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Temperature-dependent angle-resolved photoemission spectroscopy (ARPES) was carried out on single-crystalline EuB6 samples. By measuring ARPES spectra in an extended Brillouin zone, a B 2p hole pocket centered at the X point is clearly observed, thus proving the semimetallic nature of EuB6. Below the Curie temperature TC, ARPES spectra show two B 2p bands of which separation is due to an exchange interaction between local Eu 4f and itinerant B 2p electrons. The exchange splitting becomes smaller as the temperature increases and disappears well above TC. Additionally, a diffuse structure near the Fermi level survives just above TC. Such behavior is well described by Monte Carlo simulations of a Kondo lattice model, thus supporting the formation of magnetic polarons in EuB6, which accounts for the resistivity upturn near above TC when lowering the temperature., Comment: 6 pages, 5 figures

The facile and rapid microwave-assisted method has been demonstrated to be effective in synthesizing manganese fluoride (MnF2) nanoparticles in binary mixtures of ethylene glycol and imidazolium-ba...

Controlling the density of electrons inside an insulator via the chemical potential is a cornerstone of modern electronics, enabling the electrical conductivity of semiconductors and the emergence of fascinating new properties linked with electronic correlations. The compound SmB6 has drawn widespread attention in recent years as the first insulator to feature both strong electronic correlations and topological quantum order1-7, potentially enabling a host of new phenomenologies as charge density is modified. However, chemical potential has not been experimentally controlled in studies to date of the electronic structure. Here we present an angle-resolved photoemission spectromicroscopy (μ-ARPES) study of SmB6 alloys, using the natural inhomogeneity of sample surfaces to create the analogue of a multi-dimensional doping series. The role of electronic correlations is observed in the interplay of the topologically ordered conducting states with one another and with the chemical potential. Higher doping is found to result in the transformation of these interdependencies as the disorder from impurities erodes quantum coherence. These findings set the stage for a holistic understanding of the interplay between strong correlations and topological features in the electron system. Moreover, they validate recent analyses suggesting that the electronic structure of SmB6 can present the key hallmarks of conventional electron doping, such as a Fermi surface, while nonetheless preserving long-range insulating character in electrical transport measurements8-10.

Strongly intertwined interaction among spin, orbital and charge degrees of freedom is the essence to induce emergent materials properties, and the investigation to understand their interplay has been actively pursued. In particular, resonant X-ray scattering technique has demonstrated powerful applications in unveiling their long-range ordering behavior with its enhanced sensitivity to the aforementioned degree of freedom. Here, we further demonstrated the spectroscopic application of the technique by providing experimental evidence to reveal spin polarizations in 4f and 5d orbital of the magnetic Tm ions with the orbital-selectivity, which introduced a route to understand fundamental mechanism of spin polarization in the compound. The enhanced sensitivity of the resonant X-ray scattering to various electric multipole transitions expects to find strong applications in studying various spin and polar ordering in materials to include high-order moments.

Temperature dependence of anisotropic tensor susceptibility (ATS) scattering intensities of GdB4 were measured near L-edges of Gd to investigate how spin ordering affects ATS. ATS scattering intensities for L2- and L3-edges show different temperature dependence below TN. At L3-edge the intensities reflect spin order parameter while intensities at L2-edge do not show noticeable change. The difference is explained in terms of spin-orbit coupling and isotropic distribution of spin-polarized 5d states of Gd ions. Above TN ATS scattering intensities demonstrate that thermal motions enhance charge distribution anisotorpy of Gd 5d states in paramagnetic phase.

Introduction Iron oxide magnetic nanoparticles (IONPs) have attracted considerable attention for various biomedical applications owing to their ease of synthesis, strong magnetic properties, and biocompatibility. In particular, IONPs can generate heat under an alternating magnetic field, the effects of which have been extensively studied for magnetic hyperthermia therapy. However, the development of IONPs with high heating efficiency, biocompatibility, and colloidal stability in physiological environments is still required for their safe and effective application in biomedical fields. Methods We synthesized magnetic IONP/polymer nanocomposites (MNCs) by embedding IONPs in a poly(L-lactic acid) (PLA) matrix via nanoemulsion. The IONP contents (Fe: 9–22 [w/w]%) in MNCs were varied to investigate their effects on the magnetic and hyperthermia performances based on their optimal interparticle interactions. Further, we explored the stability, cytocompatibility, biodistribution, and in vivo tissue compatibility of the MNCs. Results The MNCs showed enhanced heating efficiency with over two-fold increase compared to nonembedded bare IONPs. The relationship between the IONP content and heating performance in MNCs was nonmonotonous. The highest heating performance was obtained from MNC2, which contain 13% Fe (w/w), implying that interparticle interactions in MNCs can be optimized to achieve high heating performance. In addition, the MNCs exhibited good colloidal stability under physiological conditions and maintained their heating efficiency during 48 h of incubation in cell culture medium. Both in vitro and in vivo studies revealed excellent biocompatibility of the MNC. Conclusion Our nanocomposites, comprising biocompatible IONPs and PLA, display improved heating efficiency, good colloidal stability, and cytocompatibility, and thus will be beneficial for diverse biomedical applications, including magnetic hyperthermia for cancer treatment., Graphical Abstract

A well-known feature in transport data of the topological Kondo insulator SmB6 is the sign change in the Hall coefficient at 65 K. Carriers in SmB6 are known to be negative, but above 65 K, the Hall sign suggests that the carriers are positive. Here, we extend Hall measurements up to 400 K and observe that the Hall coefficient changes back to the correct (negative) sign at about 305 K. We interpret the anomalous sign of the Hall coefficient in the context of skew scattering arising from the strong correlations between the f and d electrons. At energy scales where the gap is closed, the number of d electrons in resonance with the f electrons at the Fermi energy varies. When a large proportion of d and f electrons are in resonance, skew scattering is dominant, leading to the observation of the positive sign, but when fewer are in resonance, conventional scattering mechanisms dominate instead.

AlFe2B2 was synthesized by arc-melting to investigate its magnetic properties. The magnetic properties of AlFe2B2 with impurities are different from those of pure AlFe2B2. In this study, an as-cast sample and an annealed sample followed by acid treatment were prepared to understand the magnetic properties of pure AlFe2B2. In the powder X-ray diffraction measurements, a pure AlFe2B2 phase was confirmed after annealing followed by acid treatment. Various magnetic properties were investigated by using superconducting quantum interference device (SQUID) measurements for the as-cast and the post-treated samples. Saturation magnetization and effective magnetic moments of the post-treated sample are close to the theoretical values of pure AlFe2B2. The maximum magnetic entropy change (˗ΔS) of pure AlFe2B2 is 6.95 J/kg∙K at 5 T. Pure AlFe2B2 shows a positive slope in the Arrott plots corresponding to a second-order magnetic transition. Magnetic transition temperatures estimated from dM/dT, the Arrott plots, and the Curie-Weiss law are mutually complementary.

Molecular-level ordering provides a powerful approach to enhancing the properties of materials. However, the precise arrangement of molecules in a bulk material is a considerable challenge. To overcome such limitations, hydrogen bonding-directed self-assembly has drawn a lot of attention due to its facile nature in controlling molecular-level order. In this study, we report ordering of the magnetic Fe centers achieved through hydrogen bonding between poly(4-vinylpyridine) (P4VP, MW 60 kDa) and 1,1′-ferrocenedicarboxylic acid (FDA). Co-dissolving P4VP and FDA in dry methanol leads to P4VP–FDA showing an unprecedented degree of order for both FDA and the polymer chain. Such an event of mutual assistance between a dicarboxylic acid and a high molecular weight polymer chain in building the ordered supramolecular architecture is rare. FDA is uniformly distributed in an ordered polymer matrix, with each Fe center in P4VP–FDA linked at the molecular-level through polymeric bridges in a face-centered cubic struct...

AlFe2B2 produced by using a conventional arc melter has a ferromagnetic material with a Curie temperature (TC) of around 300 K, but the arc-melt generates paramagnetic Al13Fe4 impurities during the synthesis of AlFe2B2. Impurities are brought to cause a decrease in magnetocaloric effects (MCEs). To investigate the effects of Al13Fe4 impurities on MCEs, we prepared and compared ascast and acid-treated samples, where the acid treatment was performed to remove the Al13Fe4 impurities. For the structural analysis, powder X-ray diffraction was carried out, and the measured data were subjected to a Rietveld refinement. The presence of Al13Fe4 impurities in the as-cast sample was observed in the phase analysis measurements. Magnetic properties were investigated by using Superconducting Quantum Interference Device (SQUID) measurements for the as-cast and the acid-treated AlFe2B2 samples. From isothermal magnetization measurements, Arrott plots were obtained showing that the transition of AlFe2B2 has a second-order magnetic phase transition (SOMT). The TC and the saturation magnetization increased for the acid-treated sample due to removal of the paramagnetic impurities. As a consequence, the magnetic entropy change (−ΔS) increased in the pure AlFe2B2 samples, but the full width at half maximum in the plot of −ΔS vs. T decreased due to the absence of impurities.

The frustrated magnet has been regarded as a system that could be a promising host material for the quantum spin liquid (QSL). However, it is difficult to determine the spin configuration and the corresponding mechanism in this system, because of its geometrical frustration (i.e., crystal structure and symmetry). Herein, we systematically investigate one of the geometrically frustrated magnets, the TbB4 compound. Using resonant soft x-ray scattering (RSXS), we explored its spin configuration, as well as Tb's quadrupole. Comprehensive evaluations of the temperature and photon energy/polarization dependences of the RSXS signals reveal the mechanism of spin reorientation upon cooling down, which is the sophisticated interplay between the Tb spin and the crystal symmetry rather than its orbit (quadrupole). Our results and their implications would further shed a light on the search for possible realization of QSL.

We investigate the roles of disorder on low-temperature transport in SmB$_6$ crystals grown by both the Al flux and floating zone methods. We used the inverted resistance method with Corbino geometry to investigate whether low-temperature variations in the standard resistance plateau arises from a surface or a bulk channel in floating zone samples. The results show significant sample-dependent residual bulk conduction, in contrast to smaller amounts of residual bulk conduction previously observed in Al flux grown samples with Sm vacancies. We consider hopping in an activated impurity band as a possible source for the observed bulk conduction, but it is unlikely that the large residual bulk conduction seen in floating zone samples is solely due to Sm vacancies. We therefore propose that one-dimensional defects, or dislocations, contribute as well. Using chemical etching, we find evidence for dislocations in both flux and floating zone samples, with higher dislocation density in floating zone samples than in Al flux grown samples. In addition to the possibility of transport through one-dimensional dislocations, we also discuss our results in the context of recent theoretical models of SmB$_6$., 22 pages, 4 figures

Tailoring various architectures of electrode material has been deemed a feasible route for improving the surface reactivity, the contact area between electrode and electrolyte, and enabling shortened electronic pathways to realize higher performance lithium-ion batteries. Here, we rapidly synthesized the manganese fluoride (MnF2) with various morphologies by microwave irradiation using ionic liquid as the fluoride source, soft template, and microwave absorber solvent. The hierarchical nanostructured MnF2 were optimized by controlling the purity of ionic liquid, microwave heating rate, and precursor concentration. The dominant factors influencing the morphologies of MnF2 were systematically investigated and relevant descriptions for the formation mechanism were suggested. Also, we demonstrated the abnormal high-capacity lithium-ion battery anode using the hierarchical nanostructured MnF2 anode based on the conversion mechanism. The prepared MnF2 anode yielded a maximum reversible specific capacity of 986 mAhg−1 at 0.1C after 30 cycles. This study provides a comprehensive understanding of the morphological control of the hierarchical structured MnF2 using the microwave-ionic liquid combination method for high-capacity lithium-ion battery anode.

After the theoretical prediction that ${\mathrm{SmB}}_{6}$ is a topological Kondo insulator, there has been an explosion of studies on the ${\mathrm{SmB}}_{6}$ surface. However, there is not yet an agreement on even the most basic quantities such as the surface carrier density and mobility. In this paper, we carefully revisit Corbino disk magnetotransport studies to find those surface transport parameters. We first show that subsurface cracks exist in the ${\mathrm{SmB}}_{6}$ crystals, arising both from surface preparation and during the crystal growth. We provide evidence that these hidden subsurface cracks are additional conduction channels, and the large disagreement between earlier surface ${\mathrm{SmB}}_{6}$ studies may originate from previous interpretations not taking this extra conduction path into account. We provide an update of more reliable magnetotransport data than the previous one (S. Wolgast et al., Phys. Rev. B 92, 115110) and find that the orders-of-magnitude large disagreements in carrier density and mobility come from the surface preparation and the transport geometry rather than the intrinsic sample quality. From this magnetotransport study, we find an updated estimate of the carrier density and mobility of $2.71\ifmmode\times\else\texttimes\fi{}{10}^{13}$ (1/${\mathrm{cm}}^{2}$) and 104.5 (${\mathrm{cm}}^{2}$/$\mathrm{V}\phantom{\rule{0.16em}{0ex}}\mathrm{sec}$), respectively. We compare our results with other studies of the ${\mathrm{SmB}}_{6}$ surface. By this comparison, we provide insight into the disagreements and agreements of the previously reported angle-resolved photoemission spectroscopy, scanning tunneling microscopy, and magnetotorque quantum oscillations measurements.

The effect of magnetic fields on the optical output power of flip-chip light-emitting diodes (LEDs) with InGaN/GaN multiple quantum wells (MQWs) was investigated. Films and circular disks comprising ferromagnetic cobalt/platinum (Co/Pt) multilayers were deposited on a p-ohmic reflector to apply magnetic fields in the direction perpendicular to the MQWs of the LEDs. At an injection current of 20 mA, the ferromagnetic Co/Pt multilayer film increased the optical output power of the LED by 20% compared to an LED without a ferromagnetic Co/Pt multilayer. Furthermore, the optical output power of the LED with circular disks was 40% higher at 20 mA than the output of the LED with a film. The increase of the optical output power of the LEDs featuring ferromagnetic Co/Pt multilayers is attributed to the magnetic field gradient in the MQWs, which increases the carrier path in the MQWs. The time-resolved photoluminescence measurement indicates that the improvement of optical output power is owing to an enhanced radiative recombination rate of the carriers in the MQWs as a result of the magnetic field gradient from the ferromagnetic Co/Pt multilayer.

2D correlation analysis (2DCOS) and principal component analysis (PCA) have been performed on temperature-dependent Raman spectra from 12 K to 300 K of SmB6 single crystals grown from Boron with a purity of 99.9% (3N) or 99.9999% (6N). Significant differences in the Raman spectra of SmB6(3N) and SmB6(6N) are observed. The Raman active T2g, Eg, and A1g modes of SmB6(3N) are broader and shift to higher wavenumbers compared with those of SmB6(6N). The results of 2DCOS and PCA on temperature-dependent Raman spectra of SmB6(3N) and SmB6(6N) give us further information. We find that all the T2g, Eg, and A1g modes of SmB6(6N) are single bands, while those of SmB6(3N) show all doublet features. The appearance of multiple bands in Raman vibrational modes of SmB6(3N) sample implies that the structure of boron octahedra of the SmB6(3N) has lower symmetry than that of SmB6(6N). Our findings in 2DCOS and PCA of the Raman spectra strongly support the differences in the behavior of SmB6(3N) and SmB6(6N).

This article gives a brief description of metal oxides, acceptable for using in advanced conductometric gas sensors, as well as a consideration of approaches, that can be used to select metal oxides for the manufacture of devices intended to sensor market.

Localized spin-wave modes, which were thermally excited at a specific position in a triangular magnetic element, were investigated using micro-focused Brillouin light scattering in two saturated states, the buckle and Y-states, with an applied magnetic field of 0.24 T parallel and perpendicular to the basal edge, respectively. The measured frequency spectrum at a specific beam spot position, rather than an integrated spectrum, was analyzed by comparing it with the simulation data at a precisely selected position within the beam spot area. The analyzed results were used to plot a two-dimensional intensity map and simulation spatial profile to verify the validity of the analysis. From the analysis process, two localized spin-wave modes in a triangular magnetic element were successfully identified near the apex region in the buckle state and near the basal edge region in the Y-state.

A new approach to controlling the structure of silica films formed by the sol–gel method is proposed. The models of formation of the silica coatings, obtained from the sol, cooled to the liquid nitrogen temperature, have been developed. It was found that as a result of this process, one can obtain aggregates consisting of spindle-shaped nanoparticles with sizes of the order of tens of nanometers, formed during the preparation of sol. The proposed model predicts aggregate sizes that depend on the synthesis conditions. The results obtained can be useful for the preparation of films with controlled degree of nanocrystallite’s agglomeration.

Resonant X-ray scattering measurements for a GdB4 single crystal have been carried out at Gd L 3- and L 2-edges. Branching ratios between x-ray scattering intensities at two x-ray energies are different for resonance peaks. Their analysis shows different anisotropic characters of 5d electron states of Gd ions corresponding to the peaks.

Electrical spin switching in an antiferromagnet is one of the key issues for both academic interest and industrial demand in new-type spin devices because an antiferromagnetic system has a negligible stray field due to an alternating sign between sub-lattices, in contrast to a ferromagnetic system. Naturally, questions arise regarding how fast and, simultaneously, how robustly the magnetization can be switched by external stimuli, e.g., magnetic field and spin current. First, the exploitation of ultrafast precessional motion of magnetization in antiferromagnetic oxide has been studied intensively. Regarding robustness, the so-called inertia-driven switching scenario has been generally accepted as the switching mechanism in antiferromagnet system. However, in order to understand the switching dynamics in a canted antiferromagnet, excited by magnetic field, accurate equation of motion and corresponding interpretation are necessary. Here, we re-investigate the inertia-driven switching process, triggered by the strict phase matching between effective driving field, dh/dt, and antiferromagnetic order parameters, l. Such theoretical approaches make it possible to observe the static parameters of an antiferromagnet, hosting Dzyaloshinskii–Moriya (DM) interaction. Indeed, we estimate successfully static parameters, such as DM, exchange, and anisotropy energies, from dynamical behaviour in YFeO3, studied using terahertz time-domain spectroscopy.

The features of conductometric gas sensors based on metal oxide composites are considered. The methods of the composites forming and the advantages of their using in the development of gas sensors are discussed. It is given the analysis of the factors that reduce the effectiveness of the composite using in conductometric gas sensors and can restrict application of nanocomposites in these devices. Technology features of composite synthesis and device fabrication, which should be taken into account while designing and fabricating sensors based on metal oxide composites, are considered. The mechanisms explaining the operation of conductometric gas sensors based on metal oxide composites are also discussed.

In this work it was studied the influence of cross-interference effects between hydrogen and ozone on the performances of the SnO 2 -based thin film gas sensors. The SnO 2 films with different thickness were deposited by spray pyrolysis. It was shown that the interference of gases was not a simple arithmetic addition of two effects related to the influence of individual gases on the sensor parameters. Interference of gases depends on many factors, including the concentration of the interacting gases, the film structure and the surface properties of the gas-sensitive material. Therefore it is difficult to predict this effect basing on the results obtained during the sensor testing to individual gases. It was also found that the air ozonization could be used to optimize the sensor parameters, i.e. to increase sensitivity and decrease the time constants of response and recovery. In addition, we have proposed temperature conditions, providing an improvement of the sensor selectivity when detecting hydrogen and ozone.

This article describes in detail the SnO2 and In2O3 metal oxides as materials for designing solid state conductometric ozone sensors. The main focus of this article is on the description of the SnO2 and In2O3 films' structural parameters important for gas sensor design and on the establishment of the main regularities of the film parameters influence on the sensor characteristics. Advantages and disadvantages of approaches used for optimization of ozone sensor parameters are also analyzed. In particular, surface modification, bulk doping of SnO2 and In2O3, and the use of 1D structures and hybrid materials are considered. The main factors, controlling parameters of SnO2- and In2O3-based ozone sensors, are determined, and recommendations for the process of the SnO2 and In2O3 films deposition, facilitating the search of the film parameters and the fabrication technologies that optimize the ozone sensor performance, are formulated.

In this paper the results of structural analysis of the SnO 2 and In 2 O 3 films deposited by spray pyrolysis are presented. The main goals of this analysis are summarizing the results obtained in this field, highlighting a correlation between parameters of film deposition and the material structure and formulating some general regularities, typical for metal oxides. Peculiarities and mechanisms of pyrosol deposition as well as advantages and disadvantages of this technology for deposition of the films with required parameters were also discussed. It is shown that this technology has great potential for controlling structural parameters of metal oxides such as thickness, the grain size, texturing, roughness, the grain faceting and the porosity.

Synchrotron radiation photoemission study of C 1s line of (111) In 2 O 3 surface was carried out under HV (high vacuum) doses of oxygen, carbon monoxide and water. Gas interaction with the surface was activated by heating of In 2 O 3 monocrystalline film at temperatures of 160 or 250 °C. The study of complex structure of C 1 s line and evolution of its fine components allowed to establish their nature and to propose possible surface adsorbed species and reactions, including a direct chemisorption and dissociation of CO molecules. Reduction or oxidation of the surface determines whether the first (chemisorption) or the second (dissociation) process takes place. The latter is responsible for additional formation of ionosorbed oxygen. Both processes have not been previously reported for In 2 O 3 and for conductive metal oxides.

In the development of spin-based electronic devices, a particular challenge is the manipulation of the magnetic state with high speed and low power consumption. Although research has focused on the current-induced spin-orbit torque based on strong spin-orbit coupling, the charge-based and the torque-driven devices have fundamental limitations: Joule heating, phase mismatching and overshooting. In this work, we investigate numerically and theoretically alternative switching scenario of antiferromagnetic insulator in one-dimensional confined nanowire sandwiched with two electrodes. As the electric field could break inversion symmetry and induce Dzyaloshinskii-Moriya interaction and pseudo-dipole anisotropy, the resulting spiral texture takes symmetric or antisymmetric configuration due to additional coupling with the crystalline anisotropy. Therefore, by competing two spiral states, we show that the magnetization reversal of antiferromagnets is realized, which is valid in ferromagnetic counterpart. Our finding provides promising opportunities to realize the rapid and energy-efficient electrical manipulation of magnetization for future spin-based electronic devices., Comment: 19 pages, 5 figures

The interplay of charge, spin, orbital and lattice degrees of freedom has recently received great interest due to its potential to improve the magnetocaloric effect (MCE) for the purpose of magnetic cooling applications. Here we propose a new mechanism for a giant inverse MCE in rare-earth tetraborides, especially for Ho1-xDyxB4 (x = 0.0, 0.5, and 1.0). For x = 0.0, 0.5, and 1.0, the maximum entropy changes of the giant inverse MCE are found to be 22.7 J/kgK, 19.6 J/kgK, and 19.0 J/kgK with critical fields of 25 kOe, 40 kOe, and 50 kOe, respectively. It is remarkable that such a giant MCE is realized, even when applying a low magnetic field, which enables a field-tuned entropy change and brings about a significant advantage for several applications. For all compounds, we have systematically studied how the entropy changes as a function of the field and temperature and investigated their correlation with consecutive double transitions, i.e., the magnetic dipolar order at T = TN and the quadrupolar order at T = TQ (TQ < TN). We found that the maximum entropy change occurs at T = TQ and the critical field associated with the meta-magnetic transition, which is in good agreement with the experimental data. Thus, we elucidate that this unique behaviour is attributed to the strong coupling between magnetic dipoles and quadrupoles in the presence of strong spin-orbit coupling and geometric frustration. Our work offers new insights into both the academic interest of multipolar degrees of freedom in magnetic materials and the discovery of giant MCE with various applications for magnetic cooling systems., 25 pages, 12 figures

The rare earth magnetic order in pure and doped Ho(1−x)Er x Ni2B2C (x = 0, 0.25, 0.50, 0.75, 1) single crystal samples was investigated using magnetization and neutron diffraction measurements. Superconducting quaternary borocarbides, RNi2B2C where R = Ho, Er , are magnetic intermetallic superconductors with the transition temperatures ∼10 K in which long range magnetic order develops in the same temperature range and competes with superconductivity. Depending on the rare earth composition the coupling between superconductivity and magnetism creates several phases, ranging from a near reentrant superconductor with a mixture of commensurate and incommensurate antiferromagnetism to an incommensurate antiferromagnetic spin modulation with a weak ferromagnetic component. All of these phases coexist with superconductivity. RKKY magnetic interactions are used to describe the magnetic orders in the pure compounds. However, the doping of Er on Ho sites which have two strong magnetic moments with two different easy directions creates new and complicated magnetic modulations with possible local disorder effects. One fascinating effect is the development of an induced magnetic state resembling the pure and doped R 2CuO4 cuprate with R = Nd and Pr.

Emergence of anomalous weak ferromagnetism in geometrically frustrated magnetic system of R 1− x Y x B 4 ( R = Tb and Dy) is quite interesting [Phys. Rev. B 91 , 024414 (2015)]. In order to study the weak ferromagnetism in other compounds, the magnetic properties of R 1− x Y x B 4 ( R = Sm, Gd, and Er) were investigated. The anomalous weak ferromagnetism was also found to occur in all compounds, R 1− x Y x B 4 ( R = Sm, Gd, and Er). The weak ferromagnetism is revealed in the magnetic easy plane, (001), for R 1− x Y x B 4 ( R = Sm and Gd) and along the magnetic easy axis, [001], for R 1− x Y x B 4 ( R = Er). The magnitude of saturated magnetic moment at T = 2 K shows a strong dependence on Y-concentration, i.e., the maximum magnitude occurs at x ≈ 0.3 for all compounds. The general magnetic properties of weak ferromagnetism is quite similar to the weak ferromagnetism in R 1− x Y x B 4 ( R = Tb, Dy). Therefore, it is experimentally demonstrated that the emergence of weak ferromagnetism, induced by non-magnetic substitution in a magnetically frustrated system, is the universal feature in R B 4 compounds.

The features of conductometric gas sensors based on metal oxide composites are considered. The methods of the composites forming and the advantages of their using in the development of gas sensors are discussed. It is given the analysis of the factors that reduce the effectiveness of the composites using in conductometric gas sensors, which should be taken into account while designing and fabricating sensors based on metal oxide composites. The mechanisms explaining the operation of conductometric gas sensors based on metal oxide composites are also discussed.

DyNi 2 B 2 C is the only compound in the R Ni 2 B 2 C ( R = rare-earth element) series where superconductivity at T c ∼6.2 K coexists with the antiferromagnetic ordering below the Neel temperature T N ∼10.3 K. This system is of great interest because superconductivity rarely coexists with magnetic ordering. 11 B pulsed nuclear magnetic resonance (NMR) measurements were performed at 8.0056 T to investigate the local electronic structures and 4f spin dynamics of DyNi 2 B 2 C powders and single crystals. The spectrum for the single crystal showed three narrow resonance peaks at 295 K due to the nuclear Zeeman splitting of a nuclear spin I = 3/2 with quadrupolar perturbation. The 11 B NMR Knight shift of the single crystal was very large and highly anisotropic at K = −0.60% and +0.27% for the fields parallel and perpendicular, respectively, to the c -axis at 295 K. Considering the anisotropy of the Knight shift, we were able to simulate the 11 B NMR power pattern that agreed well with the measured spectrum. The linewidth for DyNi 2 B 2 C was also large and anisotropic, and the linewidth value increased rapidly at low temperatures. The 11 B NMR shift and linewidth were found to be proportional to the magnetic susceptibility, indicating that the hyperfine field at the B site originates from the 4 f spins of Dy. Above T N , the values for 1/ T 1 (the spin-lattice relaxation rate) and 1/ T 2 (the spin-spin relaxation rate) were very large, showing slight increases at low temperatures. Below T N , the values of 1/ T 1 and 1/ T 2 were suppressed significantly because of the slowing of the 4 f spin fluctuation. This confirmed the huge change in Dy 4f spin dynamics across the antiferromagnetic transition.

In this paper, thermoelectric properties of nanoscaled In2O3:Sn films are considered. The limitations that may appear during the usage of such materials in devices developed for the market of thermoelectric generators and refrigerators are also analysed. It is shown that nanoscaled In2O3:Sn is a promising material for thermoelectric applications. It is also established that insufficient thermal stability of nanostructured materials is the main limitation of these materials application in high-temperature thermoelectric converters. Optimization of grain boundary parameters and the usage of specific surrounding atmosphere can significantly improve the efficiency of thermoelectric conversion of nanostructured materials in the region of intermediate temperatures.

In this work, an approach to the numerical study of the thermoelectric parameters of nanoscale indium tin oxide (ITO, Sn content

Samarium hexaboride (SmB6), which lies in the mixed valence regime in the Anderson model, has been predicted to possess topologically protected surface states. The intensive investigations on SmB6 have brought up the long standing questions about the discrepancy between the surface and bulk electronic properties in rare-earth compounds in general. Here, we investigate and eventually clarify this discrepancy in the particular case of SmB6 by the photoemission core-level spectra. We focus on the change in both Sm and B states depending on time, temperature, probing depth, and surface termination on the cleaved (100) surface. Our spectra show that the unusual time-dependent change in the Sm valence occurs within a period of hours, which is not related to the adsorption of residual gases. Moreover, we observe a reduction of the surface feature in the B and Sm states on the same timescale accompanied by the formation of a subsurface region. Thus, it indicates the relatively slow charge redistribution between the surface and subsurface regions. Our findings demonstrate that the f states is strongly involved in the surface relaxation.

A study of the surface and gas–sensitive properties of In 2 O 3 films modified with gold nanoparticles and synthesized by the successive ionic layer deposition (SILD) method was conducted. In 2 O 3 films were prepared using the spray pyrolysis method. The gas-sensing characteristics were tested using CO, H 2 , and O 3 as target gases. It has been shown that the surface modification with gold nanoparticles gives the opportunity to optimize the response of In 2 O 3 -based gas sensors to both reducing (CO, H 2 ) and oxidizing (O 3 ) gases. It has been found that the sensitizing effect during ozone detection was significantly higher than the effect during CO and H 2 detection. It has been demonstrated that the sensitizing effect depended on the number of SILD cycles used for gold nanoparticle deposition and was maximal for the In 2 O 3 surface decorated with gold nanoparticles with the smallest size. The mechanism of the gold nanoparticles' influence on the gas-sensing properties of the In 2 O 3 films is also discussed. It is suggested that to explain the observed effects, we have to consider both the “electronic” and “chemical” mechanisms of sensitization. Suggestions for studies to be carried out to further improve both the understanding of the nature of the gas-sensitive effects and the parameters of In 2 O 3 :Au-based gas sensors are also formulated.

Thermoelectric properties of In 2 O 3 –SnO 2 -based multi-component metal oxide films formed by spray pyrolysis method are studied. It is shown that the introduction of additional components such as gallium and zinc can control the parameters of the deposited layers. At that, the doping with gallium is more effective for optimization of the efficiency of the thermoelectric conversion. The explanation of the observed changes in the electro-physical and thermoelectric properties of the films at the composition change is given. It is found that the main changes in the properties of multicomponent metal oxide films take place at concentrations of dopants which correspond to their limit solubility in the dominant oxide.

We report the increase of the optical output power of InGaN/GaN multiple quantum well (MQW) flip-chip blue light-emitting diodes (LEDs) using cobalt–iron (CoFe) ferromagnetic layers. The CoFe alloy layer is deposited on a p-ohmic reflector of the flip-chip LEDs to apply a magnetic field in the MQWs. The optical output power of LEDs with a CoFe layer after magnetization is increased by 23% at an injection current of 20 mA compared with LEDs that have a CoFe layer before magnetization. The time-resolved photoluminescence spectra and magnetic field simulations indicated that the improvement of the optical output power of the LEDs is attributed to an enhanced radiative recombination rate in the MQWs by the additional drift of carriers in the MQWs due to the gradients of the magnetic field of the CoFe ferromagnetic layer.

The coupled system of multi-degrees of freedom, such as charge, spin, orbital and lattice, has recently received much attention due to its potential to improve the magnetocaloric effect (MCE). The exotic inverse MCE was observed in rare-earth tetraborides of Ho1-xDyxB4 (x = 0.0, 0.5, and 1.0), associated with a strong coupling between magnetic dipoles and orbital quadrupoles in the strong spin-orbit coupling and geometric frustration. Here, the magnetism and magnetocaloric effects of ErB4 and TmB4 are investigated. It shows the maximum entropy changes of 11.4 J/kgK, and 12.6 J/kgK with the field of ΔH ≈ 40 kOe (H∥c) in ErB4 and TmB4, respectively. The field- and temperature-dependence of the entropy change is found to be quite different from those of the conventional MCE. And the entropy change is also found to have strong correlation with the field induced meta-magnetic transition. Because the field induced transition is due to magnetic moment reorientation, which is strongly coupled with quadrupole moment, the abnormal MCE of ErB4 and TmB4 is attributed to the dipole-quadrupole interaction and magnetic frustration. Thus, it supports the fact that the strong coupling between quadrupole and magnetic dipole moments plays important role in the exotic inverse MCE in rare-earth tetraboride system.

Spin-based electronic devices on polymer substrates have been intensively investigated because of several advantages in terms of weight, thickness, and flexibility, compared to rigid substrates. So far, most studies have focused on maintaining the functionality of devices with minimum degradation against mechanical deformation, as induced by stretching and bending of flexible devices. Here, we applied repetitive bending stress on a flexible magnetic layer and a spin-valve structure composed of Ta/NiFe/CoFe/Cu/Ni/IrMn/Ta on a polyimide (PI) substrate. It is found that the anisotropy can be enhanced or weakened depending upon the magnetostrictive properties under stress. In the flat state after bending, due to residual compressive stress, the magnetic anisotropy of the positive magnetostrictive free layer is weakened while that of the pinned layer with negative magnetostriction is enhanced. Thus, the magnetic configuration of the spin-valve is appropriate for use as a sensor. Through the bending process, we design a prototype magnetic sensor cell array and successfully show a sensing capability by detecting magnetic microbeads. This attempt demonstrates that appropriate control of stress, induced by repetitive bending of flexible magnetic layers, can be effectively used to modify the magnetic configurations for the magnetic sensor.

We investigate the effect of a magnetic field on red, green, and blue CdSe/ZnS quantum dot light-emitting diodes (QDLEDs). Circular multilayer ferromagnetic cobalt/platinum (Co/Pt) disks are deposited on a MgF2 layer covering an Al electrode, and a perpendicular magnetic field is applied to the QDs in the active layer. Carriers injected into the active layer are then trapped and efficiently recombined inside the QDs because of strong carrier localization caused by the perpendicular magnetic field. The luminescence of the QDLEDs in the multilayer increases by 33.31% at 7.5 V, 22.34% at 7.5 V, and 16.73% at 7.0 V compared with that of QDLEDs without the multilayer. The time-resolved photoluminescence of all the QDLEDs also indicates that their increased luminescence results from improved radiative recombination through the stronger carrier localization in the QDs.

Weyl semimetal is a topologically non-trivial phase of matter with pairs of Weyl nodes in the k-space, which act as monopole and antimonopole pairs of the Berry curvature. Two hallmarks of the Weyl metallic state are the topological surface state called the Fermi arc and the chiral anomaly. It is known that the chiral anomaly yields anomalous magnetotransport phenomena. In this study, we report the emergence of the type II Weyl semimetallic state in the geometrically frustrated non-collinear antiferromagnetic Shastry-Sutherland lattice (SSL) GdB4 crystal. When we apply magnetic fields perpendicular to the non-collinear moments in the SSL plane, Weyl nodes are created above and below the Fermi energy along the M-A line (τ-band) because the spin tilting breaks the time-reversal symmetry and lifts band degeneracy while preserving C 4 z or C 2 z symmetry. The unique electronic structure of GdB4 under magnetic fields applied perpendicular to the SSL gives rise to a non-trivial Berry phase, detected in de Haas-van Alphen experiments, and chiral anomaly–induced negative magnetoresistance. The emergence of the magnetic field–induced Weyl state in the SSL presents a new guiding principle to develop novel types of Weyl semimetals in frustrated spin systems.

Antiferromagnetic insulators (AFIs) have attracted much interest from many researchers as promising candidates for use in ultrafast, ultralow-dissipation spintronic devices. As a fast method of reversing magnetization, precessional switching is realized when antiferromagnetic N\'eel orders $l=({\mathbf{s}}_{1}+{\mathbf{s}}_{2})/2$ surmount the magnetic anisotropy or potential barrier in a given magnetic system, which is described well by the antiferromagnetic plane pendulum (APP) model. Here, we report that, as an alternative switching scenario, the direct coupling of an electric field with Dzyaloshinskii-Moriya (DM) interaction, which stems from spin-orbit coupling, is exploited for optimal switching. We derive the pendulum equation of motion of antiferromagnets, where DM torque is induced by a pulsed electric field. The temporal DM interaction is found to not only be in the form of magnetic torques (e.g., spin-orbit torque or magnetic field) but also modifies the magnetic potential that limits $l$ 's activity; as a result, appropriate controls (e.g., direction, magnitude, and pulse shape) of the induced DM vector realize deterministic reversal in APP. The results present an approach for the control of a magnetic storage device by means of an electric field.

In this report it is being discussed approaches for designing the SnO2 and In2O3 ozone sensors based on the film parameters optimization. It was considered the influence of the conditions of the SnO2 and In2O3 films deposition by spray pyrolysis method and the parameters of those films on operating characteristics of ozone sensors. Main factors, controlling operating characteristics of thin film ozone sensors were determined. Recommendations to process of the SnO2 and In2O3 films deposition, promoting an attainment of optimal operating gas sensing properties, were formulated.