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The phenomenon of exchange bias has been extensively studied within crystalline materials, encompassing a broad spectrum from nanoparticles to thin-film systems. Nonetheless, exchange bias in amorphous alloys has remained a relatively unexplored domain, primarily owing to their inherently uniform disordered atomic structure and lacking grain boundaries. In this study, we present a unique instance of exchange bias observed in Fe–B–Nb amorphous thin films, offering insights into its origins intertwined with the system's spin-glass-like behavior at lower temperatures. The quantification of exchange bias was accomplished through a meticulous analysis of magnetic reversal behaviors in the liquid-helium temperature range, employing a zero-field cooling approach from various initial remanent magnetization states (±MR). At reduced temperatures, the appearance of asymmetric hysteresis, a hallmark of negative exchange bias, undergoes a transformation into symmetric hysteresis loops at elevated temperatures, underscoring the intimate connection between exchange-bias and dynamic magnetic states. Further investigations into the magnetic thermal evolution under varying probe fields reveal the system's transition into a spin-glass-like state at low temperatures. We attribute the origin of this unconventional exchange bias to the intricate exchange interactions within the spin-glass-like regions that manifest at the interfaces among highly disordered Fe-nuclei. The formation of Fe-nuclei agglomerates at the sub-nanometer scale is attributed to the alloy's limited glass-forming ability and the nature of the thin-film fabrication process. We propose that this distinctive form of exchange bias represents a novel characteristic of amorphous thin films. [ABSTRACT FROM AUTHOR]

The increase in the global demand for plastics, and more recently during the pandemic, is a major concern for the future of plastic waste pollution and microplastics. Efficient microplastic monitoring is imperative to understanding the long-term effects and progression of microplastic effects in the environment. Numerical models are valuable in studying microplastic transport as they can be used to examine the effects of different parameters systematically to help elucidate the fate and transport processes of microplastics, thus providing a holistic view of microplastics in the ocean environment. By incorporating physical parameters (such as size, shape, density, and identity of microplastics), numerical models have gained better understanding of the physics of microplastic transport, predicted sinking velocities more accurately, and estimated microplastic pathways in marine environments. However, availability of large amounts of information about microplastic physical and chemical parameters is sparse. Machine learning and computer-vision tools can aid in acquiring environmental information and provide input to develop more accurate models and verify their predictions. More accurate models can further the understanding of microplastic transport, facilitate monitoring efforts, and thus optimize where more data collection can take place to ultimately improve machine learning tools. This review offers a perspective on how image-based machine learning can be exploited to help uncover the physics of microplastic transport behaviors. Additionally, the authors hope the review inspires studies that can bridge the gap between numerical modeling and machine learning for microplastic analysis to exploit their joined potential. [ABSTRACT FROM AUTHOR]

The discovery of graphene and its fascinating capabilities has triggered an unprecedented interest in inorganic two-dimensional (2D) materials. van der Waals layered materials such as graphene, hexagonal boron nitride, transition metal dichalcogenides, and the more recently re-discovered black phosphorus (BP) indeed display an exceptional technological potential for engineering nano-electronic and nano-photonic devices and components "by design," offering a unique platform for developing new devices with a variety of "ad hoc" properties. In this Perspective article, we provide a vision on the key transformative applications of 2D nanomaterials for the development of nanoelectronic, nanophotonic, optical, and plasmonic devices at terahertz frequencies, highlighting how the rich physical phenomena enabled by their unique band structure engineering can allow them to boost the vibrant field of quantum science and quantum technologies. [ABSTRACT FROM AUTHOR]

This study deals with the design of a suitable configuration of jet deflector for supersonic exhaust gases from a semi-cryogenic launch vehicle engine using computational fluid dynamics. Computational model of combustion in semi-cryogenic engine, with kerosene as fuel and liquid oxygen as oxidizer, was developed in which exhaust gases from engine were impinged on the deflector surface. Different design configurations of deflector structure, obtained by the combination of various impingement angles of 15°, 20°, 25°, 30°, and 45°, and different exit radii of 5000, 10 000, and 20 000 mm, were used in the developed computational models to analyze impingement, deflection, and associated flow properties of exhaust gases, such as acoustics, force on deflector imparted by jet, temperature, and Mach number of flow field. A new ablation model was developed based on Vieille's law to determine the amount of refractory material ablated from deflector structure for different configurations. The developed models of ablation, combustion, and flow impingement were also validated with existing literature. It was found that the configuration with 20° impingement angle and 10 000 mm exit radius had ablation, acoustics, force, and flow properties in desired limit. Furthermore, to find the optimum uplift angle for designing jet deflector, configurations with uplift angles of 0°, 5°, 15°, and 25° were studied using the computational models developed in the study. It was observed that the configuration with 20° impingement angle, 10 000 mm exit radius, and 15° uplift angle was best suited for impingement and deflection of exhaust jet from the specified semi-cryogenic engine. [ABSTRACT FROM AUTHOR]

Graphene, with its unique band structure, mechanical stability, and high charge mobility, holds great promise for next-generation electronics. Nevertheless, its zero bandgap challenges the control of current flow through electrical gating, consequently limiting its practical applications. Recent research indicates that atomic oxygen can oxidize epitaxial graphene in a vacuum without causing unwanted damage. In this study, we have investigated the effects of chemisorbed atomic oxygen on the electronic properties of epitaxial graphene using scanning tunneling microscopy (STM). Our findings reveal that oxygen atoms effectively modify the electronic states of graphene, resulting in a bandgap at its Dirac point. Furthermore, we demonstrate that it is possible to selectively induce desorption or hopping of oxygen atoms with atomic precision by applying appropriate bias sweeps with an STM tip. These results suggest the potential for atomic-scale tailoring of graphene oxide, enabling the development of graphene-based atomic-scale electronic devices. [ABSTRACT FROM AUTHOR]

In this study, Mn54Al46 thin ribbons composed of nanostructured ferromagnetic and antiferromagnetic phases were fabricated by a melt spinning method, and a tunable exchange bias field was obtained by precisely controlling the wheel speed and the cooling field. The x-ray diffraction result confirms the existence of the nanostructured Mn-poor ε phase. The pinned ferromagnetic Mn-poor ε phase coupled with the antiferromagnetic Mn-rich ε phase accounts for the exchange bias observed in the sample fabricated at a wheel speed of 65 m/s in which almost no τ phase is formed. Furthermore, the exchange bias field first increases and reaches the most significant reported value of 41 kOe in this system and then decreases with the increase in the cooling field, exhibiting an inversely proportional relationship with the magnetization. The decrease in the exchange bias field is believed to be related to the increased coupling thickness of the ferromagnetic phases with the increase in the cooling field. [ABSTRACT FROM AUTHOR]

Observations of lamellar like fringes in iron-carbon-filled vertically aligned carbon nanotubes (CNTs) produced by pyrolysis of ferrocene and rapid cooling methodologies (controlled quenching) have been investigated. The quantitative phase analysis of encapsulated Fe3C, γ-Fe, and α-Fe by X-ray diffraction reveals that controlling the phase-percentage leads to control of the crystal habit and of magnetic properties. Large coercivities and variable saturation magnetizations were observed. In addition, we reported a thorough study of the hysteresis behavior, the Barkhausen effect which has to be possibly associated with the formation of interfacial-defects in the crystal areas in contact with CNT layers. [ABSTRACT FROM AUTHOR]

The interaction between 2,20-bithiophene-5-carboxylic acid (PT2) sublimed under ultra-high vacuum conditions and anatase (101) and rutile (110) TiO2 single crystal surfaces is investigated by studying the electronic spectral density near the Fermi level with synchrotron-based spectroscopy. The experimental results are compared to density functional theory calculations of the isolated PT2 molecule and of the molecule adsorbed on an anatase TiO2 (101) cluster. The relative concentrations of Ti, C, and S atoms indicate that the adsorbed molecule remains intact upon deposition, which is typical of a Stranski-Krastanov growth mode. The analysis of the O1s spectrum suggests a predominant bidentate geometry of the adsorption with both rutile and anatase surfaces, as supported by previous theoretical simulations. It is also theoretically and experimentally demonstrated that the PT2 adsorption causes the appearance of new electronic states in the gap near the TiO2 valence band. A pinning effect of the LUMO level of the dye is also theoretically predicted. [ABSTRACT FROM AUTHOR]

The unique optoelectronic properties of single layer graphene (SLG) are ideal for the development of photonic devices across a broad range of frequencies from x rays to microwaves. In the terahertz (THz) frequency range (0.1–10 THz), this has led to the development of optical modulators, nonlinear sources, and photodetectors with state-of-the-art performances. A key challenge is the integration of SLG-based active elements with pre-existing technological platforms in a scalable way, while maintaining performance level unperturbed. Here, we report room temperature THz detectors made of large-area SLG, grown by chemical vapor deposition (CVD) and integrated in antenna-coupled field effect transistors. We selectively activate the photo-thermoelectric detection dynamics, and we employ different dielectric configurations of SLG on Al2O3 with and without large-area CVD hexagonal boron nitride capping to investigate their effect on SLG thermoelectric properties underpinning photodetection. With these scalable architectures, response times ∼5 ns and noise equivalent powers (NEPs) ∼1 nW Hz−1/2 are achieved under zero-bias operation. This shows the feasibility of scalable, large-area, layered material heterostructures for THz detection. [ABSTRACT FROM AUTHOR]

Microplastic (MP) pollution poses severe environmental problems. Developing effective imaging tools for the identification and analysis of MPs is a critical step to curtail their proliferation. Digital holographic imaging can record the morphological and refractive index information of such small plastic fragments, yet due to the heterogeneous sampling environments and variations in the MP shapes, traditional supervised learning methods are of limited use. In this work, we pioneer a zero-shot learning method that combines the holographic images with their semantic attributes to identify the MPs in heterogeneous samples, even if they have not appeared in the training dataset. It makes use of the attention mechanism for image feature extraction and the Kullback–Leibler divergence both to alleviate the domain shift problem and to guide the training of the mapping function. Experimental results demonstrate the effectiveness of our approach and the potential use in a wide variety of environmental pollution assessments. [ABSTRACT FROM AUTHOR]

In this study, we examined a technique for maximizing the wear resistance of a polyurethane film composited with plasma-treated carbon nanotubes (CNTs). In our previous work, we showed that adding plasma-treated CNTs enhanced the wear resistance of off-the-shelf polyurethane. Here, we also investigated the chemical reactions between polyurethane and plasma-treated CNTs. The result showed that plasma-treatment modified isocyanate groups on CNTs possibly react with polyols to form urethane. However, the off-the-shelf polyurethane was supposed to have limited polyols because urethane reactions were mostly finished. In the present study, we synthesized polyurethane ourselves in order to compare how the timing of synthesis of plasma-treated CNTs into polyurethane (either before or after urethane reactions occur) impacts resulting films. Five polyurethane films were prepared, including a film composited with plasma-treated CNTs synthesized before urethane reactions (in situ polymerized CNT-composite polyurethane film). A wear-resistance test was then conducted to evaluate the mechanical properties of the composite films. The results showed that the plasma-treated CNTs enhanced wear resistance by a factor of two. Next, we conducted a tensile test to examine how the wear resistance was enhanced in polyurethane films composited with plasma-treated CNTs. The tensile test showed that in situ polymerized plasma-treated CNTs significantly improved Young's modulus of CNT-composite polyurethane. These combined results suggested that plasma-treated CNTs should be composited into polyurethane before urethane reactions occur to maximize the wear resistance of composite polyurethane. [ABSTRACT FROM AUTHOR]

The characteristic emission features of a laser-produced plasma depend strongly on the laser fluence. We investigated the spatial and temporal dynamics of neutrals and ions in a femtosecond laser (800 nm, ~40 fs, Ti:Sapphire) induced copper plasma in vacuum using both optical emission spectroscopy (OES) and spectrally resolved two-dimensional (2D) imaging over a wide fluence range of 0.5-77.5 J/cm2. 2D fast gated monochromatic images showed a distinct plume splitting between the neutrals and ions, especially at moderate to higher fluence. OES studies at low to moderate laser fluence confirm intense neutral line emission over ion emission, whereas this trend changes at higher laser fluence with dominance of the latter. This evidences a clear change in the physical processes involved in the femtosecond laser-matter interaction at high input laser intensity. The obtained ion dynamics resulting from OES and spectrally resolved 2D imaging are compared with charged particle measurement employing Faraday cup and Langmuir probe; results showed good correlation. [ABSTRACT FROM AUTHOR]

The plume expansion dynamics strongly affects the growth and the chemistry of pulsed laser deposited thin films. The interaction with the background gas determines the kinetic energy of the species impinging on the substrate, their angular broadening, the plasma chemistry, and eventually the cations stoichiometric ratio in oxide films. Here, we exploit two-dimensional, spectrally resolved plume imaging to characterize the diverse effects of the oxygen background pressure on the expansion dynamics of La, Ga, and LaO species during pulsed laser deposition of LaGaO3. The propagation of the ablated species towards the substrate is studied for background oxygen pressures ranging from high vacuum up to ≈10-1 mbar. Our experimental results show specie-dependent effects of the background gas on the angular distribution of the precursors within the plume. These findings suggest that even in the presence of a stoichiometric ablation and of a globally stoichiometric plume, cations off-stoichiometry can take place in the forefront portion of the plume impinging on the substrate. We show that such effect can be compensated by a proper choice of process parameters. [ABSTRACT FROM AUTHOR]

In 1971, the U.S. National Aeronautics and Space Administration (NASA) published a seminal report—NASA SP-8072—which compiled the results of the early supersonic jet noise studies and provided methods to calculate the noise produced from launch vehicles. Fifty years later and despite known limitations, SP-8072 remains the foundation for much of the launch vehicle noise modeling today. This article reviews what has been learned about the physics of noise generation and radiation from free and impinging rocket plumes since the completion of SP-8072. State-of-the-art methods for the mitigation of launch vehicle noise are also reviewed. A discussion of launch vehicle noise modeling, from empirical to numerical and including reduced-order models of supersonic jets, points to promising approaches that can describe rocket noise characteristics not captured by SP-8072. [ABSTRACT FROM AUTHOR]

Diffusion-driven coarsening of droplets is a classical subject in statistical physics, yet coarsening kinetics in confined systems have received little attention. We report here on the coarsening of droplets in thin (50–200 nm) films of phase-separated barium borosilicate glasses. In this ultra-confined geometry where at most one droplet is observed within the film thickness, droplets grow like a power-law of time with an exponent about 0.17 significantly smaller than that of the one of Ostwald ripening (1 / 3) characteristic of bulk coarsening. We complement these experimental results with two-dimensional Cahn–Hilliard numerical simulations of diffusion, where a wider range of parameters can be varied. In simulations, we recover a slow coarsening behavior in ultra-confined geometry. We explain the anomalous scaling exponent of simulations by ultraconfined geometry, which imposes a different scaling with time of the radius of a droplet and the distance between droplets. In the experimental system, diffusive transport also becomes less efficient with time compared to the bulk case with an additional change of geometry compared to simulations. Flattening of droplets with time is indeed observed, which we attribute to strong variations of the diffusion coefficient with the local matrix composition. We finally propose a simple model assuming a spatial localization of the diffusion paths to account for this effect. [ABSTRACT FROM AUTHOR]

A metallic waveguide transmitarray antenna (MWTA) is proposed to attain dual-band multibeams with high gain in the terahertz (THz) range, which is realized by independently controlling the phases of the two bands with orthogonal polarizations simultaneously. The phase distribution of each polarization on the MWTA for attaining the corresponding multibeam radiation pattern is calculated by using the Gerchberg–Saxton algorithm based on Fresnel diffraction theory. Furthermore, the phase delay of each unit cell is adjusted by varying the waveguide dimension to achieve the corresponding phase distributions. As a proof of concept, a dual-band MWTA with a diameter of 48 mm is designed and simulated to transform plane waves into triple beams at 0.14 THz and dual beams at 0.1 THz, respectively. Their peak gains are ∼30 and ∼28 dBi and the aperture efficiencies are 67% and 56%, respectively. Their 1 dB gain bandwidths can reach 10 GHz (136.5–146.5 GHz) and 11 GHz (94.7–105.6 GHz), respectively. The measured far-field results agree well with the simulations. The proposed dual-band THz antennas are very promising for applications in wireless and satellite communications. [ABSTRACT FROM AUTHOR]

We report that a model dye, Re(CO)3(bypy)CO2H, aggregates into clusters on TiO2 nanoparticles regardless of our preparation conditions. Using two-dimensional infrared (2D IR) spectroscopy, we have identified characteristic frequencies of monomers, dimers, and trimers. A comparison of 2D IR spectra in solution versus those deposited on TiO2 shows that the propensity to dimerize in solution leads to higher dimer formation on TiO2, but that dimers are formed even if there are only monomers in solution. Aggregates cannot be washed off with standard protocols and are present even at submonolayer coverages. We observe cross peaks between aggregates of different sizes, primarily dimers and trimers, indicating that clusters consist of microdomains in close proximity. 2D IR spectroscopy is used to draw these conclusions from measurements of vibrational couplings, but if molecules are close enough to be vibrationally coupled, then they are also likely to be electronically coupled, which could alter charge transfer. [ABSTRACT FROM AUTHOR]

Commonly, the key players in anticancer therapies and, more specifically, antineoplastic drugs display poor water solubility and slow dissolution rates. As a consequence, they present low bioavailability, poor tissue distribution, and unfavorable pharmacokinetic profiles, limiting their use. To overcome these barriers and improve efficacy, various drug formulations and delivery strategies have been developed. For example, nanoparticles can be used as drug delivery vehicles and current research is encouraging. However, the intra-tumoral diffusion of functionalized nanovehicles remains to be achieved. In the present study, the anticancer drug paclitaxel was loaded into superparamagnetic nanoparticles and characterized. Novel in vitro experiments based on one or two layers of cells revealed important information about the conditions required to achieve efficient drug intra-tumoral diffusion, using these superparamagnetic nanovectors, once they have been localized by external magnetic fields. These studies indicated that ultralow concentrations of paclitaxel (i.e., tenths of ng/μl) significantly reduce the viability of neoplastic cells when they are delivered with control using these nanovectors. Moreover, we showed that a discontinuous application of a magnetic field promotes the localization of the nanoparticles in a targeted region and favors the subsequent dissemination of the nanoparticles between cellular layers. [ABSTRACT FROM AUTHOR]

In this paper, low-power and ultrafast all-optical tunable plasmon induced transparency in metal-dielectric-metal (MDM) waveguide side-coupled Fabry-Perot (FP) resonators system with nonlinear optical Kerr medium is investigated both analytically and numerically. High tunability in transparency window magnitude and phase responses is obtained when nonlinear optical Kerr material is embedded in the MDM waveguide. In order to reduce the pump intensity, traditional nonlinear optical Kerr material is replaced by graphene. A shift of 64 nm in the central wavelength of the transparency window is achieved when the FP resonators are covered with monolayer graphene with pump intensity increasing from 9.2 to 10 MW/cm2. An ultrafast response time of the order of 1 ps is reached because of ultrafast carrier relaxation dynamics of graphene. This work not only paves the way towards the realization of on-chip integrated nanophotonic devices but also opens the possibility of the construction of ultrahigh-speed information processing chips based on plasmonic circuits. [ABSTRACT FROM AUTHOR]

Supervised learning-based sound source localization (SSL) methods have been shown to achieve a promising localization accuracy in the past. In this paper, MTIT, SSL for indoors using Multi-Task learning and Image Translation network, an image translation-based deep neural networks (DNNs) framework for SSL is presented to predict the locations of sound sources with random positions in a continuous space. We extract and represent the spatial features of the sound signals as beam response at each direction which can indicate the chance of the source in each point of the room. We utilize the multi-task learning (MTL) based training framework. There are one encoder and two decoders in our DNN. The encoder aims to obtain a compressed representation of the input beamspectrum surfaces while the two decoders focus on two tasks in parallel. One decoder focuses on resolving the multipath caused by reverberation and the other decoder predicts the source location. Since these two decoders share the same encoder, by training these two decoders in parallel, the shared representations are refined. We comprehensively evaluate the localization performance of our method in the simulated data, measured impulse response and real recordings datasets and compare it with multiple signal classification, steered response power with phase transform, and a competing convolutional neural network approach. It turns out that MTIT can outperform all of the baseline methods in a dynamic environment and also can achieve a good generalization performance. [ABSTRACT FROM AUTHOR]

The dynamics of ions in ultrafast laser ablation of metals is studied over fluences ranging from the ablation threshold up to ≈75 J/cm2 by means of three well-established diagnostic techniques. Langmuir probe, Faraday cup, and spectrally resolved intensified charge coupled device imaging simultaneously monitored the ions produced during ultrafast laser ablation of a pure copper target with 800 nm, ≈50 fs, Ti: Sapphire laser pulses. The fluence dependence of ion yield is analyzed, resulting in the observance of three different regimes. The specific ion yield shows a maximum at about 4-5 J/cm2, followed by a gradual reduction and a transition to a high-fluence regime above ≈50 J/cm2. The fluence dependence of the copper ions angular distribution is also analyzed, observing a gradual increase in forward-peaking of Cu ions for fluences up to ≈10 J/cm2. A broader ion component is observed at larger angles for fluences larger than ≈10 J/cm2. Finally, an experimental characterization of the ionic angular distribution for several metallic targets (Mg, Al, Cr, Fe, Cu, and W) is carried out at a relatively high fluence of ≈66 J/cm2. Interestingly, the ion emission from the volatile metals shows a narrow, forward-peaked distribution, and a high peak ion yield compared to the refractory metals. Moreover, the width of ionic angular distributions presents a striking correlation with the peak ion yield. [ABSTRACT FROM AUTHOR]

Laser surface structuring of copper is induced by laser ablation with a femtosecond optical vortex beam generated via spin-to-orbital conversion of the angular momentum of light by using a q-plate. The variation of the produced surface structures is studied as a function of the number of pulses, N, and laser fluence, F. After the first laser pulse (N=1), the irradiated surface presents an annular region characterized by a corrugated morphology made by a rather complex network of nanometer-scale ridges, wrinkles, pores, and cavities. Increasing the number of pulses (21000) and a deep crater is formed. The nanostructure variation with the laser fluence, F, also evidences an interesting dependence, with a coarsening of the structure morphology as F increases. Our experimental findings demonstrate that direct femtosecond laser ablation with optical vortex beams produces interesting patterns not achievable by the more standard beams with a Gaussian intensity profile. They also suggest that appropriate tuning of the experimental conditions (F, N) can allow generating micro- and/or nano-structured surface for any specific application. [ABSTRACT FROM AUTHOR]

Magnetic properties of 16nm La0.45Sr0.55MnO3 nanoparticles exhibit superparamagnetic blocking at 160K with a ferromagnetic moment appearing in the antiferromagnetic state. The exchange interaction at the interface between canted ferromagnetic and antiferromagnetic regions within the nanoparticles leads to exchange bias, but the loop shift, coercivity, and remanence asymmetry all decrease strongly with increasing cooling field above 1 T unlike a conventional ferromagnetic/antiferromagnetic exchange bias system. The observations imply a magnetization process involving coalescence of canted ferromagnetic clusters with increasing field, which reduces the interface area with the antiferromagnetic matrix. [ABSTRACT FROM AUTHOR]

We report a magnetic study on nanostructured (Fe79Mn21)1-xCux (0.00⩽x⩽0.30) alloys using static magnetic measurements. The alloys are mainly composed by an antiferromagnetic fcc phase and a disordered region that displays a spin-glass-like behavior. The interplay between the antiferromagnetic and magnetically disordered phases establishes an exchange anisotropy that gives rise to a loop shift at temperatures below the freezing temperature of moments belonging to the disordered region. The loop shift is more noticeable as the Cu content increases, which also enhances the spin-glass-like features. Further, in the x=0.30 alloy the alignment imposed by applied magnetic fields higher than 4 kOe prevail over the configuration determined by the frustration mechanism that characterizes the spin glass-like phase. [ABSTRACT FROM AUTHOR]

We fabricated an optically transparent monopole antenna using graphene film and investigated the feasibility of the film as an electrode material for antennas. A low sheet resistance (80 Ω/sq) was attained by stacking the graphene films and carrier doping with an ionic liquid. The optical transmittance of the carrier-doped three-layer stacked graphene film was greater than 90%, enabling it to be embedded in highly transparent objects without altering their landscape. Using the monopole antenna structure with a metal ground plane, we measured the reflection and radiation characteristics of the graphene monopole antenna, excluding the contribution from the power feeding components. The radiation efficiency of the graphene monopole antenna, which was measured by the Wheeler cap method, was determined to be 52.5% at 9.8 GHz. Through the measurements of the graphene monopole antenna, we demonstrated that the carrier-doped three-layer stacked graphene film can be used as an electrode material for optically transparent antennas. [ABSTRACT FROM AUTHOR]

Ferromagnetic BiFeO3 nanocrystals of average size 11 nm were used to form nanocomposites (x)BiFeO3/(100 - x)NiO, x = 0, 20, 40, 50, 60, 80, and 100 by simple solvothermal process. The ferromagnetic BiFeO3 nanocrystals embedded in antiferromagnetic NiO nanostructures were confirmed from X-ray diffraction and transmission electron microscope studies. The modification of cycloidal spin structure of bulk BiFeO3 owing to reduction in particle size compared to its spin spiral wavelength (62 nm) results in ferromagnetic ordering in pure BiFeO3 nanocrystals. High Neel temperature (TN) of NiO leads to significant exchange bias effect across the BiFeO3/NiO interface at room temperature. A maximum exchange bias field of 123.5 Oe at 300K for x = 50 after field cooling at 7 kOe has been observed. The exchange bias coupling causes an enhancement of coercivity up to 235 Oe at 300 K. The observed exchange bias effect originates from the exchange coupling between the surface uncompensated spins of BiFeO3 nanocrystals and NiO nanostructures. [ABSTRACT FROM AUTHOR]

Exchange bias (EB) effect has been studied in a series of nanogranular systems of ferrimagnetic (FiM) NiFe2O4 nanoparticles embedded into antiferromagnetic (AFM) NiO matrix, synthesized by a phase pprecipitation method from diluted Ni(1-x)FexO3 (x = 0.09) oxides. For these systems, the crystalline size (DNFO) of NiFe2O4 ranging from ∼3 nm to ∼55 nm has been obtained with thermal treated at different temperatures from 550 °C to 1000 °C. Magnetization measurement shows that both exchange bias field (HEB) and vertical magnetization shifts (MShift) can be exhibited below 250 K after field cooling procedure. The HEB and MShift decrease monotonically with crystalline size, and their behavior strongly depend on the crystalline size of NiFe2O4 nanoparticles. Linear relationship between HEB and MShift is observed for systems with smaller sizes (DNFO ≤ 8 nm), reveals a straightforward correlation between them. This phenomenon is ascribed to the interfacial exchange coupling between FiM NiFe2O4 clusters and spin-glass-like (SGL) phases, where the frozen uncompensated spins in SGL phases play critical role of inducing EB effect. As DNFO is above 12 nm, the dependence of HEB on MShift deviates from the linear relationship, which is discussed in terms of the superimposed contribution from the exchange coupling between FiM NiFe2O4 core with the SGL phase, and the exchange coupling between FiM NiFe2O4 core and AFM NiO phases at the interfaces. [ABSTRACT FROM AUTHOR]

A graphene-based field-effect-transistor with asymmetric dual-grating gates was fabricated and characterized under excitation of terahertz radiation at two frequencies: 0.15 THz and 0.3 THz. The graphene sheet was encapsulated between two flakes of h-BN and placed on a highly doped SiO2/Si substrate. An asymmetric dual-grating gate was implemented on the h-BN top flake. Even though no antenna was used to couple the incoming radiation, a clear gate-bias-dependent photocurrent was measured under excitation at 0.3 THz up to room temperature. We subsequently demonstrated that the device can be used for terahertz sensing and inspection of hidden metallic objects at room temperature. [ABSTRACT FROM AUTHOR]

Cyphochilus white beetles possess an exceptional ability to scatter visible light from their scales, which have anisotropic nanofibrillar network structures. We discover a striking effect that diffusely incident light on the beetle scales is preferentially channeled sideways and scattered backward on the average after traversing a vertical distance corresponding to only two scattering events. For normally incident light, the scattering is only slightly forward, resulting in close proximity between two optical characteristic lengths: scattering mean free path (1.78 µm) and effective transport mean free path (1.85 µm). We have used effective transport mean free path to properly describe the scattering strength in anisotropic random media. For improved description of light scattering in beetle scales, we apply complete solutions to the anisotropic diffusion equation, where the solution approach made use of optical boundary layer theory. Our method enables highly accurate determination of mean free paths and extrapolation length in the white beetle scales. [ABSTRACT FROM AUTHOR]

The Zero Field Cooled (ZFC) Exchange Bias (EB) effect in a single phase nanocrystalline Mg-ferrite thin film, deposited on an amorphous quartz substrate using pulsed laser ablation technique, is reported. The film showed a high ZFC EB shift (HE ∼ 190 Oe) at 5 K. The ZFC EB shift decreased with increasing temperature and disappeared at higher temperatures (T > 70 K). This Mg-ferrite thin film also showed the Conventional Exchange Bias (CEB) effect, but unlike many CEB systems, the film showed a decrease in coercivity (HC) under the Field Cooled measurements. The film also showed the training effect in ZFC measurements, which followed the frozen spin relaxation behavior. The observed exchange bias could be attributed to the pinning effect of the surface spins of frozen glassy states at the interface of large ferrimagnetic grains. [ABSTRACT FROM AUTHOR]

In-plane compressively strained α-Sn films have been theoretically predicted and experimentally proven to possess non-trivial electronic states of a 3D topological Dirac semimetal. The robustness of these states typically strongly depends on purity, homogeneity, and stability of the grown material itself. By developing a reliable fabrication process, we were able to grow pure strained α-Sn films on InSb(100), without heating the substrate during growth nor using any dopants. The α-Sn films were grown by molecular beam epitaxy, followed by experimental verification of the achieved chemical purity and structural properties of the film's surface. Local insight into the surface morphology was provided by scanning tunneling microscopy. We detected the existence of compressive strain using Mössbauer spectroscopy, and we observed a remarkable robustness of the grown samples against ambient conditions. The topological character of the samples was confirmed by angle-resolved photoemission spectroscopy, revealing the Dirac cone of the topological surface state. Scanning tunneling spectroscopy, moreover, allowed us to obtain an improved insight into the electronic structure of the 3D topological Dirac semimetal α-Sn above the Fermi level. [ABSTRACT FROM AUTHOR]

Different hybrid structures were obtained by coating magnetic nanoparticles of perovskite type manganite at optimal doping (La0.67Sr0.33MnO3,LSMO) with different quantities of polypyrrole (PPy). The amorphous layer of polypyrrole surrounding the crystalline magnetic core was observed by high resolution transmission electron microscopy (HRTEM) and analyzed by using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) measurements in near edge structure (XANES) techniques. By analyzing the magnetic behavior of the samples one can observe that the surface modification of magnetic nanoparticles by PPy results in an increase in the saturation magnetization of the composites. The process is ascribed to paired electrons transferred from the delocalized π states of the PPy into the outer disordered layers of the manganite. The analysis of pre-edge peak of the Mn K-edge XANES spectra in the case of PPy coated LSMO nanoparticles indicates that the charge transfer between polymer and nanoparticles is (directed) going to missing or distorted oxygen positions, hence increasing the 3d electrons' mobility and orbital hybridization between the neighboring manganese ion. As a consequence, within the surface layers of LSMO nanoparticles, both energy bands disrupted the structure, and the double exchange process between Mn ions was reestablished determining the saturation magnetizations and pre-edge features increase, respectively. [ABSTRACT FROM AUTHOR]

The training effect has been systematically studied in exchange coupled NiFe2O4/NiO nanogranular system. Both exchange bias field (HEB) and vertical magnetization shifts (MShift) can be observed after the system field cooled from 350 K to low temperatures, which decrease monotonically through consecutive loop cycles. During this procedure, linear dependence between HEB and MShift is found for this system, revealing the critical role of the pinned uncompensated spins. With the increase of cooling field, the relative change of HEB becomes more pronounced, which shows that the rapid reduction of the pinned uncompensated spins for high cooling field. Moreover, the reduction of HEB becomes weakened with decreasing measured temperatures, which indicated the spin configuration at low temperatures possesses higher dynamic stability. The cooling field and temperature dependence on training effect is discussed in terms of the evolution of the metastable spin configurations at the interfaces and fitted by a recent theoretical model. [ABSTRACT FROM AUTHOR]

An extensive Monte Carlo (MC) simulation is performed to investigate exchange bias in a novel model of a nanoparticle consisting of a ferromagnetic (FM) core and an amorphous magnetic (AM) shell. The magnetic glassy ordering of the AM shell governed by random magnetic anisotropy (RMA) is shown to be responsible for the unidirectional anisotropy to the FM core. Our MC results show that, while the bias field and coercivity exhibit a strong dependence on RMA strength, which looks like that on the antiferromagnetic (AFM) thickness in traditional FM/AFM bilayers, they are independent of AM thickness. However, the bias field and coercivity abruptly change with increasing small core size and get saturated for a large enough core size. The cooling field and temperature dependencies show the peculiar sign inversion of the bias field. Our study supports the argument that the exchange bias observed in some magnetic nanoparticles or nanocrystallined alloys is not necessarily due to the presence of an AFM phase. [ABSTRACT FROM AUTHOR]

We have studied the coexistence of exchange bias (EB) effect and spin-dependent magnetotransport in a Ni/NiO nanogranular sample by measuring the magnetization (M) and the magnetoresistance (MR) versus the magnetic field (H) in the 5-250 K temperature (T) range, both in zero-field-cooling (ZFC) and field-cooling (FC) conditions. The sample consisted of Ni nanocrystallites (mean size ∼13 nm) dispersed in a NiO matrix; the Ni volume fraction was ∼33%, above the percolation threshold for electrical conductivity, as revealed by the low resistivity (order of 10-3 Ωm) and by its growth with increasing T. The EB and magnetotransport phenomena appear strictly intertwined: the FC M(H) and MR(H) loops exhibit a similar horizontal shift, corresponding to an exchange field of ∼460 Oe at T = 5 K, which decreases with increasing T and disappears at ∼200 K. Both the EB and the magnetotransport properties have been explained, considering the presence of a structurally disordered component of the NiO matrix around the Ni nanocrystallites, whose spin-glass-like magnetic character rules the interface exchange interaction with the Ni phase and the spin-dependent conductivity. [ABSTRACT FROM AUTHOR]

Tunneling magnetoresistance in polycrystalline double perovskite Sr2FeMoO6 exhibits many unusual features, which can be efficiently probed by manipulating the tunnel barriers/grain surfaces. Accordingly, many experimental reports appeared on nanosized particles of Sr2FeMoO6 with largely enhanced grain boundary contributions. However, for the first time we report the existence of a spin-glasslike component, along with conventional ferromagnetism, in well-characterized Sr2FeMoO6 nanoparticles, which has been critically confirmed by the perceptible exchange bias effect, observed in these nanoparticles. Our results suggest that the spin-glass component is likely to reside on the surface of each particle, which probably provides useful clues about the unusual tunneling magnetoresistance responses, always exhibited by nanocrystalline Sr2FeMoO6. [ABSTRACT FROM AUTHOR]

An extended particle agglomeration control model and Monte Carlo simulation methodology were used to describe the behavior of the colloidal aggregation process in presence of inhibitor as a confined fluid. In this work results about the mean cluster size, Z, with respect to different variables, temperature, inhibitor concentration and pore size, are presented and showed that Z strongly depends on the slitlike pore size. In addition, a temperature interval where the heating of the system leads to the particle clustering was found. [ABSTRACT FROM AUTHOR]

We report the low temperature noncollinear magnetic behavior of electron beam evaporated ultrathin Fe/Al multilayer (ML) structures. Investigations have been carried out with ML samples with Fe-layer thicknesses in a range of 10–40 Å and Al-layer thickness of 10 Å. The structural studies show that heavy atomic interdiffusion between Fe and Al layers occurs at the interface, resulting MLs of different complicated structures according to different sublayer thicknesses Brajpuriya, et al.., [Eur. Phys. J. B 51, 131 (2006)]. The magnetic measurements show that these films are “re-entrant” systems and not ordinary ferromagnets as often assumed. The obtained results, interestingly, indicate a transition from ferromagnetic state to a low temperature disordered state where a collective frozen magnetic state with grain moments oriented randomly occurs. We interpret the observed low temperature noncollinear magnetic behavior to be due to random freezing of grain moments. [ABSTRACT FROM AUTHOR]

dc magnetization and ac susceptibility measurements were carried out in a polycrystalline compound with composition Pr0.7Sr0.3CoO3. Low-field dc magnetization and frequency-dependent ac susceptibility results suggest a cluster-glass-like transition at 165 K. When the sample was cooled in a static magnetic field, shifts in the magnetic hysteresis loop were observed at 5 K. Shifts in the hysteresis loop are the typical manifestation of exchange bias (EB) effect. Training effect observed at 5 K is one of the supportive experimental evidences of EB effect which could be satisfactorily analyzed by the relaxation model. EB effect is suggested due to the pinning effect at the ferromagnetic/spin-glass interface in a spontaneously phase separated cluster-glass compound. [ABSTRACT FROM AUTHOR]

The magnetic properties of ∼1.5 nm Co nanoparticles embedded in a diamagnetic Al2O3 or antiferromagnetic (AFM) Cr2O3 matrix were investigated. For Co nanoparticles in Al2O3 matrix, a typical behavior of weakly interacting nanoparticles is observed, characterized by a superparamagnetic regime and a progressive blocking of particle moments centered at B>14 K. On the other hand, when the Co nanoparticles are immersed in a Cr2O3 matrix a very different magnetic behavior was found. The system shows large irreversibility in field-cooling/zero-field-cooling magnetization curves and much larger coercivity was observed even up to room temperature. Hysteresis loop shift is present when the system is field-cooled from a temperature above the Cr2O3 Néel temperature. We found that the exchange bias field follows a Brillouin type temperature dependence and goes to zero at TN. These results evidence the enhancement of thermal stability of the Co nanoparticle moments, associated to the increase of anisotropy due to the interface exchange interaction between the ferromagnetic particles and the AFM Cr2O3 matrix. [ABSTRACT FROM AUTHOR]

Partially oxidized fcc FePd and FePt nanoparticles with mean diameters of 5 and 3 nm, respectively, were synthesized by a reverse micelle polyol process. In situ measurements of magnetic and structural properties during annealing showed a large increase in the magnetocrystalline anisotropy and in the Curie temperature of the nanoparticles due to (i) a phase transition from A1 to L10 and (ii) a simultaneous phase separation between a metallic core and an iron oxide shell. These occurred at 675 K in the FePd nanoparticles and at above 850 K for the FePt. The Curie temperature of the nanoparticles was found to be about 850 K, an increase of more than 100 K from the bulk L10 phase. The ferromagnetic resonance results are discussed and compared with a phenomenological model that makes it possible to estimate the magnetocrystalline anisotropy as 1.6×105 and 1.5×106 J m-3 in FePd and FePt, respectively. Exchange coupling between the core and the shell explains both the high magnetocrystalline anisotropy of the core and the high Curie temperature of the shell. [ABSTRACT FROM AUTHOR]

In this study we address the role of surface anisotropy on the hysteretic properties of magnetite Fe3O4 nanoparticles and the circumstances yielding both horizontal and vertical shifts in the hysteresis loops. Our analysis involves temperature dependence and particle size effects. Different particle sizes ranging from 2 up to 7 nm were considered. Our theoretical framework is based on a three-dimensional classical Heisenberg model with nearest magnetic neighbor interactions involving tetrahedral (A) and octahedral (B) irons. Cubic magnetocrystalline anisotropy for core spins, single-ion site anisotropy for surface spins, and interaction with a uniform external magnetic field were considered. Our results revealed the onset of low temperature exchange bias field, which can be positive or negative at high enough values of the surface anisotropy constant (KS). Susceptibility data, computed separately for the core and the surface, suggest differences in the hard-soft magnetic character at the core-surface interface. Such differences are KS-driven and depend on the system size. Such a hard-soft interplay, via the surface anisotropy, is the proposed mechanism for explaining the observed exchange bias phenomenology. Our results indicate also that the strongly pinned spins at high enough surface anisotropy values are responsible for both the horizontal and vertical shifts in the hysteresis loops. The dependences of the switching and exchange bias fields with the surface anisotropy and temperature are finally discussed. [ABSTRACT FROM AUTHOR]

We investigate the exchange bias phenomenon in the layered cobaltite Sr1.5Pr0.5CoO4 by using magnetometry. The exchange bias is strongly dependent on the cooling magnetic field as well as the measuring field. These results suggest that the exchange coupling at the interfaces between the ferromagnetic (FM) regions and the spin-glass (SG) regions may induce an exchange anisotropy. The observed exchange bias effect is suggested to originate from the pinning to FM moments by frozen spins in the SG regions along the cooling field direction. Our results also expand the concept of the magnetically tunable exchange bias, which can contribute to the potential applications for spintronic devices. [ABSTRACT FROM AUTHOR]

The structure, phase components, and magnetic properties of antiferromagnetic coupled Fe2O3 and NiO nanocomposites have been investigated. A negative exchange bias field of about 2 kOe and the anomalous shape of hysteresis loop are observed, which may be related to uncompensated and pinned antiferromagnetic spins at the interface between ferrimagnetic and antiferromagnetic phases in the powders. Furthermore, the exchange bias field varies with the strength of cooling field, and the exchange bias field HE of 0.76 kOe is observed in antiferromagnetic-antiferromagnetic system. [ABSTRACT FROM AUTHOR]