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The dielectric and magnetic properties of ceramics based on barium titanate and solid solutions of barium strontium titanate doped with iron and gadolinium ions at concentrations below 5 mol.% have...

The magnetic and magnetotransport properties of thin Heusler alloy Ni49.7Fe17.4Co4.2Ga28.7 films deposited onto MgO(100) substrates are studied over a wide temperature range, which includes a martensitic transition (MT). For this composition, the MT is not accompanied by a magnetic phase transition, since the martensitic and austenitic phases are ferromagnets with similar magnetizations. The electrical resistivity does not undergo sharp changes during the MT. The magnetoresistance is negative, decreases in magnitude with increasing temperature in the range 100–250 K corresponding to the MT, and then increases to –1%. The field dependences of the Hall effect resistivity have the shape that is characteristic of homogeneous ferromagnetic alloys. The coefficients of the normal and anomalous Hall effects are determined. The anomalous Hall effect coefficient is shown to be described by the relation Rs = αρ + βρ2, where ρ is the electrical resistivity and the second term is lower than the first, which indicates an important role of the interference impurity–phonon scattering mechanism.

β-NaYF4:Eu3+ microparticles co-doped with Gd3+ ions were obtained by hydrothermal synthesis at 180 °C using citric acid as a stabilizing agent. All synthesized materials have a β-NaYF4 crystalline phase, where the unit cell volume increases upon the addition of Eu3+ and Gd3+ ions. The particles have a hexagonal prism shape and a size of 40–714 nm, where Eu3+ and Gd3+ doping results in size reduction. Upon 393 nm excitation, phosphors exhibit distinct emission peaks centered at 591, 615, and 695 nm and a weak band at 650 nm attributed to 5D0–7FJ transitions (J = 1–4). The optimum Eu3+ doping concentration was found to be 30% in the NaYF4 host. Concentration quenching was realized through dipole–dipole interactions. Kinetic measurements showed a gradual decline of the 5D0 lifetime from 6.7 ms to 2.2 ms along with an increase in Eu3+ doping concentration. Co-doping of the small Gd3+ number led to an increase of emission intensity and 5D0 lifetime. The effects of Eu3+ doping and Gd3+ co-doping on radiative and nonradiative decay rates were studied using 4f–4f intensity theory.

We present results of magneto-optical investigations of (CoFeB) x -(Al-O)100- x film nanocomposites in transverse Kerr effect (TKE) geometry in the spectral range 0.5–4.0 eV and magnetic field up to 3.1 kOe. Nanocomposites were deposited onto a glass-ceramic substrate by ion-beam sputtering. According to the data obtained from resistivity measurements, the percolation threshold is about x per a 57 at.%, and the critical concentration for metal–insulator transition is about x c a 48 at.%. The TKE response at room temperature strongly depends on the wavelength of light, applied magnetic field H , and the volume metallic fraction. The TKE field dependence is almost linear to H = 3.1 kOe and identical for 1.57 and 3.06 eV at x ≤ 30 at.%. It means that at x ≤ 30 at.%, nanocomposites consist of only superparamagnetic granules. With increasing concentration x , the TKE field dependence at 3.06 eV becomes more and more similar to the field dependence of ferromagnetic material, but it is not the case at 1.57 eV. For example, the TKE signal for x = 43 at.% measured at 3.06 eV saturates at H = 100 Oe, which indicates the presence of large ferromagnetic regions below x c. For the same composition, the TKE field dependence measured at 1.57 eV does not saturate and resembles more a superparamagnetic response. The same difference is observed also at x = 49 at.%. The presence of large ferromagnetic regions in completely insulating samples together with separate superparamagnetic granules can be considered as an evidence of superferromagnetic ordering in the vicinity of x c.

Magnetic Heusler alloys X2BZ (where X and B are 3d elements and Z belongs to the sp group) exhibit diverse magnetic and structural properties, which are important for designing multifunctional smart materials. Electronic band structure calculations demonstrate that, if the valence of element B is higher than that of element X, such alloys (so-called inverse Heusler alloys) can behave differently as compared to traditional Heusler alloys. The growth, the crystal structure, and the magnetic properties of thin films of a new Mn2FeSi Heusler alloy deposited under various conditions (including various substrates and annealing temperatures) are studied in this work. A temperature-induced structural transition into a low-magnetization martensitic phase and a thermally stable austenitic phase are detected. A magnetic field of 500 Oe applied to some samples at a temperature of 380 K is found to cause a large exchange bias (about 1 kOe) at T = 10 K. The influence of the type of substrate and the annealing temperature on the magnetic and structural properties of the films is discussed.

Accurate thermal sensing with good spatial resolution is currently required in a variety of scientific and technological areas. Luminescence nanothermometry has shown competitive superiority in contactless temperature sensing, especially at the nanoscale. To broaden the use of such thermometers, development of a novel sensor type with high sensitivity and resolution is highly demanded. Herein, we report single-phase Ln3+-doped YVO4 nanophosphors synthesized using a modified Pechini method as multimode optical thermometers for wide-range temperature probing (299–466 K). The observed temperature-induced red shift of the charge transfer band was utilized to provide thermal sensing. Temperature sensing was based on the luminescence intensity ratio using emission intensities obtained upon charge transfer and direct lanthanide excitation, the spectral position of the charge transfer band and its bandwidth. The suggested probing strategies provided a high relative thermal sensitivity (up to 3.09% K−1) and a precise temperature resolution (up to 0.1 K). The obtained results can be useful for the design of novel contactless luminescence thermometers.

Functionalized dendrimers are a novel type of dendritic macromolecules that contain functionalized groups that do not take part in the dendrimer’s synthetic cycle. Focusing on the local dynamics of...

For the first time, the 3(X + M)LCT origin of both the lowest excited triplet states of dual-emissive tetranuclear copper(I)-iodide complexes with the octahedral Cu4I4 core has been revealed using quantum chemical computations in contrast to the conventional assignment of the lowest-energy emission to the 3CC state. The unusual thermochromic behavior shown for dual emission from these states of Cu4I4 clusters stabilized by P,N-ligands allows optical ratiometric thermal sensing in a broad temperature range.

Eu3+-doped MgAl2O4 nanoparticles were prepared by modified Pechini method. X-ray diffraction analysis shows pure tetragonal spinel phase without any impurities. The average size of synthesized nanoparticles was determined to be about 50–60 nm using scanning electron microscopy and static light scattering techniques. Emission and excitation spectra as well as lifetimes of MgAl2O4:Eu3+ nanophosphors were explored in surrounding media with different refractive indexes. Surrounding medium does not affect luminescence bands position, whereas 5D0 lifetime monotonically decreases along with increase of medium refractive index. Effect of surrounding media on radiative and nonradiative decay rates, which were calculated using 4f–4f intensity theory, was studied and discussed. Filling factor of prepared nanoparticles is defined using both radiative and observed lifetimes.

Two metamagnetic Heusler alloys based on Ni45Cr5Mn37In13 with differing Mn concentrations (by 0.2 at. %) were studied using magnetization, resistivity, and Hall resistivity measurements. It is shown that this small variation in composition leads to fundamental changes in magnetic properties. Near the martensitic phase transitions, the anomalous Hall coefficient (RS) was found to increase with temperature while the resistivity (ρ) decreases. Thus, in the case of Ni45Cr5Mn37In13, the general correlation between RS and ρ, considered as applicable for all crystalline and amorphous ferromagnetic alloys, breaks down completely. We explain this behavior in the framework of an s-d model where it is assumed that the resistivity and anomalous Hall effect are determined by different groups of current carriers.

We present investigation of microwave permeability of thin supermalloy films deposited on a flexible substrate. The permeability measurements are performed by transmission-reflection technique in a coaxial line under external magnetic bias in the frequency range of 100 MHz–20 GHz. It is shown that demagnetization does not affect the measurements when bias is above 150 Oe. Magnetic characteristics of the films are determined by two approaches: (i) fitting of the resonant frequency dependence on magnetic bias by Kittel's equation and (ii) calculation of the parameters from the Landau–Lifshitz–Gilbert dispersion law. Both approaches give close results for values of magnetoelastic field, anisotropy field, saturation magnetization, and damping factor.

The contactless real-time temperature sensing technique with high temporal and spatial resolution is in high demand for the countless applications. Here, the Yb3+/Er3+−codoped GeO2–PbO–PbF2 glass ceramics synthesized via the melt-quenching technique has been presented as an optical thermometer. The thermal sensing was designed based on the temperature dependent fluorescence intensity ratios of thermally (2H11/2 and 4S3/2) and non-thermally (2H11/2 and 4F9/2) coupled Er3+ levels. The ratiometric techniques provide the thermal sensing within the temperature range of 300–466 K. The absolute and relative thermal sensitivities as well as the temperature resolution were calculated and compared with other Yb3+/Er3+-doped materials. The temperature of the microelectronic component on the printed circuit board was defined using the optical thermometry as a proof of concept revealing Yb3+/Er3+−codoped GeO2–PbO–PbF2 phosphor to be a promising candidate for precise non-contact thermal sensor.

With the aim to analyze the microstructure of the polar nanoregions of mixtures of ionic liquids and inorganic salts and the single particle dynamics of metal cations in these densely ionic environments, solutions of inorganic nitrate salts (lithium, magnesium, calcium and aluminium nitrates) in the protic ionic liquid ethylammonium nitrate have been characterized by means of nuclear magnetic resonance. The measured spectra reveal that, despite being dried under vacuum, all the studied mixtures contained variable amounts of water, but, while in those with the salt cations of lower ionic potentials (Li+, Ca2+) only bulk free water that can be almost completely removed from the mixture is found, mixtures with the cations of higher ionic potentials (Mg2+, Al3+) contain only hydration water structurally anchored in the primary solvation shells of the metal cations forming coordination complexes inside the polar nanoregions of the densely ionic solvent and, thus, non-removable under vacuum. This hydration water is not properly detected by common Karl Fisher methods and these solutions are sometimes mistakenly considered anhydrous. Moreover, our NMR measurements confirm the nanostructured solvation paradigm, since they show that the influence of the addition of salt on the chemical shifts of the signals associated to hydrogen atoms in the apolar regions of the protic ionic liquid is negligible. Single-particle dynamics of cations of low and high ionic potentials was also studied, and our observations for the diffusion coefficients of lithium and aluminium cations support the conclusion that Li+ diffusion takes place inside anhydrous [Li(NO3)4]3− complexes, while kinetic complexes with Al3+ gather around [Al(H2O)6]3+) aqua ions.

Development of new approaches to the noncontact optical thermometry is of great importance for modern science and technology. In the current work, single-phase YVO4:Eu3+ nanoparticles prepared via ...

The adiabatic temperature change (ATad) in Ni 45 Mn 43 CoSn 11 has been measured by a direct method in magnetic field changes up to 14 T. Large reversible magnetocaloric effects resulting in AT ad of about = -11 and 5 K have been observed for magnetic field changes of 14 T at the magnetostructural (T A ~ 260 K) and magnetic transitions (T C ~ 320 K), respectively. The impact of the thermomagnetic history on AT ad at high magnetic fields has been reported. The significant observed changes in the relaxation time of AT ad , depending on the type of the phase transitions, magnetization, and demagnetization cycle are discussed.

We present density functional theory calculations to study the interplay between magnetic and structural properties in Ni-Co-Mn-Sn. The relative stability of austenite (cubic) and martensite (tetragonal) phases depends critically on the magnetic interactions between Mn atoms. While the standard generalized gradient approximation (GGA) stabilizes the latter phase, correlation effects beyond GGA tend to suppress this effect. Mn atoms treated as magnetic impurities can explain our results, where a delicate balance between magnetic interactions mediated by Ni d and Sn p orbitals determines the equilibrium structure of the crystal. Finally, we discuss the role of Co doping in stabilizing ferromagnetic austenite phases.

Due to their well-defined structure, multivalency, biocompatibility, and low toxicity, lysine dendrimers can be used as safe and efficient nanocarriers for drug and gene delivery. One useful strategy for improving the gene delivery properties of dendrimers is modification with arginine amino acid (Arg) residues. Incorporation of Arg residues could be favorable for the enhancement in transfection efficiency of lysine based dendrimers. In this work, we have synthesized a new second-generation poly-L-lysine dendrimer with repeating units containing two linear Arg residues between neighboring lysine branching points (Lys-2Arg dendrimer) and studied its physicochemical properties. We confirmed the structure of Lys-2Arg dendrimer using various one- and two-dimensional 1H and 13C NMR spectroscopy methods. Comparison of T1H relaxation data for Lys-2Arg and Lys-2Lys dendrimers showed that the replacement of double Lys residues with double Arg residues resulted in a sharp decrease in the mobility of methylene groups in side segments and in the main chain of e-Lys inner segments. We suggest that this unexpected effect is caused by a guanidine–guanidine pairing effect in water, which leads to entanglements between dendrimer branches.

A nonlinear spin-wave (magnonic) logic gate based on the ferrite-film Mach-Zehnder interferometer was realized. The gate has two inputs and one output. The principle of operation of the device is based on the power-dependent phase shift of spin waves propagating in an yttrium iron garnet film. A XOR logic functionality for two digital data streams supplied to the gate inputs is shown. No control signal is needed for the gate operation. The performance characteristics of the device are discussed. Reliable functionality in the pulsed regime at 50 and 250 kb/s is demonstrated.

Development of new contactless thermometers with improved characteristics is highly demanded for science and technology. In this work, we present upconverting Tm3+/Yb3+-doped GeO2–PbO–PbF2 glass ceramics as optical temperature sensor. Upon 973 nm laser excitation, sample generates intense emission bands from blue to NIR regions due to ladder-like energy levels of Tm3+ ion. A ratiometric technique involving the Tm3+ thermally and non-thermally coupled levels (1G4(a), 1G4(b), 3F2,3, 3H4) and spectral line position of 3H4–3H6 transition was used to provide thermal sensing in the 300–466 K temperature range. The performance of suggested sensing parameters was compared and discussed in terms of relative thermal sensitivity. The maximal thermal resolution, which can be achieved using Tm3+/Yb3+-doped GeO2–PbO–PbF2 thermometers, is better than 1 K at both 303 and 465 K. The obtained results show the potential use of GeO2–PbO–PbF2: Tm3+,Yb3+ phosphor for optical sub-degree temperature sensing.

Here, we report Nd3+-doped Y2O3 nanoparticles suitable for luminescence thermal sensing in the first and second biological windows. The nanoparticles were synthesized via the combined Pechini-foaming method. A ratiometric approach, based on the relative changes in the intensities of different emission bands corresponding to the Stark sublevels or excited levels, was applied to determine local temperature. The evaluated thermal sensitivities differed 5-fold times depending on the choice of transitions for the luminescence intensity ratio calculation. The temperature uncertainty was determined to be below 1 °C, which allows to perform sub-degree thermal sensing. The results of ex vivo experiment indicate that Nd3+-doped Y2O3 nanoparticles are promising candidates for real biological applications.

In this work we present the study of electrochemical properties of the composites based on cellulose nanofibers and a conductive polypyrrole that can be used as an electrode in supercapacitors. Samples have been prepared by two methods: in situ polymerization of pyrrole in the presence of cellulose nanofibers directly on the graphite plate used as a current collector and by precipitation of the dispersion of polypyrrole-cellulose nanofibers prepared ex situ onto the graphite electrode. Higher specific capacitance up to 4.08 F/cm2 (810 F/g) for in situ prepared sample in comparison with 1.87 F/cm2 (371 F/g) for ex situ sample was measured. Investigation with galvanostatic charge-discharge and electrochemical impedance spectroscopy revealed that the sample prepared by precipitation of dispersion demonstrate higher double-layer capacitance, electrode prepared via in situ polymerization demonstrates higher pseudocapacitance. Analysis of electrochemical data with equivalent circuit allows to propose that deviation from ideal capacitance behavior is caused by chemical inhomogeneity of surface of prepared materials rather than by their porous structure.

It is shown that the transport properties of graphitized silicon carbide are controlled by a surface graphene layer heavily doped with electrons. In weak magnetic fields and at low temperatures, a negative magnetoresistance is observed due to weak localization. A crossover in the magnetoresistance from weak localization to weak antilocalization (the latter is the manifestation of the isospin in graphene) is observed for the first time in samples of this kind at elevated temperatures. A pronounced pattern of Shubnikov–de Haas oscillations is observed in strong magnetic fields (up to 30 T). This pattern demonstrated fourfold carrier spectrum degeneracy due to the double spin and double valley degeneracies. Also, the manifestation of the Berry phase is observed. The effective electron mass is estimated to be m* = 0.08m0, which is characteristic of graphene with a high carrier concentration.

A theory of spin-electromagnetic wave spectrum has been developed for the thin-film ferrite-ferroelectric structure based on a coplanar transmission line (TL). The dispersion relation was derived through analytical solution of the full set of Maxwell’s equations utilizing a method of approximate boundary conditions. The theory was used for numerical simulation of the transmission characteristics of the periodic multiferroic heterostructures containing the coplanar TL with a periodic variation of its width. We named these heterostructures “electromagnonic crystals.” The transmission characteristics of the electromagnonic crystals were calculated by the transfer-matrix method. The obtained results show that a high microwave signal rejection of more than 30 dB appears in the electromagnonic crystals due to the Bragg reflections. The distinctive features of the proposed electromagnonic crystals are the thin-film planar topology and dual tunability of the electromagnonic band-gap positions.

Transport characteristics of sodium alginate (SA) membranes cross-linked with CaCl2 and modified with fullerenol and fullerene derivative with L-arginine for pervaporation dehydration were improved applying various approaches, including the selection of a porous substrate for the creation of a thin selective SA-based layer, and the deposition of nano-sized polyelectrolyte (PEL) layers through the use of a layer-by-layer (Lbl) method. The impacts of commercial porous substrates made of polyacrylonitrile (PAN), regenerated cellulose, and aromatic polysulfone amide were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), standard porosimetry method, and water filtration. The effects of PEL combinations (such as poly(sodium 4-styrene sulfonate) (PSS)/SA, PSS/chitosan, PSS/polyacrylic acid, PSS/poly(allylamine hydrochloride)) and the number of PEL bilayers deposited with the Lbl technique on the properties of the SA and SA/fullerene derivative membranes were studied by SEM, AFM, and contact angle measurements. The best characteristics were exhibited by a cross-linked PAN-supported SA/fullerenol (5%) membrane with five PSS/SA bilayers: permeation flux of 0.68–1.38 kg/(m2h), 0.18–1.55 kg/(m2h), and 0.50–1.15 kg/(m2h), and over 99.7, 99.0, and 89.0 wt.% water in the permeate for the pervaporation dehydration of isopropanol (12–70 wt.% water), ethanol (4–70 wt.% water), and tetrahydrofuran (5.7–70 wt.% water), respectively. It was demonstrated that the mutual application of bulk and surface modifications essentially improved the membrane’s characteristics in pervaporation dehydration.

We propose a ferromagnetic Heusler alloy that can switch between a metal and a half-metal. Thiseffect can provide tunable spintronics properties. Using the density functional theory (DFT) withreliable implementations of the electron correlation effects, we find Mn2ScSi total energy curvesconsisting of distinct branches with a very small energy difference. The phase at low lattice crystalvolume is a low magnetic half-metallic state while the phase at high lattice crystal volume is a highmagnetic metallic state. We suggest that the transition between half-metallic and metallic statescan be triggered by a triaxial contraction/expansion of the crystal lattice or by an external magneticfield if we assume that the lattice is cubic and remains cubic under expansion/contraction. However,the phase at high volume can also undergo an austenite-martensite phase transition because of thepresence of Jahn-Teller active3delectrons on the Mn atoms., Comment: Supplementary materials is located on https://journals.aps.org/prb/supplemental/10.1103/PhysRevB.103.054414

By combining the 3D printing, electroplating and chemical vapor deposition processes we fabricated “bubble wrap” polymer nanomembrane covered with multilayered graphene. Such a metasurface composed of array of graphene hemispheres shows extremely broadband and almost perfect absorption in terahertz (THz) 2 frequency range being robust against macroscopic structural defects including holes and volcanic-like hats on hemispherical metaatoms. The developed theory perfectly explains our experimental findings including virtual independence of the metasurface transmittivity, reflectivity and absorptivity on the angle of incidence in terms of the plasmon dark mode formation. Our approach enables the THz perfect absorber that covers a frequency range spanning from few hundreds of GHz to 1.2 THz, and even more, while the proposed fabrication technique can also be employed in numerous applications that require free standing corrugated graphene/polymer nanomembranes.

The present work focuses on the effect of vanadium dioxide (VO2) films exhibiting a metal–insulator transition (MIT) on the performance characteristics of the magnetic multilayers. It has been shown that the MIT provides a novel mechanism for controlling the microwave spin-wave dynamics in the yttrium iron garnet (YIG) films. In particular, the low and high levels of microwave attenuation of spin waves transmitted through the YIG–VO2 bilayer has been observed due to a variation of the VO2 conductivity within a narrow temperature range. This effect has been utilized to realize fully reconfigurable magnonic crystals composed of the thickness-modulated YIG and regular VO2 films. A promising functionality of the proposed waveguiding structures arises from a controllability of wave intensity, which provides an altering of the frequency response from an original band structure to a full rejection of spin waves. Numerical simulations taking into account both the YIG film saturation magnetization and the VO2 film conductivity have confirmed the experimentally observed spin-wave dynamics. An interest in ferrite–VO2 bilayers arises not only from possible practical applications but also from a variety of fundamental scientific problems devoted to the physics of wave phenomena in planar thin-film magnetic multilayers. Post-print / Final draft

We discuss the interplay between magnetic and structural degrees of freedom in elemental Mn. The equilibrium volume is shown to be sensitive to magnetic interactions between the Mn atoms. While the standard generalized gradient approximation underestimates the equilibrium volume, a more accurate treatment of the effects of electronic localization and magnetism is found to solve this longstanding problem. Our calculations also reveal the presence of a magnetic phase in strained $\ensuremath{\alpha}$-Mn that has been reported previously in experiments. This new phase of strained $\ensuremath{\alpha}$-Mn exhibits a noncollinear spin structure with large magnetic moments.

We present a theoretical analysis of the split-off states emerging due to a tunnel coupling between a remote bound state and a semiconductor quantum well (QW). The on-site Coulomb repulsion and the spin splitting of the bound state have been considered. The split-off states emerge in the band gap of the QW and reveal themselves as two solitary peaks in the photoluminescence (PL) from the QW. The peaks have opposite circular polarization and their spectral position strongly depends on the tunnel coupling strength. We suggest a mechanism of ultrafast PL polarization switching by means of electrical modulation of the tunnel coupling by an external gate. The obtained results open a new possibility for the spin and optical polarization control in nanoscale systems.

The stability of the nonmodulated martensitic phase, the austenitic Fermi surface, and the phonon dispersion relations for ferromagnetic ${\mathrm{Ni}}_{2}\mathrm{MnGa}$ are studied using density functional theory. Exchange-correlation effects are considered with various degrees of precision, starting from the simplest local spin density approximation (LSDA), then adding corrections within the generalized gradient approximation (GGA), and finally, including the meta-GGA corrections within the strongly constrained and appropriately normed (SCAN) functional. We discuss a simple procedure to reduce a possible overestimation of magnetization and underestimation of nesting vector in SCAN by parametrically decreasing self-interaction corrections.

Novel mixed-matrix membranes based on polyvinyl alcohol and its composites with carboxyfullerene were developed. Carboxyfullerene was simultaneously used as a modifier and a cross-linker for polyvinyl alcohol. The structural properties of the developed composites were studied by nuclear magnetic resonance, X-ray diffraction analysis, scanning electron microscopy, and sorption experiments. Thermal properties and stability were investigated by thermogravimetric analysis and differential scanning calorimetry. Surface features were studied by measuring the contact angles by water. The transport properties of the developed membranes were studied in ethanol-water mixtures separation by pervaporation (4.4–90 wt.% water in the feed) at different temperatures (22, 35, 50 °C). All membranes were selective with respect to water. The optimal transport properties were obtained for the PVA-carboxyfullerene (3.5 wt.%) membranes containing catalyst p-toluenesulfonic acid.

Ferromagnetic resonance (FMR) and coaxial line techniques are employed for studying the high-frequency magnetic properties of thin Fe films deposited onto a flexible polymer substrate by magnetron sputtering. Multiple resonances are observed in the FMR spectra measured in X frequency range for films with thickness from 0.1 to 2.0 μm. The resonance magnetic fields are found to depend on of the film thickness and on the orientation of external magnetic field relative to the film plane. The variation of the FMR parameters with the layer thickness may be attributed to differences in the shape and size of nanocrystallites formed during the deposition of films of different thicknesses. Low-field resonance modes are found in addition to the homogeneous FMR of saturated magnetization. Qualitative agreement is observed between values of the resonance magnetic fields determined by FMR and coaxial line techniques.

The quaternary chalcogenides, attracting much attention in recent time as promising solar energy materials, permit an effective optimization of their composition by the Ge incorporation. In particular, this implies an interest to the Cu2ZnGeS4 compound, which utilization requires, however, a deeper understanding of its electronic properties in general. Here, we investigate magnetotransport of the p-type Cu2ZnGeS4 single crystals, including resistivity, ρ (T), magnetoresistance (MR) and Hall effect, in pulsed magnetic fields up to B = 20 T. The Mott variable-range hopping charge transfer has been established within a broad temperature interval of T between ∼100 and 200 K by investigations of ρ (T) in zero field. The positive and negative contributions to MR have been observed, attributing them to shrinkage of the impurity wave functions by the magnetic field and to the destructive interference of the hopping charge carriers, respectively. Observation of the negative Hall coefficient, RH (T), exhibiting the dependence close to that of ρ (T), gives a strong support to the Mott conduction mechanism in our p-type Cu2ZnGeS4 material. In addition, the conductivity, connected with thermal activation of holes on the mobility edge, Ec, has been identified both below and above the Mott conduction interval. Finally, the joint analysis of the ρ (T) and MR data has yielded a series of important microscopic parameters. These include such details of the hole spectrum in the acceptor band, as its semi-width, W, the density of localized states, g (μ), at the Fermi level, μ, the positions of μ and Ec, as well as values of the localization radius of holes, a, and of the acceptor concentration, NA.

We have studied the properties of relatively thick (about 120 nm) magnetic composite films grown by pulsed laser deposition using the eutectic compound (GaSb)0.59(MnSb)0.41 as target for sputtering. For the studied films we have observed ferromagnetism and an anomalous Hall effect above room temperature, confirming the presence of spin-polarized carriers. Electron microscopy, atomic and magnetic force microscopy results suggest that the films under study have a homogenous columnar structure in the bulk while MnSb inclusions accumulate near the surface. This is in good agreement with the high mobility values of charge carriers. Based on our data we conclude that the magnetic and magnetotransport properties of the films at room temperature are defined by the MnSb inclusions.

Numerous attempts to develop an efficient anti-cancer agent are focusing on the design of multifunctional objects with synergistic theranostic treatments and minimal side effects. The most prospective treatments which can be used in combination are chemotherapy, photothermal therapy, and photodynamic therapy. To avoid collateral damage, it is important to control local temperature during the treatment procedure. In this work, we demonstrate how free-based and zinc-containing porphyrins can be used as contactless luminescence thermometers. Thermal sensing was provided based on two approaches: ratiometric and lifetime-based techniques. Thermometric performances of suggested temperature sensors including relative sensitivity and temperature resolution were calculated and compared. Keywords: Porphyrins, Thermometry, Luminescence, Lifetime, Sensor

The energy structure of the Mn acceptor, which is a complex of Mn2+ ion plus valence band hole, is investigated in the external magnetic field and under presence of an uniaxial stress has been studied. The spin-flip Raman spectra are studied under resonant excitation of exciton bound to the Mn acceptor. The gfactors of the ground F = 1 and the first excited F = 2 states are determined and selection rules for the optical transitions between the acceptor states are described. The value of the random field (stress or electric field) acting on manganese acceptor and the deformation potential for the exchange interaction constant of the Mn2+ + hole complex are obtained. A theoretical model is developed that takes into account the influence of random internal and uniaxial external stress and magnetic field. The proposed model describes well the lines of spin-flip Raman scattering of Mn acceptor.

Ni50Mn35In14.25B0.75 is a typical representative of the family of metamagnetic In-based Heusler alloys which shows large magnetocaloric effects generated from first order magnetostructural and ferromagnetic-paramagnetic transitions. For this alloy, a study of the adiabatic temperature change ΔTad by a direct method and through thermomagnetic measurements in magnetic fields up to 14 T has been performed. It has been shown that the rate of heating/cooling can affect the magnitude and sign of ΔTad. The application of magnetic fields larger than 12 T (on cooling) results in the “kinetic arrest” of the ferromagnetic austenitic phase. The effects of the temperature and magnetic history, and kinetic effects, on ΔTad of these Ni-Mn-In-based Heusler alloys in high magnetic fields are discussed.

Transport properties of the kesterite-like single crystals of Cu2ZnSnS4, Cu2ZnSnxGe1−xSe4 and Cu2ZnGeS4 are investigated in pulsed magnetic fields up to B = 20 T. The Mott variable-range hopping (VRH) conduction is established by investigations of the resistivity, ρ (T), in all the materials mentioned above within broad temperature intervals of ΔTv4 ∼ 50–150 K, 50–250 K and 100–200 K, respectively. In addition, the Shklovskii-Efros VRH conductivity below Tv2 ∼ 3–4 K, the nearest-neighbour hopping (NNH) charge transfer between T ∼ 250–320 K and the conductivity by activation of holes on the mobility threshold at temperatures outside ΔTv4, respectively, are observed in these materials. In Cu2ZnSnS4, magnetoresistance (MR) contains only a positive contribution, connected mainly to a shrinkage of impurity wave functions by the magnetic field. At the same time, a negative contribution to MR, attributable to interference effects in VRH, is observed in Cu2ZnSnxGe1−xSe4 and, especially, in Cu2ZnGeS4. The joint analysis of the MR and ρ (T) data has yielded important electronic parameters of the materials. This includes widths of the acceptor band W and of the Coulomb gap Δ, the NNH activation energy En, the localization radius a, the acceptor concentration NA and the density of the localized states at the Fermi level, g (μ). A dramatic increase of a in Cu2ZnSnS4 with decreasing T is observed, whereas in Cu2ZnSnxGe1−xSe4 all the parameter W, En, g (μ), a and NA are non-monotonic functions of x. Finally, in Cu2ZnGeS4 the Hall coefficient RH (T) is negative (despite of the p-type conduction), exhibiting the dependence close to that of ρ (T) in the Mott VRH interval.

Resistivity, ρ(T), and magnetoresistance (MR) are investigated in graphene grown on SiC (0 0 0 1), at temperatures between T ~ 4-85 K in pulsed magnetic fields of B up to 30 T. According to the Raman spectroscopy and Kelvin-probe microscopy data, the material is a single-layer graphene containing ~20% double-layer islands with a submicron scale and relatively high amount of intrinsic defects. The dependence of ρ(T) exhibits a minimum at temperature T m ~ 30 K. The low-field Hall data have yielded a high electron concentration, n R ≈ 1.4 × 1013 cm-2 connected to intrinsic defects, and a mobility value of µ H ~ 300 cm2 (Vs)-1 weakly depending on T. Analysis of the Shubnikov-de Haas oscillations of MR, observed between B ~ 10-30 T, permitted to establish existence of the Berry phase β ≈ 0.55 and the cyclotron mass, m c ≈ 0.07 (in units of the free electron mass) close to expected values for the single-layer graphene, respectively. MR at 4.2 K is negative up to B ~ 9 T, exhibiting a minimum near 3 T. Analysis of MR within the whole range of B = 0-10 T below the onset of the SdH effect has revealed three contributions, connected to (i) the classical MR effect, (ii) the weak localization, and (iii) the electron-electron interaction. Analysis of the ρ(T) dependence has confirmed the presence of the contributions (ii) and (iii), revealing a high importance of the electron-electron scattering. As a result, characteristic relaxation times were obtained; an important role of the spin-orbit interaction in the material has been demonstrated, too.

The theoretical study considers chiral spin texture induced in a 2D electron gas (2DEG) by magnetic skyrmions. We calculate the electron gas spin density as a linear response to the exchange interaction between the 2DEG and the magnetization field of a magnetic skyrmion. Two physically distinct regimes occur. When the size of the skyrmion is larger than the inverse Fermi wavevector $k_F^{-1}$, the spin density response follows the magnetization profile of the skyrmion. In the opposite case of a small skyrmion the emerging spin structure of 2DEG has a characteristic size of $k_F^{-1}$ and the response becomes non-local, it can be viewed as chiral Friedel oscillations. At that, the emerging spin structure of the oscillations appears to be more complex than that of the skyrmion itself., 6 pages, 7 figures

One of the main challenges for the modern magnonics, which, as opposed to the conventional electronics, operates with quanta of spin waves in magnetically ordered materials—magnons—is energy efficient control of magnon transport on small time and space scales. The magnon propagation in a time-dependent periodic spatial potentials—dynamic magnonic crystals—paves a way to this aim. To date, dynamic manipulation of the magnonic crystals has been realized with electric current and optic control influence. However, both approaches show limited potential for reduction in energy consumption and miniaturization of magnonic circuits. Voltage (or electric field) control of magnon currents promises to be fast and low energy consuming. It can be achieved in ferrite-ferroelectric (multiferroic) heterostructures, where strong coupling of magnons and microwave photons constitutes new quasiparticles called electromagnons. Here, we present an experimental realization of a voltage-controlled dynamic electromagnonic crystal operating with electromagnons at microwave frequencies. Fast and energy-efficient control of magnon transport in magnonic crystals is one of the main challenges of modern magnonics. High performances for voltage control are expected but have so far only been predicted theoretically and investigated numerically. In this paper, the authors report of the first experimental realization of voltage-controlled magnon currents in a dynamic electromagnonic crystal.

Porphyrins and their fullerene complexes are promising materials for organic photovoltaic structures. However, the stability of the properties of organic components under hard radiation is poorly studied. Here, the influence of γ irradiation with medium (about 104 Gy) and large (107 Gy) doses on the photoluminescence of thin structurally perfect films of both pure porphyrin ZnTPP and ZnTPP/C60 composite films in the molar ratio of 1.3: 1 is investigated. It is shown that the intensity of the electronic radiative transition (626 nm) decreases under the effect of γ irradiation, and the dose dependence is threshold. The threshold dose is ~20 kGy for the ZnTPP films. The intensity of the electron-vibrational part of the spectral dependence of the PL (670–690 nm) for both types of samples decreased at initial irradiation doses and decreases less with a further increase in the irradiation dose than for the purely electron transition. The addition of a fullerene in nanocomposite films increases the threshold dose, after which the PL of the films started to degrade, by a factor of ~2.5. Herewith, the spectral components of the PL associated with the manifestation of the radiation transition of the fullerene C60 are more stable under γ irradiation.

Study of the local environment of certain ion is quite a complex problem. Due to the unique luminescent properties, Eu3+ ions can be used as a structural probe. In this paper, effect of doping concentration, excitation wavelength and excitation mechanism on asymmetry ratio was systematically studied using Y3Al5O12:Eu3+, YVO4:Eu3+ and Y2O3:Eu3+nanophosphors. The asymmetry ratio gives information about the local surrounding and environmental changes around the Eu3+ ions. Asymmetry ratios of YAG:Eu3+ and YVO4:Eu3+ nanopowders were calculated using standard technique and the obtained average values were found to be 0.75 and 8.2, respectively. However, it is found that standard method of asymmetry ratio calculation is suitable only for samples where all Eu3+ ions occupy one site. The “multisite model” of asymmetry ratio calculation was developed and used for Y2O3:Eu3+ nanocrystalline powders. Average value of asymmetry ratio for Eu3+ ions occupied “normal” sites is 6.0 and for Eu3+ ions occupied “defect” sites is 2.3.

Development of simple methods for preparation of polymeric electrode materials with nanofibrous network structure is a perspective way toward cheap supercapacitors with high specific capacitance and energy density. In this work one-pot synthesis of electroactive ternary composite based on polypyrrole, polyacrylamide and chitin nanofibers with beneficial morphology was elaborated. Ternary system demonstrates better electrochemical performance in comparison with both polypyrrole–polyacrylamide and polypyrrole–chitin binary composites. Possible mechanism of synergistic effect of simultaneous influence of polyacrylamide and chitin nanofibers on the formation of composite's structure is discussed. The highest attained specific capacitance of electroactive polypyrrole in ternary composite reached 249 F/g at 0.5 A/g and 150 F/g at 32 A/g. Symmetrical supercapacitor was assembled using the elaborated electrode material. High specific capacitance 89 F/g and good cycling stability with capacitance retention of 90% after 3000 cycles at 2 A/g were measured.

Nanoscale sub-degree non-contact temperature sensing is in high demand in many fields of science and technology. In this work, we report simply synthesized near-infrared emitting YVO4:Nd3+ nanoparticles as ratiometric luminescence thermal sensors. For thermal sensing, the dependences of the emission bands of 4F5/2 – 4I9/2 and 4F3/2 – 4I9/2 transitions from 123 up to 873 K were measured and calibrated as functions of the temperature. The thermal sensitivity was obtained and compared with others Nd3+-doped micro- and nanocrystals presented in the literature. Large energy gap between 4F5/2 and 4F3/2 levels used for nanothermometry leads to the significant enhancement of thermal sensitivity and widening of temperature sensing range compared with thermometers based on Stark sublevels intensity ratio. Effect of doping concentration on the thermal sensitivity was studied. Sub-degree thermal resolution obtained at 313 K and 673 K make YVO4:Nd3+ nanoparticles perspective material for accurate temperature sensing in both biological and technical applications.

The C-N samples were synthesized at 500 °C from melamine and four kinds of pitch. At 50–100 mass % of pitch all samples were single phase nitrogen solid solutions in graphitic carbon. Maximal detected concentration of 22.4 mass % N correspond to solid solution with formula C100H26.8N26.3O3.1. According to infrared spectroscopy the N atoms chaotically substitute carbon. The electric resistivity of samples with 22.4 mass % N was 1.3–67 Ω ∗ m, which is 100–1000 times lower than resistivity of corresponding graphitic carbon without doping (430–6700 Ω ∗ m). The resistivity of graphitic C3N4 is about 1011 Ω∗m.

Structural and luminescence properties of uncovered YVO4:Nd3+ and core-shell YVO4:Nd3+@SiO2 nanoparticles synthesized via modified Pechini technique were studied. Effect of silica shell thickness on steady state and kinetics luminescence parameters was investigated. Synthesized nanoparticles were used as non-contact optical thermometers operating in the second biological window upon heating-free 808 nm light by monitoring fluorescence intensity ratio between Nd3+ emission bands as a temperature-dependent parameter. Benefits of silica coating on the temperature sensing properties were clearly demonstrated. The best thermal sensitivity was found to be 0.40% K−1 at 299 K, the minimum temperature uncertainty was less than 0.5 K, which is enough for accurate temperature evaluation in the real systems.

Nanocrystalline aluminium magnesium spinel doped with europium ions powders were synthesized via modified Pechini method. The effect of synthesis conditions (calcination temperature and duration) on structural, morphological and luminescence properties of obtained nanopowders was studied. Both X-ray diffraction and Rietveld analysis showed that samples consist of only one crystalline phase – face-centred cubic spinel. The SEM and SLS analysis demonstrated that average particle size is about 50 nm. It was shown that the solubility limit of europium ions Eu3+ in MgAl2O4 nanocrystals depends on the calcination temperature. When europium is introduced into the aluminium magnesium spinel, the crystalline structure is disordered. It was found that unlike calcination temperature, duration of heat treatment does not affect powders properties. It was shown that strong structural and luminescence changes take place when calcination temperature is near 2/3 of MgAl2O4 melting temperature. The optimal conditions for synthesis nanopowders were determined as follows: Т1=600 °С t1=1.5 h, Т2=850 °С t2=2 h.