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Vacuum induction melted equi-atomic NiMn alloy has been studied through x-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD pattern of the as-solidified alloy may be matched with the tI2 η′-NiMn phase and the cF4 Ni3Mn phase simultaneously. In the TEM bright field image of the same alloy, alternating bright and dark contrast with chessboard-like appearance is observed. Electron diffraction patterns from the bright phase match with the tI2 NiMn phase. The electron diffraction patterns from the dark phase are related to the tetragonal phase with additional superlattice reflection along [110] and [112]. The crystal structure of the new phase has been found to be polymorphically related mP8 phase with space group P 2/m (a = 5.02 Å, b = 5.16 Å, c = 3.61 Å). The phase has not been reported so far in the Ni–Mn system. The chessboard-like morphology between a tetragonal and monoclinic phase is being reported for the first time. [ABSTRACT FROM AUTHOR]

We have demonstrated magnetodielectric (MD) coupling in an Ising-chain magnet Sr2Ca2CoMn2O9 via detailed investigation of ac susceptibility and dielectric constant as a function of temperature, magnetic field, and frequency. Sr2Ca2CoMn2O9 consists of spin-chains made of the regular stacking of one CoO6 trigonal prism with two MnO6 octahedra. The (Co2+–Mn4+–Mn4+) unit stabilizes a (↑↓↑) spin-state along the chains that are distributed on a triangular lattice. This compound undergoes a partially disordered antiferromagnetic transition at TN ∼ 28 K. The dielectric constant exhibits a clear peak at TN only in the presence of an external magnetic field (H ≥ 5 kOe), evidencing the presence of MD coupling, which is further confirmed by field-dependent dielectric measurements. We argue that spatial inversion symmetry can be broken as a result of exchange-striction along each spin chain, inducing uncompensated local dipoles. At low temperatures, a dipolar relaxation phenomenon is observed, bearing strong similarities to the blocking effect typical of spin dynamics in this compound. Such a spin-dipole relationship is referred to as a "multiblocking" effect, in relation to the concept of magnetodielectric "multiglass" previously introduced for related materials. [ABSTRACT FROM AUTHOR]

The effect of ion irradiation on the proximity effect in YBa2Cu3O7−δ/La0.67Sr0.33MnO3 and YBa2Cu3O7−δ/SrTiO3/La0.67Sr0.33MnO3 heterostructures has been investigated using spin-polarized neutron reflectivity experiments. We demonstrate that the magnetization in the ferromagnetic (La0.67Sr0.33MnO3) layer at the interface is correlated with the suppression of the superconductivity in the YBa2Cu3O7−δ layer after irradiation, while the layer structure of the heterostructures remains intact. The evolution of the magnetization of the interfacial ferromagnetic layer studied as a function of temperature for both the irradiated heterostructures shows the absence of the proximity effect observed in the un-irradiated samples. The absence of a proximity effect is attributed to the suppression of the superconductivity, as seen in macroscopic magnetization measurements of the heterostructures after ion irradiation. [ABSTRACT FROM AUTHOR]

Antiferromagnetic coupling between rare-earth (RE) and transition metals (TM) gives rise to various magnetic ground states in RE/TM heterostructures. Interface structure and morphology tend to play important roles in defining the magnetic properties of heterostructures of these materials. Using spin-dependent polarized neutron reflectivity (PNR), we found a distinct magnetic structure for RE/TM (Gd/Co) multilayers having different interface morphologies. Two Gd/Co multilayers, each consisting of eight bilayers of Gd and Co, were grown at different argon pressures to accomplish variation in the interface morphology. The Gd/Co multilayer, which is grown at a lower argon pressure, exhibits lower intermixing/interdiffusion at the interfaces and shows asymmetric magnetic hysteresis loops below the compensation temperature (Tcomp ∼ 140 K) and antisymmetric magnetoresistance at Tcomp. The other multilayer, grown at two different argon pressures for the top and bottom four bilayers, shows a double hysteresis loop with an exchange-bias-like shift to the field axis at temperatures above Tcomp (∼150 K). From PNR measurements across Tcomp, these behaviors were attributed to interface dependent magnetic helical structures. The PNR results indicate the formation of a twisted helical magnetic structure with planar 2π domain walls and the evolution of magnetic inhomogeneities below Tcomp. The interface dependent twisted helical magnetic structures and the development of highly correlated magnetic inhomogeneities may find applications in all-spin-based technologies. [ABSTRACT FROM AUTHOR]

Exploring the behavior of hydrocarbon under pressure is important for understanding its role in planetary sciences and also for exploring novel organic chemistry. In this study, we explored the high-pressure behavior of a linear-chain hydrocarbon, tricosane (C23H48), using Raman spectroscopy. We compressed tricosane up to 23 GPa and did not find any evidence for pressure-induced amorphization within the conditions explored in this study. Upon compression, we observe new modes in the low energy region 100–300 cm−1. In order to understand the appearance of these new modes at high pressures, we used complementary ab initio calculations and explored the effect of chain configurations (linear and bent) on the predicted Raman spectra. We find that these new modes observed at higher pressures are better explained by bent configuration of tricosane chains. Thus, based on high-pressure Raman spectra, it is very likely that a linear chain of tricosane is bent under pressure, i.e., it undergoes a pressure-induced trans-gauche transformation. It is also likely that such bent regions (i.e., kinks) will act as sites along which large chain hydrocarbons could dissociate into smaller chain lengths at extreme conditions relevant to the interiors of Jovian planets. [ABSTRACT FROM AUTHOR]

We have deposited LaNiO3 thin films on LaAlO3 (001), SrTiO3 (001), and Si (001) substrates using the pulsed laser deposition technique. Depositions were carried out at various substrate temperatures ranging from 0 to 800 °C. The effects of lattice mismatch and structural disorder on the transport properties of films deposited on various substrates and at different substrate temperatures are reported. X-ray diffraction confirms a highly c-axis oriented growth of LaNiO3 films on all the substrates at substrate temperatures of 600 and 800 °C, while at lower substrate temperatures deposited films are amorphous. Emergence of a new Raman mode indicates symmetry lowering in all the deposited crystalline films. Hardening of the Eg(3) (∼400 cm−1) mode is also observed with the rise of in-plane compressive strain. Resistivity curves for films on Si show a semiconducting behaviour and follow a variable range hopping mechanism. Crystalline films on LaAlO3 and SrTiO3 exhibit a metallic character along with a low-temperature resistivity upturn, which is attributed to the contribution of self-localization to resistivity at low temperatures as indicated by magnetotransport measurements. [ABSTRACT FROM AUTHOR]

Vanadium is a transition metal with multiple oxidation states and V2O5 is the most stable form among them. Besides catalysis, chemical sensing, and photo-chromatic applications, V2O5 is also reported to exhibit a semiconductor to metal transition (SMT) at a temperature range of 530–560 K. Even though there are debates in using the term “SMT” for V2O5, the metallic behavior above the transition temperature and its origin are of great interest in the scientific community. In this study, V2O5 nanostructures were deposited on a SiO2/Si substrate by the vapour transport method using Au as a catalyst. Temperature dependent electrical measurement confirms the SMT in V2O5 without any structural change. Temperature dependent photoluminescence analysis proves the appearance of oxygen vacancy related peaks due to reduction of V2O5 above the transition temperature, as also inferred from temperature dependent Raman spectroscopic studies. The newly evolved defect levels in the V2O5 electronic structure with increasing temperature are also understood from the downward shift of the bottom most split-off conduction bands due to breakdown of pdπ bonds leading to metallic behavior in V2O5 above the transition temperature. [ABSTRACT FROM AUTHOR]

The analysis of the structure of a Fe/Ge multilayer formed by rf sputtering on Si(100) substrate is done and its microscopic and macroscopic magnetic properties are characterized. It is observed that the Fe layer is polycrystalline in structure while the Ge layer has an amorphous structure.

This paper reports a new low cost technique for fabricating Surface Enhanced Raman Spectroscopy substrates. A Gold (Au) nano-metallic structure for surface enhancement is created by depositing Au nanoparticles on a Multi-wall Carbon Nanotube layer previously deposited on the etched Aluminum foil. A low cost, simple method is used to deposit the nanotubes. Huge enhancements have been observed in both in vitro and in vivo measurements. [ABSTRACT FROM AUTHOR]

The field-effect mobility characteristics of a non-degenerate ensemble of a two dimensional electron gas for interaction with acoustic mode lattice vibrations in the Si-SiO2 MOS structure at the high surface electric fields are calculated here for the low and high temperature cases. The calculation takes due account of some features which are usually neglected. These include the effects of (i) the transverse component of the phonon wave vector, (ii) the realistic model of the infinite triangular potential well along the transverse direction, while applying the momentum conservation approximation, and (iii) the full form of the phonon distribution function at low temperatures. The results seem to be interesting in that they are significantly different from what follows from other theories that neglect the effects of the above features. Moreover, the agreement between the results which are obtained here with the experimental data seems to be significantly better. The scope for further refinement of the present theory has been discussed. [ABSTRACT FROM AUTHOR]

Publisher's Note: "Crystal structure determination of a new monoclinic phase in NiMn system in a self-assembled chessboard-like microstructure" [J. Appl. Phys. The equation is correct as it appears below. This article was originally published online on 26 April 2023 missing the first displayed equation on page 5. [Extracted from the article]

Cu2O nanoparticles of diameter in the range 6-8.6 nm are synthesized by a chemical method. The results indicate that the interfacial amorphous phase of the nanoparticle assembly controls the electrical properties of the system.

An investigation of the acoustic velocity and acoustic attenuation of lead-vanadate glasses has been conducted. The study used ultrasonic methodology in temperatures ranging from 80 to 300 degrees Kelvin. The observed temperature dependence in attenuation can be rationalized in terms of relaxation process that is activated thermally while the velocity variation is attributed to the microscopic inhomogeneity of elasticity in glasses that is caused by anharmonicity, relaxation and frozen-in fluctuations.

Research was conducted to examine the fluctuation induced conductivity (FIC) of two high critical temperature superconductors (HTSC) namely Bi2Sr2Ca1O(sub 8+infinity) and Y(sub 1-x)Ca(sub x)Ba2Cu3O(sub y). An evaluation of the FIC was carried out as well as a comparison with the theoretically derived values from the proposed model. Results show that both the HTSC materials studied have similar behavior concerning the crossover which is revealed with the different extents of the fluctuations regions.

Research was conducted to examine the dynamics of grain growth and the pinning effect of grain boundaries on magnetic domain walls in FeCo soft magnetic alloys. Grain growth was observed to occur at temperatures above 600 degrees C. By keeping the same ordering parameter for all samples investigated, the effect of grain size on magnetic properties was determined. Results also demonstrate that grain boundaries serve as pinning sites for the magnetic domain wall movement.

A crystallographic model was developed to represent epitaxy of GaN on (1120) sapphire. The (1102) cleavage plane in sapphire was found to extend to the GaN lattice as the (1120) plane, encouraging the formation of cleaved facets. Even though the lattice mismatch is much smaller than in the case of epitaxy on (0001), the difference in the planar symmetry produced high-strained bonds near the interface.

We have obtained the expressions for the terminal currents in a heterojunction bipolar transistor laser the base of which contains a quantum well (QW). The emitter-base junction is assumed to be abrupt, leading to abrupt discontinuity in quasi-Fermi level at the interface. The expressions for the terminal currents as a function of collector-emitter and base-emitter voltages are obtained from the solution of the continuity equation. The current density in the QW located at an arbitrary position in the base is related to the virtual state current density. The threshold current density in the QW is calculated by using the expression for gain obtained from Fermi golden rule. The plot of collector current (IC) versus collector-emitter voltage (VCE) for different values of base current shows the usual transistor characteristics, i.e., a rising portion after a cut-in VCE, and then a saturation behavior. The dc current gain remains constant. However, as the base current exceeds the threshold, a stimulated recombination rate is added to the spontaneous recombination rate and the plots of collector currents become closer for the same increase in base current. This current gain compression is in agreement with the experimental observation. Our calculated values qualitatively agree with other experimental findings; however some features like Early effect do not show up in the calculation. [ABSTRACT FROM AUTHOR]

A study was conducted to analyze long range atomic ordering in InGaN films prepared by molecular beam epitaxy on A-plan sapphire. The films were prepared using a three-step process. The sapphire substrates were nitridated by exposing their surface to an electron cyclotron resonance nitrogen plasma at 800 degrees C. X-ray diffraction experiments were carried out on a four-circle, double crystal diffractometer. Experimental results indicated that the degree of ordering correlated with increases in growth rate.

A small quantity of carbon nanotubes (CNTs) was dispersed in a liquid crystal (LC) and the LC+CNT hybrid in the isotropic phase was found to exhibit an insulator-to-conductor transition when an external electric field was applied. This effect was probed by measuring the resistance of the system as a function of applied voltage across the LC cell. In an LC+CNT hybrid, the LC molecules self-assemble themselves at the CNT surface due to π-π electron stacking, creating pseudonematic domains (PNDs) surrounding the CNTs. These CNT-embedded PNDs interact with the external electric field even in the isotropic phase of the LC. When the external field is applied, the PND-encapsulated CNTs start to rotate along the field and form wires due to their natural tendency of entanglement. The CNT-wires eventually short the two electrodes of the LC cell, manifesting an insulator-to-conductor transition in the LC+CNT hybrid. Additional studies revealed that the cell spacing and the CNT-concentration had a significant impact on the threshold voltage across the LC cell for the insulator-to-conductor transition process. [ABSTRACT FROM AUTHOR]

Recently, near-field thermal radiation has attracted much attention in several fields since it can exceed the Planck blackbody limit through the coupling of evanescent waves. In this work, near-field radiative heat transfer between two semi-infinite dual uniaxial electromagnetic metamaterials with two different material property sets is theoretically analyzed. The near-field radiative heat transfer is calculated using fluctuational electrodynamics incorporated with anisotropic wave optics. The underlying mechanisms, namely, magnetic hyperbolic mode, magnetic surface polariton, electrical hyperbolic mode, and electrical surface polariton, between two homogeneous dual uniaxial electromagnetic metamaterials are investigated by examining the transmission coefficient and the spectral heat flux. The effect of vacuum gap distance is also studied, which shows that the enhancement at smaller vacuum gap is mainly due to hyperbolic mode and surface plasmon polariton modes. In addition, the results show that the contribution of s-polarized waves is significant and should not be excluded due to the strong magnetic response regardless of vacuum gap distances. The fundamental understanding and insights obtained here will facilitate the finding and application of novel materials for near-field thermal radiation. [ABSTRACT FROM AUTHOR]

The in-plane switching (IPS) for a nematic liquid crystal (LC) was found to be considerably faster when the LC was doped with dilute concentrations of monolayer graphene flakes. Additional studies revealed that the presence of graphene reduced the rotational viscosity of the LC, permitting the nematic director to respond quicker in IPS mode on turning the electric field on. The studies were carried out with several graphene concentrations in the LC, and the experimental results coherently suggest that there exists an optimal concentration of graphene, allowing a reduction in the IPS response time and rotational viscosity in the LC. Above this optimal graphene concentration, the rotational viscosity was found to increase, and consequently, the LC no longer switched faster in IPS mode. The presence of graphene suspension was also found to decrease the LC's pretilt angle significantly due to the π-π electron stacking between the LC molecules and graphene flakes. To understand the π-π stacking interaction, the anchoring mechanism of the LC on a CVD grown monolayer graphene film on copper substrate was studied by reflected crossed polarized microscopy. Optical microphotographs revealed that the LC alignment direction depended on monolayer graphene's hexagonal crystal structure and its orientation. [ABSTRACT FROM AUTHOR]

Research was conducted to measure the velocity and attenuation of longitudinal and transverse ultrasonic waves in PbO-V2O5-P2O5 glass systems. Experiments were performed at temperatures ranging from 80 to 300 K using the ultrasonic pulse echo overlap method at 10 MHz. Results demonstrate that the velocities decreased steadily and slowly with increasing temperature. The variation of velocity with temperature is explained by the combination of anharmonicity, relaxation and frozen-in fluctuation.

A study was conducted to elucidate the long-range atomic ordering and phase separation processes in InGaN alloys grown by molecular beam epitaxy. Results revealed that films produced at substrate temperatures from 700 to 750 degrees C with indium concentration greater than 35% exhibit phase separation. Moreover, films produced at substrate temperatures from 650 up to 675 degrees C showed compositional inhomogeneity when the indium content was higher than 25%.

An analysis of the association between the electrical properties and microstructure of YBa2Cu3O(7-x) thin films established a quantitative relation between substrate temperature and critical temperature (TC), normal-state resistivity rho, JC, orientation patterns, X-ray diffraction peak width, lattice width, microwave surface resistance and penetration depth lambda. A rise in substrate temperature to an enhanced TC and a decline in rho value increased JC value and grainsize. It also increased the ratio of c-axis- to a-axis oriented grains.

In this paper, based on piezoforce measurements, we show the presence of opposite polarization at grains and grain boundaries of Al-doped ZnO (AZO). The polarization can be flipped by 180° in phase by switching the polarity of the applied electric field, revealing the existence of nanoscale pseudoferroelectricity in AZO grown on Pt/TiO2/SiO2/Si substrate. We also demonstrate an experimental evidence on local band bending at grain boundaries of AZO films using conductive atomic force microscopy and Kelvin probe force microscopy. The presence of an opposite polarization at grains and grain boundaries gives rise to a polarization-driven barrier formation at grain boundaries. With the help of conductive atomic force microscopy, we show that the polarization-driven barrier along with the defect-induced electrostatic potential barrier account for the measured local band bending at grain boundaries. The present study opens a new avenue to understand the charge transport in light of both polarization and electrostatic effects. [ABSTRACT FROM AUTHOR]

A study was done to determine the processing conditions required for the initiation of liquid metal expulsion during pulsed laser irradiation using experimental and theoretical models. Results from pulsed irradiation of lead, titanium and stainless steel samples show that conditions for the initiation of liquid metal expulsion can be demonstrated from theoretically computed transient spatial temperature profiles and balancing of surface tension and recoil forces.

We have carried out dc magnetization, heat-capacity, and dielectric studies down to 2K for the compound GdCrTiO5, crystallizing in orthorhombic Pbam structure, in which well-known multiferroics RMn2O5 (R=Rare-earths) form. The points of emphasis are: (i) The magnetic ordering temperature of Cr appears to be suppressed compared with that in isostructural Nd counterpart, NdCrTiO5. This finding on the Gd compound suggests that Nd 4f hybridization plays an uncommon role in the magnetism of Cr in contrast to a proposal long ago. (ii) Dielectric constant does not exhibit any notable feature below about 30K in the absence of external magnetic field, but a peak appears and gets stronger with the application of external magnetic fields, supporting the existence of magnetodielectric coupling. (iii) The dielectric anomalies appear even near 100 K, which can be attributed to short-range magnetic-order. We also observe a gain in spectral weight below about 150K in Raman spectra in the frequency range 150-400 cm-1, which could be magnetic in origin, supporting short-range magnetic order. It is of interest to explore whether geometrically frustration plays any role in the dielectric properties of this family, as in the case of RMn2O5. [ABSTRACT FROM AUTHOR]

We have carried out dc magnetization, heat-capacity, and dielectric studies down to 2K for the compound GdCrTiO5, crystallizing in orthorhombic Pbam structure, in which well-known multiferroics RMn2O5 (R=Rare-earths) form. The points of emphasis are: (i) The magnetic ordering temperature of Cr appears to be suppressed compared with that in isostructural Nd counterpart, NdCrTiO5. This finding on the Gd compound suggests that Nd 4f hybridization plays an uncommon role in the magnetism of Cr in contrast to a proposal long ago. (ii) Dielectric constant does not exhibit any notable feature below about 30K in the absence of external magnetic field, but a peak appears and gets stronger with the application of external magnetic fields, supporting the existence of magnetodielectric coupling. (iii) The dielectric anomalies appear even near 100 K, which can be attributed to short-range magnetic-order. We also observe a gain in spectral weight below about 150K in Raman spectra in the frequency range 150-400 cm-1, which could be magnetic in origin, supporting short-range magnetic order. It is of interest to explore whether geometrically frustration plays any role in the dielectric properties of this family, as in the case of RMn2O5. [ABSTRACT FROM AUTHOR]

Monolayer graphene flakes were dispersed at low concentrations into two achiral liquid crystals (LCs) alkoxyphenylbenzoate (9OO4) and 4-cyano-4'-pentylbiphenyl (5CB), separately. The presence of graphene resulted in two types of chiral signatures in the LCs: an electroclinic effect (a polar tilt of the LC director perpendicular to, and linear in, an applied electric field) in the smectic-A phase of 9OO4, and a macroscopic helical twist of the LC director in the nematic phase of 5CB. Graphene flakes generally possess strain chirality and edge chirality. The non-covalent interactions between the LC molecules and chiral graphene flakes induce molecular conformational deracemization in the LC, exhibiting a bulk electroclinic effect and a macroscopic helical twist. [ABSTRACT FROM AUTHOR]

Al-doped ZnO (AZO) thin films of thicknesses 5,10, 15, 20, and 30 nm were deposited on 500 eV argon ion-beam fabricated nanoscale self-organized rippled-Si substrates at room temperature and are compared with similar films deposited on pristine-Si substrates (without ripples). It is observed that morphology of self-organized AZO films is driven by the underlying substrate morphology. For instance, for pristine-Si substrates, a granular morphology evolves for all AZO films. On the other hand, for rippled-Si substrates, morphologies having chain-like arrangement (anisotropic in nature) are observed up to a thickness of 20 nm, while a granular morphology evolves (isotropic in nature) for 30 nm-thick film. Photoluminescence studies reveal that excitonic peaks corresponding to 5-15 nm-thick AZO films, grown on rippled-Si templates, show a blue shift of 8 nm and 3 nm, respectively, whereas the peak shift is negligible for 20-nm thick film (with respect to their pristine counter parts). The observed blue shifts are substantiated by diffuse reflectance study and attributed to quantum confinement effect, associated with the size of the AZO grains and their spatial arrangements driven by the anisotropic morphology of underlying rippled-Si templates. The present findings will be useful for making tunable AZO-based light-emitting devices. [ABSTRACT FROM AUTHOR]

A technique is presented to produce any desired partially coherent Schell-model source using a single phase-only liquid-crystal spatial light modulator (SLM). Existing methods use SLMs in combination with amplitude filters to manipulate the phase and amplitude of an initially coherent source. The technique presented here controls both the phase and amplitude using a single SLM, thereby making the amplitude filters unnecessary. This simplifies the optical setup and significantly increases the utility and flexibility of the resulting system. The analytical development of the technique is presented and discussed. To validate the proposed approach, experimental results of three partially coherent Schell-model sources are presented and analyzed. A brief discussion of possible applications is provided in closing. [ABSTRACT FROM AUTHOR]

High sensitivity gas sensors are typically realized using metal catalysts and nanostructured materials, utilizing non-conventional synthesis and processing techniques, incompatible with on-chip integration of sensor arrays. In this work, we report a new device architecture, suspended core-shell Pt-PtOx nanostructure that is fully CMOS-compatible. The device consists of a metal gate core, embedded within a partially suspended semiconductor shell with source and drain contacts in the anchored region. The reduced work function in suspended region, coupled with built-in electric field of metal-semiconductor junction, enables the modulation of drain current, due to room temperature Redox reactions on exposure to gas. The device architecture is validated using Pt-PtO2 suspended nanostructure for sensing H2 down to 200 ppb under room temperature. By exploiting catalytic activity of PtO2, in conjunction with its p-type semiconducting behavior, we demonstrate about two orders of magnitude improvement in sensitivity and limit of detection, compared to the sensors reported in recent literature. Pt thin film, deposited on SiO2, is lithographically patterned and converted into suspended Pt-PtO2 sensor, in a single step isotropic SiO2 etching. An optimum design space for the sensor is elucidated with the initial Pt film thickness ranging between 10 nm and 30 nm, for low power (<5 μW), room temperature operation. [ABSTRACT FROM AUTHOR]

Using conductive atomic force microscopy and Kelvin probe force microscopy, we study local electrical transport properties in aluminum-doped zinc oxide (ZnO:Al or AZO) thin films. Current mapping shows a spatial variation in conductivity which corroborates well with the local mapping of donor concentration (~1020cm-3). In addition, a strong enhancement in the local current at grains is observed after exposing the film to ultra-violet (UV) light which is attributed to persistent photocurrent. Further, it is shown that UV absorption gives a smooth conduction in AZO film which in turn gives rise to an improvement in the bulk photoresponsivity of an n-AZO/p-Si heterojunction diode. This finding is in contrast to the belief that UV absorption in an AZO layer leads to an optical loss for the underneath absorbing layer of a heterojunction solar cell. [ABSTRACT FROM AUTHOR]

We embarked on a study of Scandium (Sc) doped (onto Ga site) gallium ferrite (GaFeO3) and found remarkable magnetic properties. In both doped as well as parent compounds, there were three types of Fe3+ions (depending on the symmetry) with the structure conforming to space group Pna21 (Sp. Grp. No. 33) below room temperature down to 5 K. We also found that all Fe3+ions occupy octahedral sites, and carry high spin moment. For the higher Sc substituted sample (Ga1-xScxFeO3:x = 0.3), a canted magnetic ordered state is found. Spin-phonon coupling below Néel temperature was observed in doped compounds. Our results indicated that Sc doping in octahedral site modifies spin-phonon interactions of the parent compound. The spin-phonon coupling strength was estimated for the first time in these Sc substituted compounds. [ABSTRACT FROM AUTHOR]

A small quantity of graphene, containing both monolayer and multilayer flakes, was doped in a nematic liquid crystal (LC), and the nematic electro-optic switching was found to be significantly faster in the LC + graphene hybrid than that of the pure LC. Additional studies revealed that the presence of graphene reduced the free ion concentration in the nematic media by ion-trapping process. The reduction of mobile ions in the LC was found to have subsequent impacts on the LC's conductivity and rotational viscosity, allowing the nematic director to respond quicker on switching the electric field on and off. [ABSTRACT FROM AUTHOR]

We investigate near-field radiative heat transfer between Indium Tin Oxide (ITO) nanowire arrays which behave as type 1 and 2 hyperbolic metamaterials. Using spatial dispersion dependent effective medium theory to model the dielectric function of the nanowires, the impact of filling fraction on the heat transfer is analyzed. Depending on the filling fraction, it is possible to achieve both types of hyperbolic modes. At 150 nm vacuum gap, the heat transfer between the nanowires with 0.5 filling fraction can be 11 times higher than that between two bulk ITOs. For vacuum gaps less than 150 nm the heat transfer increases as the filling fraction decreases. Results obtained from this study will facilitate applications of ITO nanowires as hyperbolic metamaterials for energy systems. [ABSTRACT FROM AUTHOR]

High pressure Raman spectroscopy, X-ray diffraction, and dielectric measurements have been carried out in Ba1-xSrxTiO3 (x=0.05 and 0.1). Detailed structural analysis revealed a single phase transition from tetragonal P4mm to cubic Pm3m symmetry. Increase in Sr ion concentration resulted in decrease in the phase transition pressure. The dielectric measurements showed considerable lowering of transition pressure which has been attributed to bulk behaviour of the material. [ABSTRACT FROM AUTHOR]

High pressure Raman spectroscopy, X-ray diffraction, and dielectric measurements have been carried out in Ba1-xSrxTiO3 (x=0.05 and 0.1). Detailed structural analysis revealed a single phase transition from tetragonal P4mm to cubic Pm3m symmetry. Increase in Sr ion concentration resulted in decrease in the phase transition pressure. The dielectric measurements showed considerable lowering of transition pressure which has been attributed to bulk behaviour of the material. [ABSTRACT FROM AUTHOR]

Ni-aluminides are an important class of intermetallics from technological point of view. Ni-Al phase diagram has been studied in detail experimentally as well as theoretically. It is known that if annealed at low temperature, the first alloy phase is usually NiAl3 according to Bené's rule. It is also understood that heat of formation may get modified by local densities of the constituents forming the alloy. In this regard, it is important to identify a kinetic length scale for defining "local density" in a system. We have deposited ultrathin multilayers of Ni and Al of layer thickness in tens of nanometres with Ni:Al stoichiometric ratio as 3:1 and 1:3, respectively. Considering these stoichiometry, Ni3Al and NiAl3 are the thermodynamically favoured alloy phases in these samples. We used x-ray reflectivity, polarized neutron reflectivity, x-ray diffraction, and secondary ion mass spectroscopy to follow the alloy formation after annealing and identified the alloy phases at interfaces with nanometre resolution. Diffusion length of Ni and Al was obtained using Darken's law. Our results predict that 'diffusion length' is the unique length scale that connects kinetics to local density. In another interesting observation, using "virtual Kirkendall markers" at the interfaces, we showed asymmetry in consumption of Al for alloy formation, at Al on Ni (Al/Ni) and Ni on Al (Ni/Al) interfaces by comparing as-deposited and annealed states with respect to the markers. [ABSTRACT FROM AUTHOR]

Dispersion of nanoparticles in polymer nanocomposite films determines the application potential of these systems as novel materials with unique physical properties. Grafting polymers to, mostly inorganic, nanoparticles has been suggested as an effective strategy to enhance dispersion and hence the efficacy of materials. In this review, we discuss the various parameters which control dispersion of polymer grafted nanoparticles in polymer nanocomposite films. We discuss how surface x-ray scattering and microscopy can provide complementary and unique information in thin polymer nanocomposite films to unravel the subtle interplay of entropic and surface interactions, mediated by confinement, that leads to enhanced dispersion of the nanoparticles in these films. [ABSTRACT FROM AUTHOR]

In this paper, a fluence-dependent antireflection performance is presented from ion-beam fabricated nanofaceted-Si surfaces. It is also demonstrated that these nanofacets are capable of producing room temperature ultra-violet and blue photoluminescence which can be attributed to inter-band transitions of the localized excitonic states of different Si-O bonds at the Si/SiOx interface. Timeresolved photoluminescence measurements further confirm defect-induced radiative emission from the surface of silicon nanofacets. It is observed that the spectral characteristics remain unchanged, except an enhancement in the photoluminescence intensity with increasing ion-fluence. The increase in photoluminescence intensity by orders of magnitude stronger than that of a planar Si substrate is due to higher absorption of incident photons by nanofaceted structures. [ABSTRACT FROM AUTHOR]

We have recently reported that the Haldane spin-chain system, Er2BaNiO5, undergoing antiferromagnetic order below (TN=) 32K, is characterized by the onset of ferroelectricity near 60K due to magnetoelectric coupling induced by short-range magnetic-order within spin-chains. We have carried out additional magnetic and dielectric studies to understand the properties well below TN. We emphasize here on the following: (i) A strong frequency dependent behaviors of ac magnetic susceptibility and complex dielectric properties have been observed at much lower temperatures (<8 K), that is, "reentrant multiglass-like" phenomenon, naturally suggesting the existence of an additional transition well below TN. (ii) "Magnetoelectric phase coexistence" is observed at very low temperature (e.g., T=2 K), where the high-field magnetoelectric phase is partially arrested on returning to zero magnetic field after a cycling through metamagnetic transition. [ABSTRACT FROM AUTHOR]

We report the observation of electric polarization in the magnetically ordered state of the Haldane chain compound, Gd2BaNiO5, with strongly correlated magnetic and dielectric properties. The results of dc magnetic susceptibility and heat capacity measurements indicate two magnetic transitions, one corresponding to the anti-ferromagnetic order at TN~55K and the other to spin-reorientation transition at TSR~24 K. The dielectric permittivity ϵ'r and loss (tanδ) also exhibit anomalies in the vicinity of TSR and TN, respectively. Below the spin-reorientation transition, concurrently magnetic-field-induced spin-flop and the meta-electric transitions are observed at a critical magnetic field in isothermal magnetization and magneto-dielectric results, respectively. Another interesting finding is that Δϵ'r (=(ϵ'(H) - ϵ'(0))/ϵ'(0)) changes its sign at the critical magnetic field. The origin of the observed magneto-electric effect is discussed on the basis of spin-phonon coupling. [ABSTRACT FROM AUTHOR]

We report the observation of electric polarization in the magnetically ordered state of the Haldane chain compound, Gd2BaNiO5, with strongly correlated magnetic and dielectric properties. The results of dc magnetic susceptibility and heat capacity measurements indicate two magnetic transitions, one corresponding to the anti-ferromagnetic order at TN~55K and the other to spin-reorientation transition at TSR~24 K. The dielectric permittivity ϵ'r and loss (tanδ) also exhibit anomalies in the vicinity of TSR and TN, respectively. Below the spin-reorientation transition, concurrently magnetic-field-induced spin-flop and the meta-electric transitions are observed at a critical magnetic field in isothermal magnetization and magneto-dielectric results, respectively. Another interesting finding is that Δϵ'r (=(ϵ'(H) - ϵ'(0))/ϵ'(0)) changes its sign at the critical magnetic field. The origin of the observed magneto-electric effect is discussed on the basis of spin-phonon coupling. [ABSTRACT FROM AUTHOR]

Soft magnetic composites are fabricated by electrodepositing FeNi and FeCo onto W fibers with a diameter of 20 and 100 (mu)m. Magnetic measurements show that as-deposited fibers are not magnetically soft, after proper thermal annealing, the samples exhibit excellent soft magnetic properties.

The correlations between the magnetic properties and microstructure features of Fe49Co48.7V2Nb0.3 alloys are studied. It is shown that an increase in the structural ordering parameter determined by neutron diffraction decreases the coercive field. Lorentz microscopy results also show that the second phases and the grain boundaries function as spinning sites for the magnetic domain wall movement, which increase the coercive field.