the co-precipitation method, has been studied by coating surfactants on MNPs based on their unsaturation from zero to three (lauric acid, oleic acid, linoleic acid, linolenic acid). The size effect and magnetic properties of MNPs coated with a surfactant have been studied in comparison with uncoated magnetite nanoparticles. After the surface modification of the magnetite particle, it is necessary to check whether the magnetic property has been restored or not. Therefore, the magnetic property was studied. The presence of a surfactant on the surface of MNPs was confirmed by Fourier-transform infrared spectroscopy (FTIR), which was later confirmed by scanning electron microscope (SEM) and thermogravimetric analysis (TGA). The atomic structure was studied by X-ray diffraction (XRD) and the size of uncoated and surfactant-coated MNPs was determined by transmission electron microscopy (TEM) and the Scherrer equation by following XRD data. The magnetization property was analyzed by a vibrating sample magnetometer (VSM) at 10, 100 and 300 K and both bared and surfactant-coated MNPs exhibited a superparamagnetic nature at room temperature. The saturation magnetization (M_s) study shows that MNPs coated with a surfactant have a lower saturation magnetization value in comparison to uncoated NPs, confirming surface layering. Because the magnetic fluid has been stabilized in the aqueous medium, the double-layer model is expected to prevail. Full article

From the various aspects of spintronics the review highlights the area devoted to the creation of new functional materials based on magnetic semiconductors and demonstrates both the main physical phenomena involved and the technical possibilities of creating various devices: maser, p-n diode with colossal magnetoresistance, spin valve, magnetic lens, optical modulators, spin wave amplifier, etc. Particular attention is paid to promising research directions such as ultrafast spin transport and THz spectroscopy of magnetic semiconductors. Special care has been taken to include a brief theoretical background and experimental results for the new spintronics approach employing magnetostrictive semiconductors—strain-magnetooptics. Finally, it presents top-down approaches for magnetic semiconductors. The mechano-physical methods of obtaining and features of the physical properties of high-density nanoceramics based on complex magnetic oxides are considered. The potential possibility of using these nanoceramics as an absorber of solar energy, as well as in modulators of electromagnetic radiation, is shown. Full article

The recently intensified research in atomically thick two-dimensional (2D) materials has been motivated by their unique properties and the possibility of updating the future electronic and optoelectronic technologies. Doping can change the band structure of a semiconductor and regulate its physical and chemical properties. Doping has a significant effect on the electronic structure of 2D materials due to their atomic thickness. Here, we present a tutorial review of 2D doped materials (except graphene), including various doping types and theoretical calculations, the preparation and characterization methods, and its multifunctional application. Finally, we will summarize by stating the current challenges and future opportunities in the development of 2D doped materials. Full article

An amorphous carbon film with embedded detonation nanodiamond (DND) particles (a-C:ND) was produced by magnetron sputtering of nanodiamond powder. An Ag film was deposited on the carbon structure by radiofrequency magnetron sputtering. The silver film was irradiated with a 150 eV Ar⁺ to form plasmonic-active nanoparticles (NP) on the surface of the a-C:ND. The structure of the obtained a-C:ND and a-C:ND/Ag structures were studied by scanning and transmission electron microscopy, electron energy-loss spectroscopy, UV–Visible absorption spectroscopy, Raman spectroscopy, and fluorescence lifetime imaging at two-photon excitation. The analysis revealed 76% of sp³-carbon and a good dispersion of diamond nanoparticles in the a-C. Surface-enhanced Raman scattering (SERS) was applied to investigate the a-C:ND/Ag structure, allowing for the observation of SERS from the sp²-carbon species and the absence of significant a-C:ND damage after Ar⁺ irradiation of the Ag overlayer. A plasmonic-metal-enhanced luminescence was observed at one- and two-photon excitations, revealing a two- to five-fold intensity increase. The activity of the used DNDs was tested using the agar diffusion method and observed against the bacteria of Bacillus subtilis, Staphylococcus aureus, and Escherichia coli and the fungi of Aspergillus niger, Aspergillus fumigatus, and the yeast of Candida albicans, showing DND activity against all the test strains of fungi. Full article

With their outstanding mechanical and magnetic characteristics, two-dimensional magnetic materials have attracted wide attentions in the field of nanoelectromechanics and spintronics. By tuning the mechanical resonance with external knobs, such as strain, electric and magnetic control, nanoelectromechanical sensors with novel functionalities have been successfully demonstrated. Here, we investigate the mechanical properties of the suspended membranes with few-layered antiferromagnetic material CrOCl. The results show that the Young’s modulus of CrOCl resonators is ~137.29 GPa by using a static detection method. Below the transition temperature T_N, the mechanical resonance is found to strongly depend on the magnetic fields with an enormous blueshift of ~3.1% in the magnetic-field-induced phase transition. In addition, we also found that the variation of strain of system $∆ϵ$ was about 1.5 × 10⁻³ during the transition. Our study shows the great potential of two-dimensional magnetic materials in future nanoelectronic applications. Full article

The magnetic, optical, and phonon properties of ion-doped CuAlO${}_2$ nanoparticles on the Cu or Al site are theoretically investigated. The room temperature ferromagnetism in CuAlO${}_2$ nanoparticles can be due to the surface, size, and doping effects. The magnetization increases with the decreasing nanoparticle size. The different radii of the transition metal ion and the host Cu ion lead to compressive strain, to the enhancment of the exchange interaction constants, and to increased magnetization $M_s$ and Curie temperature $T_C$. By substitution with Mn or Cr on the Al site, tensile strain, a decrease in $M_s$, and an increase in dopants are observed. The size and ion-doping influence on the band-gap energy is also discussed. The phonon energy $\omega$ decreases, whereas the phonon damping $\gamma$ increases with increasing temperature and decreasing NP size. They show a kink around $T_C$ ∼ 400 K. The behavior of $\omega$ and $\gamma$ for different ion dopings is observed. Full article

Faraday isolators are the inherent components of complex laser systems. The isolation degree is essentially determined by the effects that occur in its magneto-optical element, so the choice of material from which it is made is very important. The principal approaches to choosing a magneto-optical material for Faraday isolators are addressed. Characteristic features of materials for Faraday devices operating in laser radiation with high average and high peak power are considered. Some trends in magneto-optical ceramics and the advantages and shortcomings of a number of ceramic samples are analyzed. Using the proposed approaches and recommendations will allow to create devices with unique characteristics for any wavelength range for different practical applications. Full article

Granular films SiO₂(Co) exhibit unusual magnetic and magnetotransport properties which are strongly dependent on the composition of the film and material of a substrate. For example, the injection magnetoresistance (IMR) coefficient reaches a giant (GIMR) value of 10⁵% at room temperature in SiO₂(Co) films on an n-GaAs substrate. However, the IMR effect is negligible in the case of a similar granular film deposited on the n-Si substrate. In this report, the structural and magnetic properties of granular film SiO₂(Co) on Si substrate are studied with the aim to understand the cause of the difference in IMR coefficients for SiO₂(Co) thin film deposited on n-GaAs and on n-Si substrates. Investigations were carried out using complementary methods of Polarized Neutron Reflectometry, Grazing Incidence Small-Angle X-ray Scattering, X-ray Reflectometry, Scanning Electron Microscope, and SQUID magnetometry. It is shown that the interface layer between the granular film and Si substrate exhibits metallic rather than magnetic properties and eliminates the GIMR effect. This interface layer is associated with the Si diffusion to Co nanoparticles and the formation of the metallic cobalt silicides. Full article

A novel multi-channel barcode module was developed by using chiral co-crystals which contain field-induced SMM behavior and different emission bands. The chiral co-crystals [Zn(H₂L)Dy(DBM)₂]₄(ClO₄)₄⋅9CH₃OH⋅H₂O (1a) and [Zn(H₂L)Dy(DBM)₂]₄(ClO₄)₄⋅8CH₃OH⋅0.5H₂O (1b) (H₄L = 2,2′-[1,2-ethanediylbis[(hydroxyethylimino)methylene]]bis[6-methoxy-4-methyl-phenol], HDBM = dibenzoylmethane) were obtained through one-pot reaction of Zn^II and Dy^III with the achiral ligands H₄L and HDBM. X-ray single crystal diffraction and CD spectroscopy confirmed that they are enantiomers crystallized in P4₃ (1a) and P4₁ (1b), both consisting of two ∆-[Zn(H₂L)Dy(DBM)₂]⁺ cations, two Λ-[Zn(H₂L)Dy(DBM)₂]⁺ cations and four (ClO₄)⁻ anions. The presence of Dy^III ions endow them with the property of field-induced slow magnetic relaxation. The relatively low energy barrier of 35.0(9) K for complex 1 may be due to the poor axiality of the ligand field caused by the long Dy-O_phenoxy bond lengths and the small O_phenoxy-Dy-O_phenoxy bond angles. Moreover, when the organic ligands H₄L (λ_ex = 350 nm) and Dy^III (λ_ex = 420 nm) are excited, different emission spectra are observed. Full article

Ti-doped maghemite nanoparticles of average crystallite size 12.9 nm were synthesized using the sol–gel method. The XRD profile mainly showed the presence of maghemite phase with very small phases of TiO₂ (rutile and anatase). Magnetization hysteresis loops of the nanoparticles were obtained between −4 T to +4 T at temperatures of 2, 10, 30, 50, 70, 100, 150, 200, and 300 K under field cooling (FC) of 1, 2, 3, and 4 T and zero-field cooling conditions (ZFC). The coercivity displayed nonmonotonic field dependence while it decreased sharply with temperature and vanished at 150 K at all fields. Horizontal hysteresis loop shifts were observed in the 2–150 K temperature range in both the ZFC and FC conditions. The exchange bias effect became negligible in both ZFC and FC states above 50 K. Magnetization vs. applied field measurements were conducted in both ZFC and FC cooled conditions at several temperatures in the range of 2–400 K, with spin freezing being observed below 50 K. The exchange bias effect obtained below 50 K is suggested to be attributed to the competing roles of the long-range dipolar and short-range exchange coupled interactions. Full article

Nanoparticles of Co-doped copper ferrite, ${\mathrm{Cu}}_{0.75}{\mathrm{Co}}_{0.25}{\mathrm{Fe}}_2{\mathrm{O}}_4$, were successfully synthesized by hydrothermal method. The preparation conditions were optimized to produce small nanoparticles with crystallite size of 20 nm that fall into the single-domain regime. The influence of Co-doping on the structure and magnetic properties of pure copper ferrite, ${\mathrm{CuFe}}_2{\mathrm{O}}_4$, was investigated. The prepared ferrite nanoparticles were found to be in a single structural phase with a spinel-type structure, according to the XRD and FT-IR measurements. When compared to pure Cu ferrite, the addition of Co increased the lattice constant and decreased the density. The TEM results confirmed the spherical morphology of the prepared ferrite nanoparticles. For the entire temperature range of the ferrite nanoparticles, the magnetization measurements showed a single ferrimagnetic phase. It was observed that the coercivity and remanent magnetization increased with decreasing temperature. Magnetic anisotropy was found to increase with Co-doping in comparison to pure Cu ferrite. The ZFC–FC magnetization curves showed that the blocking temperature ($T_B$) of the prepared nanoparticles is above room temperature, demonstrating that they are ferrimagnetic at room temperature and below. Additionally, it was found that decreasing the magnetic field lowers $T_B$. The FC curves below $T_B$ were observed to be nearly flat, indicating spin-glass behavior that might be attributed to nanoparticle interactions and/or surface effects such as spin canting and spin disorder. Full article

The study reports the synthesis and characterization of the magnetic and magnetocaloric effects of metal-oxide (MO) modified La_0.7Ca_0.3MnO₃ perovskites manganite. The powder composite samples, with a nominal composition of (1 − x)La_0.7Ca_0.3MnO₃-xMO (Wt.% x = 0.0, 2.5, 5.0), were prepared using the facile autocombustion method, followed by an annealing process. The phase purity and structure were confirmed by X-ray diffraction. Temperature and field-dependent magnetization measurements and Arrott analysis revealed mixed first- and second-order phase transition (ferromagnetic to paramagnetic) in composite samples. The phase transition temperature shifted to lower temperatures with the addition of MO in the composite. A large magnetic entropy change (4.75 JKg⁻¹K⁻¹ at 1T and 8.77 JKg⁻¹K⁻¹ at 5T) was observed in the La_0.7Ca_0.3MnO₃ (LCMO) sample and was suppressed, due to the presence of the MO phase in the composite samples. On the other hand, the addition of MO as a secondary phase in the LCMO samples enhanced their relative cooling power (RCP). The RCP of all composite samples increased with respect to the pristine LCMO, except for LCMO–5%NiO. The highest RCP value of 267 JKg⁻¹ was observed in LCMO–5%CuO samples, which was 23.4% higher than the 213 JKg⁻¹ observed for the pure LCMO at a magnetic field of 5T. The enhanced RCP of these composites makes them attractive for potential refrigeration applications. Full article

Complexes [Fe(X-salEen)₂]BPh₄·DMF, with X = Br (1), Cl (2), and F (3), were crystallised from N,N′-dimethylformamide with the aim of understanding the role of a high boiling point N,N′-dimethylformamide solvate in the spin crossover phenomenon. The counter ion was chosen for only being able to participate in weak intermolecular interactions. The compounds were structurally characterised by single crystal X-ray diffraction. Complex 1 crystallised in the orthorhombic space group P2₁2₁2₁, and complexes 2 and 3 in the monoclinic space group P2₁/n. Even at room temperature, low spin was the predominant form, although complex 2 exhibited the largest proportion of the high-spin species according to both the magnetisation measurements and the Mössbauer spectra. Density Functional Theory calculations were performed both on the periodic solids and on molecular models for complexes 1–3 and the iodide analogue 4. While all approaches reproduced the experimental structures very well, the energy balance between the high-spin and low-spin forms was harder to reproduce, though some calculations pointed to the easier spin crossover of complex 2, as observed. Periodic calculations with the functional PBE led to very similar ΔE_HS-LS values for all complexes but showed a preference for the low-spin form. However, the single-point calculations with B3LYP* showed, for the model without solvate, that the Cl complex should undergo spin crossover more easily. The molecular calculations also reflected this fact, which was more clearly defined when the cation–anion–solvate model was used. In the other models there was not much difference between the Cl, Br, and I complexes. Full article