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Reactions of 12H-quinoxaline[2,3-b]phenoxazine (QOPO) derivatives with the CoII and ZnII hexafluoroacetylacetonates accompanied by protonation of the starting bases result in stable complexes [QOPOH]+[M(hfac)3]− whose structure was determined by X-ray diffraction and by 1H and 15N NMR spectroscopy. The complexes are characterized by long-wavelength absorption (560–664 nm) and fluorescence in the red region (λfl = 674–805 nm). The relative energies of the protonated tautomers N(14)—H and N(7)—H were determined using the results of B3LYP–D3BJ/6-311G++(d,p) density functional calculations with inclusion of D3BJ dispersion correction. A SQUID magnetometry study of the static and dynamic magnetic properties of the CoII complex revealed that it behaves as a field-induced single-ion magnet. [ABSTRACT FROM AUTHOR]

We investigate the effect of an applied magnetic field on the entire HDDR process using a customized reactor vessel and a warm-bore superconducting magnet. We analyzed the resulting properties produced at both a 0 applied field and a 2 Tesla applied field. We show that the application of a magnetic field throughout the HDDR process results in powders that exhibit a greater level of anisotropy compared to their ambient field counterparts. [ABSTRACT FROM AUTHOR]

The interlayer interactions in multilayer systems with a non-magnetic semimetallic interlayer are great of interest. The magnetic and structural properties of the DyxCo1-x/Bi/Py systems (17 < x < 26 at.%) have been studied. The temperature dependences of magnetization in the range 4.2–300 K were measured for the first time. The influence of the bismuth interlayer thickness on the exchange interaction between the DyCo and Py layers was found as well as the critical value of its thickness. The obtained atypical value of the period of exchange bias oscillations was explained by the formation of bismuth compounds with dysprosium–pnictogenides at bismuth thicknesses below the critical value. The interface was investigated by spectral ellipsometry in the range 2–5 eV. The information on the structure of the surface obtained by atomic force microscopy was used to create a multilayer model for fitting experimental ellipsometric data. Analysis of the optical properties showed that pnictogenide Dy3Bi2 is formed at the interface, which affects the general magnetic state of the samples studied. [ABSTRACT FROM AUTHOR]

We investigated the magnetic properties of the antiferromagnetic (AFM) topological insulator MnBi 2 Te 4 with a partial substitution of Mn atoms by non-magnetic elements (A IV = Ge, Pb, Sn). Samples with various element concentrations (10–80%) were studied using SQUID magnetometry. The results demonstrate that, for all substitutes the type of magnetic ordering remains AFM, while the Néel temperature (T N ) and spin-flop transition field (H SF ) decrease with an increasing A IV = Ge, Pb, Sn concentration. The rate of decrease varies among the elements, being highest for Pb, followed by Sn and Ge. This behavior is attributed to the combined effects of the magnetic dilution and lattice parameter increase on magnetic properties, most prominent in (Mn 1 − x Pb x )Bi 2 Te 4 . Besides this, the linear approximation of the experimental data of T N and H SF suggests higher magnetic parameters for pure MnBi 2 Te 4 than observed experimentally, indicating the possibility of their non-monotonic variation at low concentrations and the potential for enhancing magnetic properties through doping MnBi 2 Te 4 with small amounts of nonmagnetic impurities. Notably, the (Mn 1 − x Pb x )Bi 2 Te 4 sample with 10% Pb substitution indeed exhibits increased magnetic parameters, which is also validated by local-probe analyses using ARPES. Our findings shed light on tailoring the magnetic behavior of MnBi 2 Te 4 -based materials, offering insights into the potential applications in device technologies. [ABSTRACT FROM AUTHOR]

In this study, five Cu-Ni substituted cobalt ferrite nanoparticles, i.e., Co0.8Ni0.2Fe2O4; Cu0.2Co0.6Ni0.2Fe2O4; Cu0.4Co0.4Ni0.2Fe2O4; Cu0.6Co0.2Ni0.2Fe2O4 and Cu0.8Ni0.2Fe2O4, have been prepared using an eco-friendly sol–gel autocombustion process. The physicochemical characterization results derived from Fourier transform infrared (FTIR) spectroscopy, x-ray powder diffraction (XRPD), field emission scanning electron microscopy (FESEM), differential thermal analysis (DTA) and thermogravimetric analysis (TGA) have confirmed that the ferrite synthesized powders are pure and are formed by homogeneous crystallites varying in size from 19.96 nm to 24.94 nm. In addition, the nanosized ferrite cubic spinel basic framework has excellent stability versus copper substitution and thermal treatment beyond the combustion temperature and with no detection of tetragonal-cubic phase transition. Furthermore, the zero-field-cooled (ZFC)–field-cooled (FC) and magnetization versus magnetic field strength measurements using magnetization-hysteresis superconducting quantum interface device (M-H SQUID) magnetometry have proved the presence of superparamagnetic behavior at room temperature. Also, theoretical calculations of the superparamagnetic parameter have been performed by fitting the Langevin function to the M-H (300 K) data. The results indicate their significant dependence on both crystallite size and impact of copper composition. Indeed, during the substitution process, a decrease has been observed in remanence, saturation magnetization, coercivity, blocking temperature and magnetocrystalline values. The complex impedance spectroscopy (CIS) study has highlighted the best electrical conductivity value 18.07 × 10–3 S cm−1 associated with the lowest Ea = 0.360 eV of Cu0.8Ni0.2Fe2O4 at 373 K. The excellent magnetic and electrical features of the synthesized nanosized Cu-Ni substituted cobalt ferrites enable them to be applied in various nanotechnological fields of modern life. [ABSTRACT FROM AUTHOR]

We investigate the effect of an applied magnetic field on the entire HDDR process using a customized reactor vessel and a warm-bore superconducting magnet. We analyzed the resulting properties produced at both a 0 applied field and a 2 Tesla applied field. We show that the application of a magnetic field throughout the HDDR process results in powders that exhibit a greater level of anisotropy compared to their ambient field counterparts.

Solid-state wafers are indispensable components in material science as substrates for epitaxial homo- or heterostructures or carriers for two-dimensional materials. However, reliable determination of magnetic properties of nanomaterials in volume magnetometry is frequently affected by unexpectedly rich magnetism of these substrates, including significant magnetic anisotropy. Here, we describe a simplified experimental routine of magnetic anisotropy assessment, which we exemplify and validate for epi-ready sapphire wafers from various sources. Both the strength and the sign of magnetic anisotropy are obtained from carefully designed temperature-dependent measurements, which mitigate all known pitfalls of volume SQUID magnetometry and are substantially faster than traditional approaches. Our measurements indicate that in all the samples, two types of net paramagnetic contributions coexist with diamagnetism. The first one can be as strong as 10% of the base diamagnetism of sapphire [−3.7(1) × 10−7 emu/gOe], and when exceeds 2%, it exhibits pronounced magnetic anisotropy, with the easy axis oriented perpendicularly to the face of c-plane wafers. The other is much weaker, but exhibits a ferromagnetic-like appearance. These findings form an important message that nonstandard magnetism of common substrates can significantly influence the results of precise magnetometry of nanoscale materials and that its existence must be taken for granted by both industry and academia. [ABSTRACT FROM AUTHOR]

We investigated the magnetic properties of the antiferromagnetic (AFM) topological insulator MnBi2Te4 with a partial substitution of Mn atoms by non-magnetic elements (AIV = Ge, Pb, Sn). Samples with various element concentrations (10–80%) were studied using SQUID magnetometry. The results demonstrate that, for all substitutes the type of magnetic ordering remains AFM, while the Néel temperature (TN) and spin-flop transition field (HSF) decrease with an increasing AIV = Ge, Pb, Sn concentration. The rate of decrease varies among the elements, being highest for Pb, followed by Sn and Ge. This behavior is attributed to the combined effects of the magnetic dilution and lattice parameter increase on magnetic properties, most prominent in (Mn1−xPbx)Bi2Te4. Besides this, the linear approximation of the experimental data of TN and HSF suggests higher magnetic parameters for pure MnBi2Te4 than observed experimentally, indicating the possibility of their non-monotonic variation at low concentrations and the potential for enhancing magnetic properties through doping MnBi2Te4 with small amounts of nonmagnetic impurities. Notably, the (Mn1−xPbx)Bi2Te4 sample with 10% Pb substitution indeed exhibits increased magnetic parameters, which is also validated by local-probe analyses using ARPES. Our findings shed light on tailoring the magnetic behavior of MnBi2Te4-based materials, offering insights into the potential applications in device technologies.

Electronics and soft robotics demand the development of a new generation of hybrid materials featuring novel properties. Among these, remarkable mechanical properties are required to sustain mechanical stresses, and electrical and magnetic properties are essential to design the devices' interface. In this study, a hybrid material is presented, consisting of a spider silk thread, providing mechanical robustness, coated with a layer of a magnetostrictive FeCo alloy, which ensures both electrical conductivity and stress‐sensitive magnetic properties. The durability and the homogeneity of the composite are validated, as well as its ability to respond to magnetic and mechanical stimuli. Despite the coating, the soft nature of the silk and its mechanical performances are preserved. The magnetic study reveals that the magnetic behavior of the film is strongly affected by the silk thread–FeCo layer interaction, especially under mechanical stresses. Indeed, when the composite is subjected to tensile strain, the magnetic signal changes accordingly, indicating that the layer–silk interaction is maintained and can be exploited to reveal the tensional state of the sample even under severe cycles. Therefore, the presented hybrid material is a flexible fiber with properties that are suitable for magneto‐electronics applications, e.g., magnetic actuators as well as strain/stress sensors. [ABSTRACT FROM AUTHOR]

As our societal need for materials and energy has grown, so has our need for catalyst processes in hydrogen production. A major function in these applications, for both homogenous and heterogeneous catalysis processes, is the synthesis of an active metal catalyst. It must first be soluble to control the physical properties of the metal being used. Recent work in metal precursors has begun to turn toward these metal carboxylate types of material. Structural models are proposed for bismuth 2-ethylhexanoate and 2,2-dimethyloctanoate and cerium 2-ethylhexanoate. The bismuth compounds have been characterized at different ratios of bismuth to carboxylate as solutions of the free acids. Their structures are most consistent with a Bi 4 (RCO 2) 12 motif where the Bi ions are arranged in a flattened tetrahedron with Bi – Bi distances of about 4.3 Å. There is evidence for Bi – O – Bi linkages at low free acid concentrations. The cerium compound is most consistent with a linear tetracerium molecule where the Ce – Ce distances repeat at about 4.3 Å out to 16.4 Å. The models were generated by analogy with known crystal structures and compared to high-energy x-ray scattering data. To further evaluate the models, DFT calculations were made, and the equilibrium geometries were compared. The vibrational spectra calculated from those geometries are presented and compared to the experimental results. Magnetization vs. temperature data was collected on the cerium compound, and its behavior was consistent with the proposed model. A geometrical approach to determining the dimensionality and relative positions of the metal ions in these structures is presented. [Display omitted] • Molecular elucidation of bismuth and ceria metal carboxylate complex materials. • Designing of highly active catalysts through specific catalytic precursor materials. • Using FTIR, Raman and HEXRD in conjunction with computation studies to propose plausible molecular structures. [ABSTRACT FROM AUTHOR]

Herein, we report the synthesis and properties of triptycene-based C3v- and Cs-symmetric stable radical trimers. SQUID magnetometry showed the propeller-shaped trimers were both an antiferromagnetic equilateral triangle spin system with small spin-spin interaction J/kB ~ -120 K and -106 K, leading to ca. 4/6 coexistence of the doublet/quartet states in thermal equilibrium at room temperature. The trimers exhibited characteristic NIR absorption bands reaching 1000 nm, which was solely ascribed to the triradical in the doublet state by variable-temperature spectroscopic studies and quantum chemical calculations. Taking advantage of the spin-specific absorption feature, we found that the triradicals in the low-spin state undergo symmetry-breaking charge transfer, while those in the high-spin state fall into a monomer-like excited state., (© 2024 Wiley‐VCH GmbH.)

Four compounds are synthesized by the reactions of rare-earth metal(III) nitrates with 2-mercaptopyridine-N-oxide (HSC5H4NO) in water-alkaline solutions: [Pr2(SC5H4NO)6(H2O)2] (I), [Tb2-(SC5H4NO)6(H2O)2] (II), [Ho2(SC5H4NO)6(H2O)2] (III), and [Er2(SC5H4NO)6(H2O)2] (IV). Their synthesis and results of X-ray diffraction studies are presented. Each metal ion in the binuclear complexes forms the octacoordinated structure including two SC5H4NO ligands, which coordinate each metal ion (3+) via the chelate mode (through S and O), two bridging oxygen atoms belonging to two SC5H4NO, and two molecules of coordination water. The product χT and effective magnetic moment (μeff) remain unchanged in the synthesized complexes in the temperature range from 300 to 150 K as found by SQUID magnetometry. At T < 150 K in complexes I (Т < 30 K) and II (T < 50 K), μeff decreases with decreasing temperature, which possibly indicates a magnetic transition and an antiferromagnetic interaction between the Pr3+ and Tb3+ ions. An increase in μeff with decreasing temperature and a sharp decrease at T < 10 K are observed in complex III, whereas in complex IV μeff increases smoothly with decreasing temperature. This can indicate the appearance of ferromagnetic correlations in complex IV. No magnetic relaxation response is observed for complex I in the whole frequency range of the alternating field (AC) HAC from 0.2 to 1400 Hz both in the bias field and without it. The field dependences of the magnetic moment at 2 and 5 K для complexes II–IV are characteristic of paramagnetics at these temperatures. At T = 2 K the samples exist in the same spin state as at T = 300 K: cooling does not change the spin state of the Tb3+, Ho3+, and Er3+ ions in the complexes. No magnetic hysteresis is observed at low temperatures (2 and 5 K) in these complexes. The dependences of the real and imaginary components of the magnetic susceptibility on the AC frequency for complexes II–IV are obtained in the absence of a direct field (DC) and in the bias field. The Cole-Cole diagrams demonstrate the relaxation mode of the domain wall motion and no shift of a maximum of the imaginary component with changing temperature (tunneling relaxation mechanism) in complexes II–IV. [ABSTRACT FROM AUTHOR]

The properties of the hexagonal P2 sodium cobaltate, Na 0.7 CoO 2 (NCO) phase densified using the conventional and cold sintering methods were investigated, and we demonstrated that the cold sintering method yields NCO with a relative density of over 98 % (compared to 90 % attained after conventional sintering) while maintaining high room temperature conductivity (10−2 Scm−1). In X-ray diffraction, the original P2-phase framework is retained regardless of the sintering process, and the magnetic properties of NCO strongly depend on the densification route. Cold-sintered samples showed a classic paramagnetic response down to 2 K, while conventionally sintered samples developed a spin-glass behaviour below 6 K. The emergence of the spin-glass state on conventionally sintered ceramics was attributed to the enhanced disorder of Co3+ and Co4+ ions. A multitude of complex superstructures associated with Na ordering was identified for both cold and conventionally sintered NCO in electron diffraction. [ABSTRACT FROM AUTHOR]

The deposition of a ferromagnetic layer can affect the properties of high-temperature superconductors underneath. We investigated the influence of ferromagnetic CaRuO3 on the properties of YBa2Cu3O7-x (YBCO) superconducting thin films when the layers are either in direct contact or separated by a barrier layer of 5 nm SrTiO3. Detailed measurements of the magnetic moment of the superconductor and ferromagnet as a function of temperature and magnetic field have been performed using SQUID magnetometry. Magnetometry and relaxation measurements show that the modification of the superconducting properties of YBCO strongly depends on the interaction with the ferromagnetic layer on top. The barrier layer has a significant impact on both the supercon-ducting properties of the YBCO film and the ferromagnetic ordering of CaRuO3. The physical properties mentioned above were discussed in correlation with the materials' structure determined by XRD analysis. [ABSTRACT FROM AUTHOR]

Carbonatite is an igneous rock that is composed mainly of carbonate minerals and silicates. It is recently applied as fertilizer due to its high content of calcite and dolomite. This study presents a physical and chemical characterization of the Spanish River Carbonatite (SRC) and its application as fertilizer is tested. The chemical composition obtained by X-ray fluorescence and Energy Dispersive X-ray analyses indicates that Ca, Fe and Si are the main contained elements. Calcite and SiO2 are the principal mineralogical phases as detected by X-ray diffraction. Fourier transform infrared spectroscopy confirms the presence of calcite, silicates and also organic material and water. It also suggests the presence of vermiculite. Thermal analysis reveals only a one-step reaction that corresponds to the decomposition of calcite. Mössbauer spectroscopy performed at room temperature do not show magnetic order between the iron moments instead it shows Fe2+ and Fe3+ doublets in M1 and M2 octahedral sites belonging to vermiculite. At 50 K, we observe that the isomer shift increases their values due to the second order Doppler shift. SQUID magnetometry measurements reveal that most of the sample contains paramagnetic domains assigned to the silicates and calcite components. However, under low applied fields, a tiny signal for Verwey transition appears at 124 K (suggesting the presence of magnetite) although screened by the strong paramagnetic signal of the main components. The SRC has been tested as potential fertilizer on sweet cucumber (Solanum muricatum) which responded positively to the application to carbonatite as an amendment, expressing itself in high foliar biomass. [ABSTRACT FROM AUTHOR]

In the presented study, manganese ferrite MnFe2O4 nanoparticles were synthesized by applying a modified co-precipitation method based on the decomposition of metallic precursors in a liquid phase environment in the presence of surfactant oleic acid. The synthesized sample was then characterized with X-ray Diffraction XRD , standard and high resolution Transmission Electron Microscopy TEM and Fourier Transform Infrared Spectroscopy FTIR , which revealed that the as-prepared MnFe2O4 particles are monodispersed nanocrystals with an average size of 4.7 nm and well surrounded with dimeric oleic acid coating. The magnetic properties of nanoparticles were first investigated by means of Superconducting Quantum Interference Device SQUID magnetometry. The temperature and field dependent magnetization measurements showed that the MnFe2O4 nanoparticles exhibit superparamagnetic property with zero coercivity at room temperature and thermal irreversibility. The superparamagnetic behavior of MnFe2O4nanoparticles was further confirmed by conducting zero field Mössbauer Spectroscopy measurements on nanoparticle powders. As to fulfill all the requirements like crystallinity, small size and superparamagnetism, the prepared oleic acid coated MnFe2O4 nanoparticles has the potential to be used in biomedical applications like targeted drug delivery, MRI and hyperthermia

Solid-state wafers are indispensable components in material science as substrates for epitaxial homo- or heterostructures or carriers for two-dimensional materials. However, reliable determination of magnetic properties of nanomaterials in volume magnetometry is frequently affected by unexpectedly rich magnetism of these substrates, including significant magnetic anisotropy. Here, we describe a simplified experimental routine of magnetic anisotropy assessment, which we exemplify and validate for epi-ready sapphire wafers from various sources. Both the strength and the sign of magnetic anisotropy are obtained from carefully designed temperature-dependent measurements, which mitigate all known pitfalls of volume SQUID magnetometry and are substantially faster than traditional approaches. Our measurements indicate that in all the samples, two types of net paramagnetic contributions coexist with diamagnetism. The first one can be as strong as 10% of the base diamagnetism of sapphire [−3.7(1) × 10−7 emu/gOe], and when exceeds 2%, it exhibits pronounced magnetic anisotropy, with the easy axis oriented perpendicularly to the face of c-plane wafers. The other is much weaker, but exhibits a ferromagnetic-like appearance. These findings form an important message that nonstandard magnetism of common substrates can significantly influence the results of precise magnetometry of nanoscale materials and that its existence must be taken for granted by both industry and academia.

Iron-gallium borate, Fe x Ga 1− x BO 3 , single crystals have been synthesized by the solution in the melt technique. The exact x -values in the crystals have been determined by X-ray fluorescence analysis and checked by Energy Dispersive X-Ray Spectroscopy. Scanning Electron Microscopy has been used to map distributions of iron and gallium ions in the crystals. The electron magnetic resonance (EMR) spectra as well as field and temperature dependences of the magnetization obtained by SQUID reveal the existence of different magnetic phases in different x ranges, viz. weakly ferromagnetic antiferromagnetic, magnetic cluster and paramagnetic phase. For crystals with 0.32 ≤ x ≤ 0.83, the Néel temperatures, T N , have been determined. The magnetometry of these crystals suggests the existence of another magnetic transition at a temperature well below T N , tentatively ascribed to a Morin type transition. Detailed EMR and SQUID studies of the crystal with x ≈ 0.2 reveal the existence of magnetic nanoclusters showing superparamagnetic behaviour. Using a laboratory developed code based on the Monte-Carlo technique, spatial distributions of dia- and paramagnetic ions in the crystal with x ≈ 0.2 has been visualized and possible cluster sizes have been estimated. • Fe x Ga 1− x BO 3 can be weakly ferro- antiferromagnetic, superpara- or paramagnetic. • Superparamagnetism in magnetically diluted crystals arises from magnetic clusters. • Fe x Ga 1− x BO 3 are promising as fine-tunable materials for advanced applications. [ABSTRACT FROM AUTHOR]

Samples taken from the human brain (Globus Pallidus) have been investigated by physical techniques such as light microscopy, scanning electron microscopy, transmission electron microscopy, Mössbauer spectroscopy and SQUID magnetometry. SEM-EDX/TEM investigation reveals multielemental composition of hematite and magnetite nanocrystals with sizes ranging from 40 nm to 100 nm and hematite microcrystals from 3 μm to 7 μm. Room temperature Mössbauer spectra show quadrupole doublets assigning to hematite and ferrihydrite. SQUID measurements of temperature dependence of the mass magnetic susceptibility between T = 2 – 300 K at DC field B0 = 0.1 T, the field dependence of the mass magnetization taken at the fixed temperature T0 = 2.0 and 4.6 K and the zero-field cooled and field cooled magnetization experiments (ZFCM/FCM) confirm a presence of ferrimagnetic phases such as maghemite and/or magnetite with hysteresis loops surviving until the room temperature. Differences between these measurements from the point of view of iron oxides detected can indicate important processes in human brain and interactions between ferritin as a physiological source of iron and surrounding environment.

The deposition of a ferromagnetic layer can affect the properties of high-temperature superconductors underneath. We investigated the influence of ferromagnetic CaRuO3 on the properties of YBa2Cu3O7-x (YBCO) superconducting thin films when the layers are either in direct contact or separated by a barrier layer of 5 nm SrTiO3. Detailed measurements of the magnetic moment of the superconductor and ferromagnet as a function of temperature and magnetic field have been performed using SQUID magnetometry. Magnetometry and relaxation measurements show that the modification of the superconducting properties of YBCO strongly depends on the interaction with the ferromagnetic layer on top. The barrier layer has a significant impact on both the supercon-ducting properties of the YBCO film and the ferromagnetic ordering of CaRuO3. The physical properties mentioned above were discussed in correlation with the materials’ structure determined by XRD analysis.

We investigated the structural and magnetic properties of 20 nm-sized nanoparticles of the half-doped manganite Ho0.5Ca0.5MnO3 prepared by sol-gel approach. Neutron powder diffraction patterns show Pbnm orthorhombic symmetry for 10 K < T < 290 K, with lattice parameters a, b, and c in the relationship c/√2 < a < b, indicating a cooperative Jahn–Teller effect, i.e., orbital ordering OO, from below room temperature. In contrast with the bulk samples, in the interval 250 < T < 300 K, the fingerprint of charge ordering (CO) does not manifest itself in the temperature dependence of lattice parameters. However, there are signs of CO in the temperature dependence of magnetization. Accordingly, below 100 K superlattice magnetic Bragg reflections arise, which are consistent with an antiferromagnetic phase strictly related to the bulk Mn ordering of a charge exchange-type (CE-type), but characterized by an increased fraction of ferromagnetic couplings between manganese species themselves. Our results show that in this narrow band half-doped manganite, size reduction only modifies the balance between the Anderson superexchange and Zener double exchange interactions, without destabilizing an overall very robust antiferromagnetic state.

A new tert‐buthylthiacalix[4]arene‐based tetranuclear 3d‐4f metal complex with the Mn2Tb2 core has been synthesized and its molecular and crystal structures have been studied by X‐ray diffraction. The complex geometry is similar to that of the earlier synthesized tert‐buthylthiacalix[4]arene‐based M2Ln2 complexes with M=Mn(II), Co(II), and Ln=Gd, Pr, Eu, but unlike those systems, it exhibits intricated cooperative low‐temperature magnetic properties arising from the presence of intercluster interactions. At T<8.5 K the complex shows weak spin‐canted ferromagnetism and field induced metamagnetic phase transition. The paramagnetic behavior observed at temperatures higher than 8.5 K is similar to that previously reported for the Mn2Gd2 complex, this being indicative of the existence of competitive ferro‐ and antiferromagnetic intracluster interactions. [ABSTRACT FROM AUTHOR]

We investigated the heating abilities of magnetic nanoparticles (MNPs) in a high-frequency magnetic field (MF) as a function of surface coating and size. The cobalt ferrite MNPs were obtained by a hydrothermal method in a water–oleic acid–ethanol system, yielding MNPs with mean diameter of about 5 nm, functionalized with the oleic acid. By applying another cycle of hydrothermal synthesis, we obtained MNPs with about one nm larger diameter. In the next step, the oleic acid was exchanged for 11-maleimidoundecanoic acid or 11-(furfurylureido)undecanoic acid. For the heating experiments, all samples were dispersed in the same solvent (dichloroethane) in the same concentration and the heating performance was studied in a broad interval of MF frequencies (346–782 kHz). The obtained results enabled us to disentangle the impact of the hydrodynamic, structural, and magnetic parameters on the overall heating capabilities. We also demonstrated that the specific power absorption does not show a monotonous trend within the series in the investigated interval of temperatures, pointing to temperature-dependent competition of the Brownian and Néel contributions in heat release.

Abstract New method for the synthesis of the mononuclear anionic iron dinitrosyl complexes (DNICs) as prospective agents for nitric oxide (NO) chemotherapy of oncological diseases has been developed. Mononuclear anionic DNIC of the composition (N 2 H 5)+[Fe(SR) 2 (NO) 2 ]- with R = 5-nitropyridinyl (I) has been synthesized by the reaction of aqueous solutions of Na 2 [Fе(S 2 O 3) 2 (NO) 2 ] and N 2 H 5 [SС 5 H 3 N 2 O 2 ] salts. The latter one was synthesized by the reduction of bis -(5-nitro-pyridin-2-yl) disulfide with hydrazine hydrate in ethanol at T = 25 °C. Physical-chemical properties of the synthesized complex were studied by X-ray, SEM, IR-, EPR, Mössbauer spectroscopy and SQUID magnetometry in combination with DFT quantum-chemical calculation of molecular structure and spectroscopic properties. Complex I was found to generate NO in proton media without additional activation. The cytotoxicity of I to human tumor cells of various geneses, viz. ovarian cancer SKOV3, colon cancer LS174T and non-small cell lung cancer A549 was discovered for the first time. Graphical abstract Image 1 Highlights • New method for the synthesis of anionic iron dinitrosyl complexes (DNICs) has been developed. • Mononuclear iron complex with 5-nitro-pyridinyl-thiolyl (I) was synthesized. • The molecular structure of the complex I was solved by the methods of solid state chemistry and EPR in solutions. • Complex I has a prolonged NO donor activity under physiological conditions. • The cytotoxicity of I to human tumor cells of various geneses was discovered for the first time. [ABSTRACT FROM AUTHOR]

Carbon-coated nickel (Ni) nanoparticles, Ni@C nanocomposites, have been synthesized using solid-state pyrolysis of nickel phthalocyanine and metal-free phthalocyanine (NiPc) x · (H 2 Pc) 1−x solid solutions, 0 ⩽ x ⩽ 1 . The Ni concentrations in carbon matrix (c Ni ) of the prepared samples continuously varied in the range of 0–3at.% (0–12wt.%). The average nanoparticle size varied within 4–40 nm range. All samples containing single domain Ni nanoparticles exhibit both ferromagnetic and superparamagnetic properties because of the wide range of size distribution. An abrupt drop of saturation magnetization has been observed with decrease in size of Ni nanoparticles from 40 nm to 12 nm. Nearly linear dependence of saturation magnetization on the nanoparticle surface/volume ratio can be interpreted as a result of contact interaction between Ni nanoparticles and the carbon matrix which provides an electron transfer from carbon matrix to nickel. However, further reductions in nanoparticle size increase magnetization growth of which can apparently contribute to the emergence of the giant paramagnetism due to large orbital moments of conductive electrons. The size effects and surface magnetic anisotropy in Ni@C nanocomposites are revealed in the measurements of coercive field, zero-field cooling (ZFC) susceptibility, blocking temperatures and ferromagnetic resonance spectra. Concentration dependencies of ferromagnetic and electron paramagnetic resonance parameters in Ni@C nanocomposites have also been investigated and their peculiarities highlighted. A correlation between concentration dependencies of FMR and SQUID magnetometry parameters, namely between the g -factor curves – g eff , the resonance linewidth – Δ H FMR and coercive field – H c , have been observed. [ABSTRACT FROM AUTHOR]

Homogeneous composites based on poly(methyl methacrylate) and its copolymers with methacrylic acid and on the nitrosyl iron complexes with 2-mercaptobenzimidazole and 2-mercaptobenzthiazole were synthesized. An analysis of the experimental data obtained by the methods of small-angle X-ray diffraction and SQUID magnetometry in combination with the results of quantum chemical calculations showed that the nitrosyl complexes did not retain their initial binuclear structure under the matrix isolation conditions: some complexes decompose to mononuclear ones. The percentage ratio of the dimers and monomers depends on the fraction of the methacrylic acid copolymer in the polymeric matrix and is almost independent of the type of thiol ligand in the iron complex. [ABSTRACT FROM AUTHOR]

Homogeneous composites based on poly(methyl methacrylate) and its copolymers with methacrylic acid and on the nitrosyl iron complexes with 2-mercaptobenzimidazole and 2-mercaptobenzthiazole were synthesized. An analysis of the experimental data obtained by the methods of small-angle X-ray diffraction and SQUID magnetometry in combination with the results of quantum chemical calculations showed that the nitrosyl complexes did not retain their initial binuclear structure under the matrix isolation conditions: some complexes decompose to mononuclear ones. The percentage ratio of the dimers and monomers depends on the fraction of the methacrylic acid copolymer in the polymeric matrix and is almost independent of the type of thiol ligand in the iron complex. [ABSTRACT FROM AUTHOR]

Operando magnetic susceptibility measurements of the cathode material LiNi 0.6 Mn 0.2 Co 0.2 O 2 during repetitive electrochemical cycling enable a continuous and volume sensitive monitoring of the transition metal oxidation states. Upon charging a simultaneous oxidation of Co 2+ - and Ni 2+ -ions down to a Li-content of x = 0.53 occurs, followed by an exclusive oxidation of Ni 3+ -ions for 0.53 > x > 0.21 . In the low Li concentrations regime x < 0.21 Co 3 + -ions were found to be involved in the charge compensation process although a sufficient amount of Ni 3+ -ions is still present in the cathode material. While the oxidation process of Ni 2+ - and Co 2+ -ions is reversible, the Ni 3+ - and Co 3+ -ion oxidation process is found to be at least partially irreversible. [ABSTRACT FROM AUTHOR]

Deposits of iron oxides in the human brain (globus pallidus) are visible under electron microscopy as object of regular and or/irregular shape but giving sharp diffraction patterns in the transmission mode. The SQUID magnetometry reveals that the magnetization curves decline form an ideal Langevin function due to the dominating diamagnetism of organic tissue. The fitting procedure yields the quantitative characteristics of the overall magnetization curves that were further processed by statistical multivariate methods

Methods improving the chemical and physical stability of magnetic nanoparticles are important in diverse research disciplines such as catalysis, magnetic resonance imaging, biomedicine, and bioseparation. It is essential that defined nanomaterial characteristics remain unchanged from the start of the nanoparticle production to their final application. A simple, fast and reliable strategy based on a thermal decomposition approach was established to design highly and uniformly loaded iron oxide-shell silica-core nanocomposites. They are formed by maghemite nanoparticles (8.4 ± 1.0 nm) uniformly deposited on mesoporous silica nanoparticles (381 nm ± 111 nm). Their magnetic properties as well as chemical, and mechanical stability were verified by SQUID magnetometry, Raman microspectroscopy, and electron microscopy (SEM and TEM), respectively. The produced superparamagnetic nanocomposites were stable over several months. The coating with organosilanes enables the transfer from nonpolar to aqueous phase which makes the magnetic nanocomposites also applicable for life sciences. [ABSTRACT FROM AUTHOR]

Ni-Zn and Ni-Zn-Co ferrite powders with nominal compositions Ni 0.5 Zn 0.5 Fe 2 O 4 and Ni 0.5 Zn 0.3 Co 0.2 Fe 2 O 4 were prepared by the solid-state reaction synthesis with periodic regrinding during the calcination at 1073 K. The structure of Ni 0.5 Zn 0.5 Fe 2 O 4 and Ni 0.5 Zn 0.3 Co 0.2 Fe 2 O 4 was refined assuming space group F d- 3 m . Scanning electron microscopy revealed the average sizes of the crystalline ferrite particles are 130–630 nm for Ni 0.5 Zn 0.5 Fe 2 O 4 and 140–350 nm for Ni 0.5 Zn 0.3 Co 0.2 Fe 2 O 4 . The room temperature saturation magnetizations are 59.7 emu/g for Ni 0.5 Zn 0.5 Fe 2 O 4 and 57.1 emu/g for Ni 0.5 Zn 0.3 Co 0.2 Fe 2 O 4 . The coercivity of the samples is found to be much larger than that of bulk ferrites and increases with Co introduction. The Curie temperature tends to increase upon Zn substitution by Co, as well. The temperature dependences of magnetization measured using zero-field cooled and field cooled protocols exhibit large spin frustration and spin-glass-like behavior. [ABSTRACT FROM AUTHOR]

Iron, an essential element of the human body, is a significant risk factor, particularly in the case of its concentration increasing above the specific limit. Therefore, iron is stored in the non-toxic form of the globular protein, ferritin, consisting of an apoferritin shell and iron core. Numerous studies confirmed the disruption of homeostasis and accumulation of iron in patients with various diseases (e.g. cancer, cardiovascular or neurological conditions), which is closely related to ferritin metabolism. Such iron imbalance enables the use of magnetic resonance imaging (MRI) as a sensitive technique for the detection of iron-based aggregates through changes in the relaxation times, followed by the change in the inherent image contrast. For our in vitro study, modified ferritins with different iron loadings were prepared by chemical reconstruction of the iron core in an apoferritin shell as pathological model systems. The magnetic properties of samples were studied using SQUID magnetometry, while the size distribution was detected via dynamic light scattering. We have shown that MRI could represent the most advantageous method for distinguishing native ferritin from reconstructed ferritin which, after future standardisation, could then be suitable for the diagnostics of diseases associated with iron accumulation. [ABSTRACT FROM AUTHOR]

The variation of the structural and electronic properties of Li x CoO 2 upon electrochemical Li-extraction was studied over wide range concentration of 1 ≥ x ≥ 0.20 by means of SQUID magnetometry. The ex-situ measurements performed for 13 different compositions were supplemented by operando measurements of the magnetic moment during repetitive electrochemical in-situ cycling of the Li-concentration. From the temperature-dependent measurements an effective magnetic susceptibility with Curie–Weiss behavior and an additional temperature-independent part due to Pauli and Van Vleck magnetism is derived. The increase of the temperature-independent susceptibility with Li-extraction reflects a concomitant increase of the electronic density of states and, in addition, indicates an Anderson-type of the occurring nonmetal–metal transition. The effective magnetic moment reveals that only a fraction of 30% of the charge is transferred to Co upon Li-extraction indicating a complex oxidation behavior involving oxygen. Exposure to ambient atmosphere gives rise to a complete oxidation of Co. The results on the structural variation with Li-concentration are compared with accompanying measurements by X-ray diffraction and by our recent defect studies by positron annihilation. [ABSTRACT FROM AUTHOR]