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Electronic topology in metallic kagome compounds is under intense scrutiny. We present transport experiments in ${\mathrm{Na}}_{2/3}\mathrm{Co}{\mathrm{O}}_{2}$ in which the Na order differentiates a Co kagome sublattice in the triangular $\mathrm{Co}{\mathrm{O}}_{2}$ layers. Hall and magnetoresistance (MR) data under high fields give evidence for the coexistence of light and heavy carriers. At low temperatures, the dominant light carrier conductivity at zero field is suppressed by a $B$-linear MR, suggesting Dirac-like quasiparticles. Lifshitz transitions induced at large $B$ and $T$ unveil the lower mobility carriers. They display a negative ${B}^{2}$ MR due to scattering from magnetic moments likely pertaining to a flat band. We emphasize an analogy with heavy fermion physics.

We have implanted ZnO thin film with 40 keV Fe+ ions to a high fluence of 1.25 × 1017 ions/cm2. Elemental and magnetic phase compositions were investigated by XRD, XPS, CEMS, and VSM methods. The Fe-implanted ZnO film reveals strong ferromagnetism at room temperature. The implanted iron ions are found in different valence states of Fe2+ and Fe3+. It was attributed to the formation of paramagnetic and ferromagnetic iron-based phases. The ferromagnetism is explained with the formation of a magnetic ordered solution of iron ions in ZnO matrix. Post-implantation annealing in a high vacuum results in the decrease of magnetism due to the formation of magnetite nanoparticles.

The unusual temperature behavior of the electron spin resonance (ESR) spectra and magnetic properties are experimentally observed in copper(II) complexes with a dendritic ligand based on the Boltorn H30 polymer (Perstorp Specialty Chemicals AB, Sweden) functionalized with fumaric acid residues in a molar ratio of 1:6. The ESR spectra at low temperatures show signs of transition to higher spin states at temperatures below 8-10 K, and the temperature dependences of the integral ESR signal intensities and magnetic susceptibility show the positive deviation from the Curie-Weiss law, thereby pointing to the presence of ferromagnetic exchange interactions in the system under study. The values of the exchange interaction parameters are calculated by quantum-chemical simulation of the possible structure of the copper(II) complex when assuming the formation of trinuclear coordination sites embedded in the hyperbranched polymer structure. The results of density functional theory calculations indicate the possibility of ferromagnetic exchange through carboxylate bridges in the trinuclear magnetic clusters, and the calculated values of the exchange interaction parameters make it possible to construct theoretical curves of the temperature dependence of the effective magnetic moment, which satisfactorily fit the experimental data, especially considering that polymers are characterized by disperse molecular weights and chemical structures.

We studied the magnetocaloric effect in a single crystal GdTiO3. Single crystal GdTiO3 had a second order phase transition from a paramagnetic to ferrimagnetic state at 33 K. The maximum entropy change of - Δ S = 0.10 J/cm3 K was observed in a 5 T field at the transition temperature. A small anisotropy was found in the magnetization and specific heat in low magnetic fields. The magnetization showed no hysteresis. Temperature dependencies of entropy, which are important for analyzing the refrigeration cycle, were calculated from the magnetization and specific heat measurements. These results indicate that GdTiO3 has the potential for applications as a magnetic refrigerant for hydrogen liquefaction.

The structural and magnetic properties of YbMnO3 and Yb0.82Sr0.18MnO3 multiferroics were studied by neutron powder diffraction (NPD), magnetometry and electron spin resonance (ESR) technics in a wide temperature range. Neutron diffraction measurements showed that the substitution of ytterbium ions with strontium ions in hexagonal h - YbMnO3 (space group P63cm) leads to the destabilization of the crystal structure of the last compound and appearance of the mixture of three phases with different structure: hexagonal phase h - Yb0.95Sr0.05MnO3 (space group P63cm), orthorhombic phase o - Yb0.69Sr0.31MnO3 (space group Pbnm), hexagonal phase SrMnO3 (space group P63cm). This fact was proved by the ESR measurements in which a several signals due to the phases of different structure were observed. NPD measurements showed that the magnetic structure of h - Yb0.95Sr0.05MnO3 phase is similar to the magnetic structure of the pure h - YbMnO3 and demonstrate the presence of the antiferromagnetic ordering in the samples. ESR and magnetization measurements of h - YbMnO3 sample proved the presence of the antiferromagnetic correlations and also they showed the appearance of the ferromagnetically correlated nanoregions.

The iron(III) compound of composition [Fe(III)(salen)(2-Me-Him)]n, where H2salen = N, N′-ethylenebis(salicylaldimine) and 2-Me-Him = 2-methylimidazolate bridging ligand, was prepared. Magnetic resonance and magnetic susceptibility measurements showed the existence of linear and zigzag antiferromagnetic chains in the compound. Weak ferromagnetism was shown to arise in zigzag antiferromagnetic chains due to antisymmetric exchange interactions. The features of the temperature dependence of magnetization indicate that the magnetic system experiences the transition to the spin-glass state at a temperature below 30 K.

0.85La0.7Sr0.3MnO3/0.15GeO2composite material and pure La0.7Sr0.3MnO3were investigated by X-ray diffraction, scanning electron microscopy, magnetometry and magnetic resonance methods. It was observed that both samples demonstrate the ferromagnetic properties, while the absolute value of the magnetization, the magnetic entropy change and the magnetic ordering temperature decrease in composite in comparison with pure La0.7Sr0.3MnO3. The magnetic resonance spectra of investigated (1-x)La0.7Sr0.3MnO3/xGeO2(x=0, 0.15) can be attributed to the superposition of magnetic resonance spectra from magnetically anisotropic particles with different orientations.

Binary nanoparticles, composed of two different metals, attract significant attention because they possess properties not typical for their respective single-component nanoparticles. In the bulk form, iron and nickel form an alloy called invar in which the two metals are mixed in a ratio of Fe : Ni = 2 : 1. In this work, we demonstrate the formation of alloyed nanoparticles of invar, as opposed to the theoretically possible formation of particles from the two individual metals. The formation of the alloyed nanoparticles is conducted in a two-step process: liquid phase impregnation of graphene oxide with the salts of the metals, and subsequent annealing of the as-formed dry composite. Unlike the solution phase reaction conditions, in this approach, the binary nanoparticles are assembled under conditions where the metal atoms are immobilized on the surface of the decomposing graphene oxide, and at temperatures significantly lower than the melting points of the two metals. The structure of the as-grown nanocrystals is investigated by Mossbauer spectroscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The majority of the Fe/Ni nanoparticles are in a magnetically ordered state, and the composite is a soft magnet.

Electron paramagnetic resonance (EPR) study of the impurity Gd3+ ions in the multi-site SrY2O4 crystal isostructural to the magnetically-frustrated SrGd2O4 compound is reported. Analysis of the angular dependences of the EPR spectra at room temperature allowed us to establish the spin-level energy patterns in the ground states of the Gd3+ ions at the Y(1) and Y(2) sites. Parameters of the spin-Hamiltonian in the frames related to the crystal axes and to the principal center axes are determined.

(1 − x) La 0.7 Sr 0.3 MnO 3 /xNaF (x = 0.05, 0.15, 0.2) composites were synthesized by the conventional solid-state synthesis route, while the sodium fluoride NaF was added to the stoichiometric amount of La 2 O 3 , SrC O 3 and Mn 2 O 3 , that allowed to reduce the synthesis temperature of composites in respect to the pure lanthanum strontium manganite. The phase purity and microstructures of composites were analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Magnetocaloric effect was investigated by means of field dependence magnetization measurements. The significant affect of the additive NaF to the final size and morphology of (1 − x) La 0.7 Sr 0.3 MnO 3 /xNaF composite samples was observed. Though the high-concentration samples (x = 0.15, 0.2) exhibit the lower magnetic entropy changes Δ S M in respect to the pure La 0.7 Sr 0.3 MnO 3 , the expanded temperature dependence of Δ S M curves leads to the slightly higher values of the relative cooling power.

A new cobalt nanoparticles (CoNP) with a core-shell structure were obtained in a matrix of a second generation hyperbranched polyester polyol (BH20). The influence of the molar ratio Co2+ to a BH20 on the nature of stabilization centers of cobalt nanoclusters in the polymer morphology magnetic properties anti-protease activity and hemolytic activity of nanoparticles was studied. The obtained nanoparticles are superparamagnetic and have a blocking temperature of 305 K. Inhibition of the activity of the secretory aspartic protease Candida albicans in the presence of nanoparticles is 58-91%. The hemolytic activity of nanoparticles does not exceed 5%. The data obtained determine the presented cobalt nanoparticles in the matrix of the hyperbranched polyester polyol as a promising nanomaterial with low cytotoxicity for use in medicine and pharmacy.

We present an extensive study of the structural, magnetic and thermodynamic properties of high-quality monocrystals of two heterometallic oxyborates from the ludwigite family: Cu2GaBO5 and Cu2AlBO5 in the temperature range above 2 K. The distinctive feature of the investigated structures is the selective distribution of Cu and Ga/Al cations. The unit cell of Cu2GaBO5 and Cu2AlBO5 contains four nonequivalent crystallographic sites of metal ions. Two sites in the structure of Cu2GaBO5 are fully occupied by Cu atoms which form the quasi one-dimensional chains along the a-axis. For Cu2AlBO5 all sites are partially occupied by Al and Cu atoms. The joint analysis of low-temperature data on magnetic susceptibility and magnetic contribution to the specific heat showed that Cu2AlBO5 and Cu2GaBO5 exhibit an antiferromagnetic transition at T N = 2.4 and 4.1 K, respectively. The magnetic response below T N can be represented as the sum of two contributions: the ordered component and the paramagnetic contribution from defects of the same relative weight. It is shown that the external magnetic field above 2.5 T and 2.8 T for Cu2GaBO5 and Cu2AlBO5, respectively, leads to a broadening of the magnetic phase transition indicating suppression of the long-range antiferromagnetic order.

The incidence of topology on the band structure and physical properties of layered compounds has been extensively studied in semimetals. How those evolve in the presence of electronic correlations has been less investigated so far. In the sodium cobaltates $\mathrm{N}{\mathrm{a}}_{x}\mathrm{Co}{\mathrm{O}}_{2}$ considered here, unexpected magnetic properties associated with correlations on the Co sites were disclosed about 15 years ago. It has also been found that various orderings of the Na atoms occur in between the $\mathrm{Co}{\mathrm{O}}_{2}$ layers in the stable phases of these cobaltates. The distinct Na orders of these phases have been shown to induce specific Co charge disproportionation with large-size unit cells in the $\mathrm{Co}{\mathrm{O}}_{2}$ planes, linked with the diverse magnetic behaviors. This provides an original playground in the studies of interplays between topology and correlations in these layered materials. We present here transport measurements on a series of single crystals and demonstrate that we do synthetize pure phases with quite reproducible transport properties. We show that above room temperature those display a similar behavior whatever the Na content. On the contrary, we provide evidence for a great diversity in Hall effect low-temperature dependences which underscores the specificities of the Fermi-surface reconstructions induced by the Na order. We study in some detail the difference between two metallic phases, one $(x=0.77)$ antiferromagnetic below ${T}_{N}=22\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and the second $(x=2/3)$ paramagnetic down to $T=0$. Both show a sign change in the Hall effect with decreasing $T$. We demonstrate that this can be attributed to quite distinct physical effects. For the $x=0.77$ phase the negative Hall effect has a nonlinear field dependence and occurs in similar conditions to the anomalous Hall effect found in various magnetic metals. In the $x=2/3$ phase in which the Co sites are disproportionated in a kagome substructure, the negative sign of the Hall effect and its two-step $T$ variation have to be assigned to specificities of its Fermi surface. In both cases the anomalies detected in the Hall effect are certainly associated with the topology of their Co electronic bands.

The results of studies of Y$_{2}$Ti$_2$O$_7$ single crystals doped with Er$^{3+}$ and Yb$^{3+}$ ions by means of electron paramagnetic resonance (EPR) and dc-magnetometry are reported. EPR signals of the trigonal centers with the characteristic hyperfine structure of Er$^{3+}$ or Yb$^{3+}$ ions were observed. Field dependences of magnetization of single crystals for magnetic fields directed along the crystallographic axes and temperature dependences of magnetic susceptibilities were measured. Spin Hamiltonian parameters ($g$-factors and parameters of the hyperfine interaction) for Er$^{3+}$ and Yb$^{3+}$ ions were obtained from analysis of experimental data. The registered EPR spectra and magnetization curves were successfully reproduced by simulations in framework of the crystal-field approach, in particular, with an account for hybridization of ground 4f$^{13}$ configuration of Yb$^{3+}$ ions with the charge transfer states., 12 pages, 4 figures, 2 tables

Room-temperature “ferromagnetism” found last decades in nonmagnetic nanoparticles is a puzzle that is not solved yet. In this work we report about the observation of room-temperature magnetism in powders of CaF2 doped with CeO2 as well as in the undoped powder but containing small amount impurity. The studied powders were obtained by grinding of bulk crystals using a sapphire mortar with a pestle. Magnetization dependences on magnetic field for the studied powder samples resemble the dependences observed in nonmagnetic oxide nanoparticles like CeO2. The comparative study of bulk and powder fluorite samples unambiguously confirms the key role of surface defects in the observed features. XRD and TEM measurements show that powder samples have particles of different sizes from the micro down to the submicron scale. The undoped bulk fluorite as well as doped with 0.5at.% (two differently grown crystals), 2at.%, 10at.% of CeO2 revealed only diamagnetic or paramagnetic contribution to magnetization curve whereas the powders of the same samples have ferromagnetic-like contribution on M−H curve. This work may help to get new insight in room-temperature “ferromagnetism” phenomenon of nonmagnetic nanoparticles.

X-band EPR spectra on SiCN ceramics, doped with Fe(III) ions, annealed at 800 °C, 1000 °C, 1100 °C, 1285 °C, and 1400 °C have been simulated to understand better their magnetic properties, accompanied by new magnetization measurements in the temperature range of 5–400 K for zero-field cooling (ZFC) and field cooling (FC) at 100C. The EPR spectra reveal the presence of several kinds of Fe-containing nanoparticles with different magnetic properties. The maxima of the temperature variation of ZFC magnetization were exploited to estimate (i) the blocking temperature, which decreased with annealing temperature of the samples and (ii) the distribution of the size of Fe-containing nanoparticles in the various samples, which was found to become more uniform with increasing annealing temperature, implying that more homogenous magnetic SiCN/Fe composites can be fabricated by annealing at even higher temperatures than 1400 °C to be used as sensors. The hysteresis curves showed different behaviors above (superparamagnetic), below (ferromagnetic), and about (butterfly shape) the respective average blocking temperatures, 〈TB〉. An analysis of the coercive field dependence upon temperature reveals that it follows Stoner–Wohlfarth model for the SiCN/Fe samples annealed above 1100 °C, from which the blocking temperatures was also deduced.

(SrFe 12 O 19 ) x (CaCu 3 Ti 4 O 12 ) 1- x (x = 0.01, 0.03, 0.07, 0.1) composites were synthesized using a solid state method, while the pre-synthesized strontium hexaferrite SrFe 12 O 19 (SFO) was added to the stoichiometric amount of CaO, CuO and TiO oxides to form the CaCu 3 Ti 4 O 12 (CCTO) structure around SFO microinclusions. The structural and microstructural properties of obtained composites were studied by X-ray diffraction, scanning electron microscopy and transmission electron microscopy techniques. The magnetic properties were studied by electron spin resonance and magnetometry methods. Based on all experimental data we can conclude, that SFO x CCTO 1- x nanostructured composites were formed only for concentrations x = 0.03 and x = 0.07, where SFO nanoinclusions are inside CCTO matrix, that leads to the strong mutual influence of the magnetic properties of both component.

The trapped magnetic flux in the finely ground pyrolytic graphite sample annealed at 670 K in air has been observed. Flux trapping occurs on cooling of the sample from room temperature to 10 K in a magnetic field of 1 T. The magnitude and sign of the induced trapped moment remain unchanged when the applied magnetic field is varied within ±1 T at T K. The trapped magnetic flux is manifested in the displacement of the magnetization curve relative to that of the sample cooled in zero field. Displacement magnitude gradually decreases with the temperature increase up to 350 K, not reaching zero. The set of experimental observations probably reflects the presence in the sample of a granular high-temperature superconducting phase.

The first paramagnetic pentagonal-bipyramidal complex of Mo(III) with a N3O2-type Schiff-base ligand was synthesized by the comproportionation reaction between Mo(II) and Mo(IV) congeners. The complex has a low-spin (S = 1/2) ground state of MoIII(4d3) with double orbital degeneracy and unquenched orbital momentum, which result in strong Ising-type magnetic anisotropy.

Membrane-electrode assemblies (MEA) with a cathode catalyst made of a nickel sodium pectate complex PG-NaNi with a 25% substitution of sodium for nickel, and with a commercial anode catalyst made of platinum black have been successfully created. Tests in a H2/O2 proton exchange membrane fuel cell (PEMFC) yielded the values of the maximum current density of 59 mA cm−2 and the maximum power density of 5.9 mW cm−2. These results permit the development of environmentally friendly and stable cathode catalysts for PEMFCs made of a readily available biological raw material, pectin.

The temperature dependences of the magnetic susceptibility in magnetic fields applied parallel and perpendicular to axis с of a Mn0.89Mg1.11BO4 single crystal were measured. Spin ordering typical of an antiferromagnetic with an easy magnetization axis was observed below 16 K. The Dzyaloshinskii–Moriya interaction between spins of manganese ions in Mn0.89Mg1.11BO4 was estimated by analyzing the EPR linewidth.

Single crystals of Cu2AlBO5 and Cu2GaBO5 copper oxyborates are synthesized via solution-melt crystallization and subjected to X-ray diffraction analysis. Parameters of the crystal lattice and the positions of atoms in a unit cell are determined. Copper ions form a structural chain along axis а in Cu2AlBO5 and Cu2GaBO5. Temperature dependences of the magnetic susceptibility are measured. The obtained curves feature kinks at Т = 2.4 (Cu2AlBO5) and 4.1 K (Cu2GaBO5).

Magnetic properties of a new single crystal MnMgBO4 have been studied. It was determined that below 16 K antiferromagnet spin order was observed with the axis of easy magnetization along the c axis crystal. The short antiferromagnetic range order was observed below 100 K. The Curie–Weiss temperature has been determined in single crystal MnMgBO4 as θCW = −98 K and the frustration parameter has been estimated as 6.125.

A series of seven-coordinate pentagonal-bipyramidal (PBP) Cr(III) complexes with pentadentate pyridine-based ligands, 2,6-diacetylpyridine bis(4-methoxybenzoylhydrazone), H2DAPMBH (H2LOCH3) or 2,6-diacetylpyridine bis(benzoylhydrazone), H2DAPBH (H2L) and different axial ligands have been prepared. The reaction of the H2LOCH3 with CrCl2·4H2O in methanol or CrCl3·6H2O in CH3CN led to a novel seven-coordinate pentagonal-bipyramidal (PBP) complex [Cr(HLOCH3)Cl2] (1) with the mono-deprotonated chelating ligand in the equatorial plane and two apical Cl atoms. Then, taking advantage of lability of the apical Cl ligands in 1, a number of PBP CrIII complexes with charged (viz. CH3O−, N3−, CN−, NCS−) and neutral (viz. CH3OH, H2O) apical ligands was obtained and characterized: [Cr(HLOCH3)Cl2]·4CHCl3 (1), [Cr(HLOCH3)Cl2]·CH3OH (1a), [Cr(HLOCH3)(H2O)Cl]PF6·CH3OH (2), [Cr(HL)(H2O)Cl]ClO4·0.25H2O (3), [Cr(HLOCH3)(H2O)2](NO3)2·H2O·C2H5OH (4), [Cr(LOCH3)(CH3OH)(OCH3)]·CH3OH (5), [Cr(HLOCH3)(NCS)2]·1.5H2O (6), [Cr(HLOCH3)(N3)2]·xH2O (7, x = 0.2, 8, x = 0, 9, x = 0, three phases in the same synthesis), [Cr(LOCH3)(N3)2][Na(CH3OH)2]·2CH3OH (10), [Cr(LOCH3)(CN)2][Na(H2O)(C2H5OH)] (11). Single crystal X-ray analysis reveals that all the complexes 1–11 have the PBP geometry with a pentadentate ligand in a form of [HLOCH3]− or [LOCH3]2− in the equatorial plane. The PBP complexes are prone to aggregate into dimers or polymers, either due to strong hydrogen bonds or due to the transformation of terminal ligands into bridging between different metallic centers. All complexes 1–11 exhibit considerable in-plane distortion of the CrN3O2 pentagon due to the shift of the CrIII ion from the central position, which is caused by the strong first-order Jahn-Teller (JT) effect for the high-spin 3d3 configuration in the PBP ligand field. The mechanism of JT distortions is rationalized in terms of DFT calculations. DC magnetic measurements indicate a high-spin (S = 3/2) ground state of complex [Cr(HLOCH3)Cl2]·4CHCl3 (1); theoretical analysis of its magnetic properties reveals negative zero-field splitting energy with the anisotropy parameter D = –1.8 cm−1 and weak dimer-like antiferromagnetic spin coupling J = –0.23 cm−1 between neighboring PBP units [CrIII(HLOCH3)Cl2] mediated by π-stacking of planar H2LOCH3 ligands.

(La0.7Sr0.3MnO3)x(CaCu3Ti4O12)1−x (0.01 ≤ x ≤ 0.3) nanostructured composites with La0.7Sr0.3MnO3 (LSMO) microinclusions in CaCu3Ti4O12 (CCTO) matrix were synthesized using a solid state method. The structural and microstructural details were studied by X-ray diffraction (XRD), X-ray fluorescence (XFA), scaning electron microscope (SEM) and transmission electron microscope (TEM) techniques. The magnetic properties were studied by electron spin resonance (ESR) and magnetometry methods. In the concentration range 0.01

Compounds [Fe(3-MeO-Qsal)2]Y (Y = PF6, BF4) have been prepared by diffusion method and studied in temperature range 5–300 K by EPR and magnetic susceptibility methods. The coexistence of spatially separated high-spin (solvated) and low-spin (unsolvated) fractions in the studied compounds has been established. It has been shown that change in the type of outer-sphere anion leads to change in the character of intermolecular interactions in the high-spin fraction and has no effect on the parameters and character of interactions of paramagnetic centers in the low-spin fraction.

A series of five new mononuclear pentagonal bipyramidal Co(II) complexes with the equatorial 2,6-diacetylpyridine bis(semicarbazone) ligand (H2dapsc) and various axial pseudohalide ligands (SCN, SeCN, N(CN)2, C(CN)3, and N3) was prepared and structurally characterizated: [Co(H2dapsc)(SCN)2]∙0.5C2H5OH (1), [Co(H2dapsc)(SeCN)2]∙0.5C2H5OH (2), [Co(H2dapsc)(N(CN)2)2]∙2H2O (3), [Co(H2dapsc)(C(CN)3)(H2O)](NO3)∙1.16H2O (4), and {[Co(H2dapsc)(H2O)(N3)][Co(H2dapsc)(N3)2]}N3∙4H2O (5). The combined analyses of the experimental DС and AC magnetic data of the complexes (1&ndash, 5) and two other earlier described those of this family [Co(H2dapsc)(H2O)2)](NO3)2∙2H2O (6) and [Co(H2dapsc)(Cl)(H2O)]Cl∙2H2O (7), their theoretical description and the ab initio CASSCF/NEVPT2 calculations reveal large easy-plane magnetic anisotropies for all complexes (D = + 35 &minus, 40 cm‒1). All complexes under consideration demonstrate slow magnetic relaxation with dominant Raman and direct spin&ndash, phonon processes at static magnetic field and so they belong to the class of field-induced single-ion magnets (SIMs).

Novel heteroleptic Er(iii) and Yb(iii) naphthalocyaninato-phthalocyaninates containing an octa-phenyl or octa-phenoxysubstituted naphthalocyanine deck were synthesised and identified by 1H NMR, EPR and high resolution MALDI-TOF/TOF mass spectrometry. Direct synthesis of novel homoleptic Yb(iii) bis (octa-phenylnaphthalocyaninate) was carried out. Downfield lanthanide induced shifts of the aromatic protons in target compounds were observed compared with the corresponding diamagnetic Lu(iii) complexes. In the near-IR absorption spectra, an increase in ionic radius from Lu(iii) to Er(iii) resulted in a bathochromic shift of the intervalence band up to 1473 nm. This work presents the first experimental EPR study of Yb(iii) bis naphthalocyaninate, where a set of magnetic parameters and properties (including spin, magnitude and sign of magnetic anisotropy parameter D, increased splitting in a crystal field, ferromagnetic f-π interaction etc.) were determined and interpreted by both EPR and SQUID techniques and supported by theoretical considerations.

New nickel-based complexes of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-bian) with BF4 - counterion or halide co-ligands were synthesized in THF and MeCN. The nickel(I) complexes were obtained by using two approaches: 1) electrochemical reduction of the corresponding nickel(II) precursors; and 2) a chemical comproportionation reaction. The structural features and redox properties of these complexes were investigated by using single-crystal X-ray diffraction (XRD), cyclic voltammetry (CV), and electron paramagnetic resonance (EPR) and UV/Vis spectroscopy. The influence of temperature and solvent on the structure of the nickel(I) complexes was studied in detail, and an uncommon reversible solvent-induced monomer/dimer transformation was observed. In the case of the fluoride complex, the unpaired electron was found to be localized on the dpp-bian ligand, whereas all of the other nickel complexes contained neutral dpp-bian moieties.

Needle-shape single crystals of Mn2.25Co0.75BO5 ludwigite were synthesized by the flux technique and investigated by means of X-ray diffraction, static magnetic susceptibility and specific heat measurements. Magnetization and specific heat experiments showed the presence of ferrimagnetic ordering near T N ≃ 61 K. Below this temperature the magnetic properties demonstrated the angular dependence and the high magnetic hardness in a magnetic field applied perpendicular to the crystallographic c axis, which is similar to other cobalt-containing ludwigites. The effective magnetic moment per magnetic ion 4 . 8 μ B was calculated from the paramagnetic data. Analysis of the phonon contribution to the specific heat allowed to distinguish the magnetic contribution C M , which has two features. One of which was observed at T N and can be attributed to strong exchange interactions between spins of magnetic ions. The second one at T = 11.6 K is due to the effect of the ligands crystal field on a magnetic ion with S > 1 ∕ 2 .

s This study is devoted to the investigation of the high dielectric constant causes in complex oxides with a structure of the K2NiF4 type. А new thermobaric treated ceramics on the basis conjugate LaxSr2-xFeхTi1-хO4 (х ​= ​0.5, 0.7) solid solutions was synthesized and the study their structure, microstructure, magnetic and dielectric properties was performed. It is shown that antiferromagnetic interactions coexist with ferromagnetic, which become dominant towards to low temperatures; the appearance of two types of magnetic interactions may be related to the presence of magnetic ions of different valences. Different values of the dielectric constants e are observed in wide region of frequencies 10–107 ​Hz. In obtained at ambient pressure LaxSr2-xFeхTi1-хO4 (х ​= ​0.5, 0.7) ceramics the highest permittivity e value is only 30–50 in the frequency range from 1 ​kHz to 1 ​MHz. After the samples treatment at 1273 ​K and P ​= ​4 ​GPa during 5 ​min e increases to 5–102–103 ​at 293 ​К and independent of frequency in the range (102–106) Hz. At the temperature increase the permittivity as well increases and the e value becomes ~106 at, approximately, f ​= ​100 ​Hz and T ​= ​750 ​K. An obvious change of samples microstructure and polyhedra structure anisotropy in LaxSr2-xFeхTi1-хO4 (х ​= ​0.5, 0.7) was observed after the thermobaric treatment. Described in this article performed dielectric properties investigations indicate that possible reasons of the high-permittivity origin are specifics of layered structure, microstructure and charge polarization associated with it, Maxwell-Wagner polarization at the grain boundaries and inhomogeneities and small polaron hopping conduction mechanism.

[FeLX2]Y [L = N,N'-ethylenebis(salicylimine) (salen), N,N'-ethylenebis(acetylacetonylimine) (acen), or N,N'-ethylenebis(3-methyloxysalicylimine) (vanen); X = imidazole or N-methylimidazole; Y = BF4, ClO4, or BPh4] compounds have been prepared and studied by means of EPR and magnetic susceptibility measurements at 5–300 K. It has been shown that the different electron-donating properties of acen and salen planar ligands result in different spin states of Fe(III) ions. Intermolecular π-interactions of the outer-sphere BPh4 ion affect the complexes spin state as well.

New composite materials (SrFe12O19)x(CaCu3Ti4O12)1–x (x = 0, 0.05, 1) have been synthesized. Their magnetic properties are studied in the temperature range 5–300 K using the magnetic resonance and magnetometry methods. It is found that strontium hexaferrite microinclusions in the (SrFe12O19)0.05(CaCu3Ti4O12)0.95 composite “magnetize” CaCu3Ti4O12 at temperatures from 300 to 200 K, forming a ferrimagnetic particle near the SrFe12O19 “core.” The magnetic resonance line below 200 K splits into two lines corresponding to SrFe12O19 and CaCu3Ti4O12. The core effect decoration is manifested in the increase in the Curie–Weiss temperature from 25 K in CaCu3Ti4O12 without the doping ceramics to 80 K in the composite with 5% of SrFe12O19.

The [Fe(acen)pic2]BPh4 · nH2O compound has been synthesized and studied in the temperature interval of 5–300 K by the methods of EPR and magnetic susceptibility. The existence of ferromagnetic interactions between Fe(III) complexes in this compound has been revealed, in contrast to unhydrated [Fe(acen)pic2]BPh4. The reduction in the integrated intensity of the magnetic resonance signal as the temperature decreases below 80 K has been explained by the transition of high-spin ions to the low-spin state. It has been shown that the phase transition temperature in the presence of intermolecular (ferromagnetic) interactions is lower than that in the case of noninteracting centers.

The EPR spectrum of Mn-doped lanthanum gallate single crystals grown by floating zone melting with optical heating has been studied. In contrast to the crystals grown according to the Czochralski method, no manganese is found in these crystals even after high-temperature annealing in air. The spectral characteristics of Fe3+ and Gd3+ centers in crystals prepared by various methods have been compared in the rhombohedral phase, and the fourth-rank nondiagonal parameters of the Fe3+ trigonal centers have been determined, as well.

The results of growth of two oxyborate single crystals, Cu2GaBO5 and Cu2AlBO5, with ludwigite structure from different flux systems using the spontaneous nucleation technique are reported. We obtained large Cu2GaBO5 and Cu2AlBO5 crystals of dimensions up to 3 × 4 × 15 mm3 and 1 × 1 × 10 mm3, respectively. Trimolybdate-bismuth fluxes diluted with the sodium carbonate for both Cu2GaBO5 and Cu2AlBO5, as well as lithium-molybdate and lithium-borate fluxes for Cu2AlBO5, were used. It was observed that the growth of Cu2GaBO5 and Cu2AlBO5 is accompanied by the growth of CuO, Cu2Al6B4O17, and Cu2Al1-xGaxBO5 crystals as secondary phases. Structural and magnetic characterization of the crystals is also performed.

We present the results of the investigations of high conducting area and superconductivity at the interfaces between ferroelectric oxide and insulating oxide in heterostructures, isostructural to BaTiO3/La2CuO4. The performed numerical simulations of BaTiO3/La2CuO4 heterostructure show the possibility of high conductivity state at the interface. The temperature dependence of the measured electrical resistance of the Ba0.8Sr0.2TiO3/La2CuO4 heterostructure interface have been studied and the superconducting behaviour with transition temperature Tc about 30K has been found. Therefore, the transition to the state with 2DEG at the interface is demonstrated. The results offer the possibility to design novel electronic devices.

In this study, we synthesized single crystals of Na$_{x}$CoO$_{2}$ with $x\sim0.8$ using the optical floating zone technique. A thorough electrochemical treatment of the samples permitted us to control the de-intercalation of Na to obtain single crystal samples of stable Na ordered phases with $x=0.5-0.8$. Comparisons of the bulk magnetic properties with those observed in the Na ordered powder samples confirmed the high quality of these single crystal phases. The ab plane resistivity was measured for the Na ordered samples and it was quite reproducible for different sample batches. The data were analogous to those found in previous initial experimental studies on single crystals, but the lower residual resistivity and sharper anti-ferromagnetic transitions determined for our samples confirmed their higher quality., Comment: 15 pages, 7 figures

A series of cobalt (Co) and its oxides based nanoparticles were synthesized by using hyperbranched polyester polyol Boltorn H20 as a platform and sodium borohydride as a reducing agent. UV, FT-IR, XRD, NTA, and TEM methods were employed to obtain physicochemical characteristics of the products. The average diameter of Co nanoparticles was approximately8.2±3.4 nm. Their magnetic properties, including hysteresis loop, field-cooled, and zero field-cooled curves were investigated. The nanoparticles exhibit superparamagnetism at room temperature, accompanied by magnetic hysteresis below the blocking temperature.

Single crystals of sodium cobaltates Na$_{x}$CoO$_{2}$ with $x \approx 0.8$ were grown by the floating zone technique. Using electrochemical Na de-intercalation method we reduced the sodium content in the as-grown crystals down to pure phase with 22 K N\'eel temperature and $x \approx 0.77$. The $^{59}$Co NMR study in the paramagnetic state of the $T_{N}=22$ K phase permitted us to evidence that at least 6 Co sites are differentiated. They could be separated by their magnetic behaviour into three types: a single site with cobalt close to non-magnetic Co$^{3+}$, two sites with the most magnetic cobalts in the system, and the remaining three sites displaying an intermediate behaviour. This unusual magnetic differentiation calls for more detailed NMR experiments on our well characterized samples., Comment: 5 pages, 4 figures, submitted to JETP Lett

Here we report the magnetic susceptibility measurements of magnetron sputtered orthorhombic manganite RMnO 3 (R=Yb, Gd) thin films deposited on dielectric LaAlO 3 and ferroelectric SrTiO 3 , LiNbO 3 substrates. We observed that all of investigated o-RMnO 3 films show a splitting in the temperature dependence of ZFC and FC magnetization curves. We found that the substrate can impact on the splitting temperature ZFC-FC curves and absolute value of the magnetization of thin films.

The objects of the investigation were uniformly Ag+ doped Hg0.76Cd0.24Te mercury chalcogenide monocrystals obtained by ion implantation with subsequent thermal annealing over 20 days. After implantation and annealing the conductivity was inverted from n-type with carrier concentration of 1016 cm−3 to p-type with carrier concentration of ≈ 3.9 × 1015 cm−3. The investigations of microwave absorption derivative (dP/dH) showed the existence of strong oscillations in the magnetic field for Ag:Hg0.76Cd0.24Te in the temperature range 4.2–12 K. The concentration and effective mass of charge carrier were determined from oscillation period and temperature dependency of oscillation amplitude. We suppose that this phenomenon is similar to the de Haas–van Alphen effect in weakly correlated electron system with imperfect nesting vector.

${\mathrm{SrEr}}_{2}{\mathrm{O}}_{4}$ is a geometrically frustrated magnet which demonstrates rather unusual properties at low temperatures including a coexistence of long- and short-range magnetic order, characterized by two different propagation vectors. In the present work, the effects of crystal fields (CFs) in this compound containing four magnetically inequivalent erbium sublattices are investigated experimentally and theoretically. We combine the measurements of the CF levels of the ${\mathrm{Er}}^{3+}$ ions made on a powder sample of ${\mathrm{SrEr}}_{2}{\mathrm{O}}_{4}$ using neutron spectroscopy with site-selective optical and electron paramagnetic resonance measurements performed on single-crystal samples of the lightly Er-doped nonmagnetic analog, ${\mathrm{SrY}}_{2}{\mathrm{O}}_{4}$. Two sets of CF parameters corresponding to the ${\mathrm{Er}}^{3+}$ ions at the crystallographically inequivalent lattice sites are derived which fit all the available experimental data well, including the magnetization and dc susceptibility data for both lightly doped and concentrated samples.

Here we present the investigation of the orthorhombic o-LuFeO3 thin film grown on SrTiO3 (001) substrate. Temperature dependencies of magnetization measured in magnetic fields 1000 Oe and 2000 Oe were described in the assumption that ferromagnetic correlated regions are presented in samples together with the paramagnetic phase. Additional argument in favor of the ferromagnetic regions existence in o-LuFeO3 is the magnetic hysteresis curve measured at T=5 and 100K. The temperature dependences of dielectric response were measured and analyzed.

We present the results of magnetic and Mossbauer effect studies of zinc oxide thin film obtained by RF magnetron sputtering and implanted with 40 keV iron ions to a fluence of 1.51017 ion/cm2. As-implanted and post-annealed sample shows ferromagnetic properties at room temperature and consists of paramagnetic and ferromagnetic phases according to Mossbauer spectroscopy.