FeRh-based alloys are unique objects, the study of which allows us to identify new features of first-order magnetic phase transitions. Doping of an alloy often leads to significant changes in its magnetic properties. This paper examines the structural, magnetic, transport and caloric properties of iron-rhodium alloys with different cobalt doping with varying cobalt content (0-1.8 at%). Doping the alloy with less than 2 at% cobalt resulted in a decrease in the phase transition temperature by 200 K. Based on the results obtained, a relationship was established between the magnetic properties and the heterogeneity of the elemental composition of the samples. It was also demonstrated that significant changes in the parameters of the magnetic phase transition of the alloy upon alloying are largely determined by the electronic properties. Considering the sensitivity of the alloy properties to the cobalt content, we develop a novel methodology for quantifying local compositional variations using temperature-dependent measurements, demonstrating its superior sensitivity compared to conventional techniques. The strong correlation between magnetocaloric response and cobalt concentration highlights the importance of precise composition control for applications.

Magnesioferrite (MgFe2O4) spinel nanoparticles were synthesized via the solution combustion method and subjected to annealing at temperatures ranging from 400 degrees C to 800 degrees C to investigate the effect of thermal treatment on their structural and magnetic properties. X-ray diffraction revealed a significant crystallization transition between 500 degrees C and 600 degrees C, with crystallite sizes increasing from approximately 5 nm-25 nm. Mossbauer spectroscopy identified a transition from superparamagnetic to ferrimagnetic behavior, with hyperfine magnetic fields reaching 460-480 kOe in samples annealed above 600 degrees C. Magnetic measurements showed a saturation magnetization of 15-50 emu/g and coercivity ranging from 0 to 120 Oe, depending on annealing temperature. Raman spectroscopy confirmed increased crystallinity and structural ordering at higher temperatures. These results demonstrate that annealing effectively tailors the functional properties of MgFe2O4, enabling its application in magnetic, catalytic, and sensing technologies.

The effect of substitutional 4f-elements on the magnetism of rare-earth compounds RFe2-type with the Laves phase structure is studied to find new multifunctional materials, as well as to define the macro- and microscopic parameters of multicomponent magnets. The crystal structure of (Er,Y,Sm)Fe2 compounds is investigated by X-ray powder diffraction. Detailed information on the magnetic properties of the iron sublattice for multicomponent compounds with three different rare-earth elements is obtained for the first time by means of the 57Fe Mössbauer spectroscopy. The main regularities in the magnitude variation of magnetocaloric effect and magnetostriction (linear, anisotropic and volume) in varying composition of the (Er,Y,Sm)Fe2 compounds are determined.

In this study, we have synthetized a series of citric acid stabilized superparamagnetic iron oxide nanoparticles (CA-SPIONs) with different core sizes in an automated chemical reactor with high repeatability of the nano- particle size and chemical composition. The prepared CA-SPIONs are highly crystalline spherical-shaped particles with the diameters of 3.5 f 0.7, 6 f 1, 9 f 1, and 12 f 2 nm. The valent state of iron oxide was determined by a combination of X-ray photoelectron spectroscopy, UV-Vis spectroscopy, and Mossbauer studies, which confirmed predominantly maghemite formation. Under normal conditions, these nanoparticles exhibit no coercive force and no hysteresis, while saturation magnetization increases from 2 to 61 emu/g along with the increasing core size. Both longitudinal (r1) 1 ) and transverse (r2) 2 ) relaxivities of maghemite hydrosols with different nanoparticle sizes were measured and compared with the same data for the commercial Gd-complex (Gadovist). Magnetic circular dichroism spectroscopy indicated that aggregation occurs in magnetic field, but 9 nm samples slightly aggregate in the fields above 1.0 T, whereas 3.5 nm colloids are stable and do not exhibit aggregation behavior even at 1.5 T. The obtained series were examined in phantom test in clinical 1.5 T MRI scanner, which showed that increasing the particle core size resulted in an enhanced T2 2 contrast, while T1 1 contrast declined. Finally, the smallest CA-SPION colloid nanoparticles with the size of 3.5 nm exhibited significant T1 1 contrast enhancement, comparable with the commercial Gd-complex in water and human plasma as well. The maghemite hydrosol formed by nanoparticles with 3.5 nm size thus has a promising future as a T1 1 MRI contrast agent.

We have studied magnetization process of 260 nm sized cubic Fe3O4 particles below and above the Verwey transition temperature Tv∼ 110 K, by measurements of magnetic first-order reversal curves (FORCs) and high-resolution power neutron diffraction. The FORC diagram exhibits two distinct FORC distribution peaks below Tv, which shift towards the origin, merge into a single peak on heating, whereas only a single FORC peak appears above Tv. Neutron diffraction measurements under magnetic fields revealed a minimum of the magnetic intensity at a magnetic field of ∼−300 Oe, being close to the reversal field where the FORC peak is located. These results were interpreted as due to a reorientation and reversal of a spin vortex core, which accompany a large magnetic irreversibility.

The most important limitation for boron neutron capture therapy of cancer is the selective accumulation of boron compounds in tumor tissues in significant quantities. In this paper, we describe the possibility to use magnetic Ni/Fe nanotubes as carriers for boron delivery. Carborane derivatives containing 10 and 21 boron atoms per molecule were immobilized on Ni/Fe nanotubes by covalent and ionic interactions. Magnetic properties of NTs were investigated by Mössbauer spectroscopy. Structure, element, chemical composition, and morphology of obtained magnetic nanotubes were studied by XRD, SEM-EDA, and FTIR spectroscopy. Results indicate success immobilization of carborane derivatives on Ni/Fe nanotubes and great potential to use them as carriers for boron neutron cancer therapy of cancer.

Reducing the size of a material with a first-order magnetic phase transition to the nanoscale results in a significant change in its physical properties. An example of this behaviour is the FeRh alloy. According to magnetometry results, the nanoparticles of this alloy do not show a transition from the antiferromagnetic to the ferromagnetic state near room temperature. In this work we have measured the magnetic properties and the Mo center dot ssbauer effect for FeRh@FeO composite nanoparticles at different temperatures. An analysis of the results allows us to conclude that superparamagnetic relaxations dominate the formation of the magnetic structure of the nanoparticles. For particle sizes near 10 nm, the antiferromagnetic state is possible near helium temperatures. Further heating contributes to the formation of superparamagnetic behaviour.

The changes in the substituted La0.5Sr0.5FeO3_ & gamma; orthoferrite under vacuum annealing in the temperature range of 200-650 degrees C have been studied by X-ray diffraction analysis, as well as Mo & BULL;ssbauer and Raman spectroscopy. Annealing of the as-prepared ferrite with the rhombohedral structure (R 3 c) resulted in its transition to the cubic one (Pm 3 m) at 650 degrees C. In the as-prepared ferrite being paramagnetic at room temperature, Fe ions were detected in an averaged-valence state between Fe3+ and Fe4+, which was not revealed with a decrease in the temperature down to 85 K. Gradual oxygen loss and an increase in the number of oxygen vacancies took place with an increase in the vacuum annealing temperature. Only Fe3+ ions were present in the ferrite at a vacuum annealing temperature above 500 degrees C. Several Zeeman sextets in the Mo & BULL;ssbauer spectra associated with Fe3+ ions were resulted from the presence of oxygen vacancies and Fe4+ ions in the local environment of Fe3+ ions. The variations in the ratio of the valence states of Fe ions obtained from Mo & BULL;ssbauer data depending on a vacuum annealing temperature allowed determining the content of oxygen in all the investigated samples. The contri-bution of Fe3+ ions that did not have Fe4+ ions and oxygen vacancies in their local environment was shown to increase with a vacuum annealing temperature from 12% (for the as-prepared sample) to 60% (for the sample annealed at 650 degrees C). On a whole, the process taking place under vacuum annealing can be characterized as a variation of the local environment of Fe3+ ions towards a decrease in its distortion. It was found that the width of the peaks of the Raman spectra decreased and their amplitude increased with an increase in the vacuum annealing temperature, which also demonstrated the improvement of the structural perfection of the samples.

Haloalkaliphilic microorganisms are double extremophiles functioning optimally at high salinity and pH. Their typical habitats are soda lakes, geologically ancient yet widespread ecosystems supposed to harbor relict microbial communities. We compared metabolic features and their determinants in two strains of the natronophilic species Dethiobacter alkaliphilus, the only cultured representative of the class “Dethiobacteria” (Bacillota). The strains of D. alkaliphilus were previously isolated from geographically remote Mongolian and Kenyan soda lakes. The type strain AHT1T was described as a facultative chemolithoautotrophic sulfidogen reducing or disproportionating sulfur or thiosulfate, while strain Z-1002 was isolated as a chemolithoautotrophic iron reducer. Here, we uncovered the iron reducing ability of strain AHT1T and the ability of strain Z-1002 for thiosulfate reduction and anaerobic Fe(II) oxidation. Key catabolic processes sustaining the growth of both D. alkaliphilus strains appeared to fit the geochemical settings of two contrasting natural alkaline environments, sulfur-enriched soda lakes and iron-enriched serpentinites. This hypothesis was supported by a meta-analysis of Dethiobacterial genomes and by the enrichment of a novel phylotype from a subsurface alkaline aquifer under Fe(III)-reducing conditions. Genome analysis revealed multiheme c-type cytochromes to be the most probable determinants of iron and sulfur redox transformations in D. alkaliphilus. Phylogeny reconstruction showed that all the respiratory processes in this organism are likely provided by evolutionarily related early forms of unconventional octaheme tetrathionate and sulfite reductases and their structural analogs, OmhA/OcwA Fe(III)-reductases. Several phylogenetically related determinants of anaerobic Fe(II) oxidation were identified in the Z-1002 genome, and the oxidation process was experimentally demonstrated. Proteomic profiling revealed two distinct sets of multiheme cytochromes upregulated in iron(III)- or thiosulfate-respiring cells and the cytochromes peculiar for Fe(II) oxidizing cells. We suggest that maintaining high variation in multiheme cytochromes is an effective adaptive strategy to occupy geochemically contrasting alkaline environments. We propose that sulfur-enriched soda lakes could be secondary habitats for D. alkaliphilus compared to Fe-rich serpentinites, and that the ongoing evolution of Dethiobacterales could retrace the evolutionary path that may have occurred in prokaryotes at a turning point in the biosphere’s history, when the intensification of the sulfur cycle outweighed the global significance of the iron cycle.

The valence states of Fe atoms and the formation of oxygen vacancies in substituted La0.67Sr0.33FeO3−γ orthoferrite have been studied in detail by low-temperature Mössbauer spectroscopy under oxygen removal. It has been shown that the averaged valence state of Fe atoms is not revealed with a decreasing measurement temperature. This makes it possible to reveal Fe4+ ions. The Analysis of the obtained data allows us to conclude that the presence of several Zeeman sextets associated with Fe3+ ions is related to the appearance of oxygen vacancies and Fe4+ ions in the nearest ionic surrounding of Fe ions. Using the Mössbauer data, the number of oxygen vacancies and oxygen ions has been determined for all the studied samples depending on the vacuum annealing temperature.

Sr-doped (00.2) ceramic samples of the lanthanum manganite oxides were obtained via sol-gel method to investigate the influence of doping on structural, magnetic end electronic responses, and their correlations. Synthesized samples of non-stoichiometric compositions are rhombohedral single-phase. After annealing the formation of a phase-separated system as a mixture of orthorhombic phases was found.The R-3c and PnmaI, PnmaII* and PnmaII phases have been studied using Mo spacing diaeresis ssbauer spectroscopy, XRD, SEM analysis and magnetic measurements. The magnetic temperature-concentration phase diagram of La1-xSrxMnO3+delta (x = 0.05, 0.10, 0.20) was obtained. The Jahn-Teller effect or the orbital order breaking, as well as the competition between Mn3+-O2-Mn4+ double-and Mn3+-O2--Mn3+ superexchange interaction was demonstrated under the effect of cation doping compound and interstitial oxygen value (delta). The relaxation character of the Mo spacing diaeresis ssbauer spectra and the type of magnetization dependences revealed nanosized magnetic clusters with fluctuation of their magnetic moment in all perovskite phases. Results are interpreted in terms of matrix - clusters: regions of sample with ferromagnetic type of ordering (cluster) exist in antiferromagnetically or ferromagnetically (with different exchange parameter) ordered matrix. Exchange interaction frustrations of the cluster with the matrix can lead to relaxation behavior of the magnetic moment of the cluster. The clusters size vary from about 3.9 to 5.7 nm. All samples are charac-terized by the presence of particles agglometates with a typical size about 0.4-0.8 mu m; for annealed samples additional non-conducting regions with 80-220 nm in size were found. It is shown that the annealing time significantly affects the production of materials with determined properties and be useful in the applied field in technological processes.

Conducting high-temperature tests on ceramics-containing lithium, which are employed as tritium breeding materials, plays a crucial role in comprehending their ability to withstand degradation and maintain their strength properties throughout operation. From the standpoint of fusion research, it is imperative to grasp these phenomena in order to guarantee the safety and effectiveness of reactors. Additionally, these factors could impact the choice of particular materials and designs for blanket materials. The primary objective of this research is to evaluate alterations in the strength characteristics of ceramics-containing lithium when subjected to high-temperature thermal stability tests, while also preserving the hardness stability and resistance to cracking in ceramics subjected to cyclic tests. Lithium-containing ceramics based on lithium titanate (Li2TiO3), lithium orthosilicate (Li4SiO4), and lithium methacyrconate (Li2ZrO3), having a high structural ordering degree and good strength properties, were chosen as objects for assessing resistance to high-temperature degradation. During the studies, it was discovered that the presence of interphase boundaries in the composition of ceramics linked to the development of impurity phases results in crack resistance growth during long-term high-temperature tests simulating the stress effect on the material. At the same time, an assessment of high-temperature aging as a result of modeling destruction processes showed that ceramics based on lithium metazirconate are the most resistant to degradation of strength properties. By simulating high-temperature aging processes, it became feasible to establish connections between structural alterations resulting from the thermal expansion of the crystal lattice and oxygen migration phenomena occurring at elevated temperatures. These factors collectively contribute to a detrimental reduction in the strength properties of ceramics-containing lithium.

Four samples of natural Ti-bearing garnets from Odihincha, Maimecha-Kotui alkaline province, Krasnoyarsk Krai, Russia, were studied using electron microprobe analysis, X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman and Mössbauer spectroscopy, and thermal analysis. The enthalpies of formation from elements were determined with a high-temperature heat-flux Tian–Calvet microcalorimeter by means of the melt solution calorimetry. The first ever values of $${{\Delta }_{{\text{f}}}}H_{{{\text{el}}}}^{0}$$ (298.15 K) were determined as follows: −5861.1 ± 11.3 kJ/mol for (Ca3.00Na0.02Fe2+0.01) ( $${\text{Fe}}_{{1.42}}^{{3 + }}{\text{Ti}}_{{0.26}}^{{4 + }}$$ Al0.21Mg0.04 $${\text{Fe}}_{{0.03}}^{{2 + }}{\text{Mn}}_{{0.01}}^{{2 + }}$$ )[(Si2.85 $${\text{Fe}}_{{0.13}}^{{3 + }}$$ )O11.92(OH)0.08]; −5915.2 ± 9.0 kJ/mol for Ca3.01( $${\text{Fe}}_{{1.27}}^{{3 + }}{\text{Ti}}_{{0.57}}^{{4 + }}$$ Mg0.05 $${\text{Fe}}_{{0.03}}^{{2 + }}{\text{Mn}}_{{0.01}}^{{2 + }}$$ )[(Si2.69Al0.16 $${\text{Fe}}_{{{\text{0}}{\text{.13}}}}^{{{\text{3 + }}}}{\text{Ti}}_{{{\text{0}}{\text{.01}}}}^{{{\text{4 + }}}}$$ )O11.96(OH)0.04]; −5902.5 ± 9.1 kJ/mol for (Ca2.97 $${\text{Mn}}_{{{\text{0}}{\text{.02}}}}^{{{\text{2 + }}}}{\text{Fe}}_{{{\text{0}}{\text{.01}}}}^{{{\text{2 + }}}}$$ )( $${\text{Fe}}_{{{\text{1}}{\text{.20}}}}^{{{\text{3 + }}}}{\text{Ti}}_{{{\text{0}}{\text{.64}}}}^{{{\text{4 + }}}}$$ Mg0.05 $${\text{Fe}}_{{0.04}}^{{2 + }}$$ )[(Si2.64 $${\text{Fe}}_{{{\text{0}}{\text{.23}}}}^{{{\text{3 + }}}}$$ Al0.11 $${\text{Ti}}_{{0.01}}^{{4 + }}$$ )O11.96(OH)0.04]; and −5945.7 ± 10.2 kJ/mol for (Ca2.90Na0.04 $${\text{Fe}}_{{{\text{0}}{\text{.03}}}}^{{{\text{2 + }}}}{\text{Mn}}_{{{\text{0}}{\text{.02}}}}^{{{\text{2 + }}}}$$ Mg0.01)( $${\text{Fe}}_{{{\text{0}}{\text{.97}}}}^{{{\text{3 + }}}}{\text{Ti}}_{{{\text{0}}{\text{.71}}}}^{{{\text{4 + }}}}$$ Mg0.13Zr0.08 $${\text{Fe}}_{{{\text{0}}{\text{.05}}}}^{{{\text{2 + }}}}$$ ) [(Si2.33 $${\text{Fe}}_{{{\text{0}}{\text{.32}}}}^{{{\text{3 + }}}}{\text{Ti}}_{{{\text{0}}{\text{.24}}}}^{{{\text{4 + }}}}$$ Al0.07)O11.84(OH)0.16]. The standard Gibbs free energies of formation of these garnets were calculated using the values obtained for the formation enthalpies and estimated for the entropies. Also, the enthalpies of formation of the end-members of the isomorphic schorlomite–morimotoite series were derived. The thermodynamic constants were used in quantitative modeling of the stability fields of these minerals.

Iron-containing oxides are the most important functional substance class and find a tremendous variety of applications. An attractive modern application is their use in biomedical technologies as components in systems for imaging, drug delivery, magnetically mediated hyperthermia, etc. In this paper, we report the results of the experimental investigation of submicron Y3Fe5O12 garnet particles obtained in different sizes by solution combustion synthesis (SCS) using glycine organic fuel to discuss the interdependence of peculiarities of the crystal and magnetic structure and size’s influence on its functional magnetothermal performance. A complex study including Mössbauer and Raman spectroscopy accompanied by X-ray diffractometry, SEM, and measurements of field and temperature magnetic properties were performed. The influence of the size effects and perfectness of structure on the particle set magnetization was revealed. The ranges of different mechanisms of magnetothermal effect in the AC magnetic field were determined.

The substituted orthoferrite La0.67Sr0.33FeO3_gamma was studied using scanning electron microscopy, X-ray diffraction (XRD), and Mo center dot ssbauer and Raman spectroscopy. A series of vacuum annealing in the temperature range of 200-650 degrees C was performed, resulting in negligible changes in the crystal structure of samples. The volume of the pseudocubic unit cell increased continuously with raising temperature up to 450 degrees C. It follows from the Mo center dot ssbauer measurements that at room temperature Fe ions were characterized by an averaged-valence state. The vacuum annealing induced oxygen vacancies and changed the averaged-valence state of Fe ions. Sufficiently good correlations among the Mo center dot ssbauer, XRD, and Raman spectroscopy data were obtained.

The paper presents the results of a study of iron oxide nanoparticles obtained by chemical coprecipitation, coated (Fe3O4@Au) and not coated (Fe3O4) with gold, which were subjected to thermal annealing. To characterize the nanoparticles under study, scanning and transmission electron microscopy, X-ray diffraction, and Mössbauer spectroscopy on 57Fe nuclei were used, the combination of which made it possible to establish a sequence of phase transformations, changes in morphological and structural characteristics, as well as parameters of hyperfine interactions. During the studies, it was found that thermal annealing of nanoparticles leads to phase transformation processes in the following sequence: nonstoichiometric magnetite (Fe3−γO4) → maghemite (γ-Fe2O3) → hematite (α-Fe2O3), followed by structural ordering and coarsening of nanoparticles. It is shown that nanoparticles of nonstoichiometric magnetite with and without gold coating are in the superparamagnetic state with a slow relaxation rate. The magnetic anisotropy energy of nonstoichiometric magnetite is determined as a function of the annealing temperature. An estimate was made of the average size of the region of magnetic ordering of Fe atoms in nonstoichiometric magnetite, which is in good agreement with the data on the average sizes of nanoparticles determined by scanning electron microscopy.

The article presents the results of evaluating the applicability of various types of iron-containing nanoparticles in magnetic hyperthermia, as well as determining the degradation resistance of nanoparticles. The objects of study were iron-containing nanoparticles obtained by chemical precipitation and subsequent modification with gold, gadolinium, and neodymium. The main methods for studying the properties of the synthesized nanoparticles were transmission electron microscopy, X-ray phase analysis, and Mössbauer spectroscopy. Evaluation of the efficiency of the use of the synthesized nanoparticles in magnetic hyperthermia showed that Fe3O4@GdFeO3 nanoparticles, for which the specific absorption rate was more than 120 W/g, have the highest efficiency. An assessment of the resistance of the synthesized nanoparticles to corrosion in water at different temperatures showed that Fe2O3@NdFeO3 and Fe3O4@GdFeO3 nanoparticles have the highest resistance to degradation. It has been established that in the case of the initial Fe3O4 nanoparticles, the degradation processes are accompanied by partial destruction of the particles, followed by amorphization and destruction, while for Fe2O3@NdFeO3 and Fe3O4@GdFeO3 nanoparticles, the degradation processes proceed much more slowly, due to the presence of interfacial boundaries, which slow down the corrosion processes. The obtained results of corrosion tests in aqueous media make it possible to predict the area and time frame of applicability of iron-containing nanoparticles when using them in the biomedical direction, as well as to determine storage conditions.

A potassium salt of the N2S2O2-coordination Fe(III) anion K[Fe(5Cl-thsa)2] (1) (5Cl-thsa - 5-chlorosalicylaldehyde thiosemicarbazone) is synthesized and characterized structurally and magnetically over a wide temperature range. Two polymorphs of salt 1 characterized by the common 2D polymer nature and assigned to the same orthorhombic Pbcn space group have been identified. The molecular structure of the minor polymorph of 1 was solved and refined at 100, 250, and 300 K is shown to correspond to the LS configuration. The dominant polymorph of 1 features K+ cations disordered over a few crystallographic sites, while the minor polymorph includes fully ordered K+ cations. The major polymorph exhibits a complete three-step cooperative spin-crossover transition both in the heating and cooling modes: The first step occurs in a temperature range from 2 to 50 K; the second abrupt hysteretic step occurs from 200 to 250 K with T1/2 = 230 K and a 6 K hysteresis loop. The third gradual step occurs from 250 to 440 K. According to 57Fe Mössbauer, XRPD, and EXAFS data, the spin-crossover transition for the dominant polymorph is quite peculiar. Indeed, the increase in the HS concentration by 57% at the second step does not result in the expected significant increase in the iron(III)-ligand bond lengths. In addition, the final step of the spin conversion (ΔγHS = 26%) is associated with a structural phase transition with a symmetry lowering from the orthorhombic (Pbcn) to the monoclinic (P21/n) space group. This nontrivial phenomenon was investigated in detail by applying magnetization measurements, electron spin resonance, 57Fe Mössbauer spectroscopy, and DFT calculations. These results provide a new platform for understanding the multistep spin-crossover character in the Fe(III) thsa-complexes and related compounds.