Thermomagnetic history effects across the first order magneto-structural transition in the giant magnetocaloric Fe-Rh alloy

We investigate the electronic structure of Sr₂FeMoO₆/SrTiO₃ (SFMO/STO) multilayers using the ab initio Full Potential Linearized Augmented Plane Wave method in order to study their properties within the GGA and GGA+U methods. We examin more especially the role of the interface on the magnetic and transport properties of these multilayers taking into account a possible Fe deficiency at the interface and we show that bulk behaviour is rapidly recovered due to the strong localization of the interfacial perturbation. For perfect interfaces, the whole structure is found half-metallic within the GGA+U method; the situation being ambiguous within the GGA method where SFMO is at the limit of being half-metallic depending on the structural deformation induced by the STO layer. This leads us to the conclusion that such a system could be used as injection electrode and tunnel barrier in magnetic tunnel junctions with a fully spin polarized injected current. For Fe deficient interfaces, we show that the interfacial densities of states are nearly unpolarized showing that this kind of imperfection has potentially a strong impact on the properties of the multilayers.     

Anharmonic effects on lattice resonant modes of impure metallic crystals

The effect of lattice anharmonicity on the resonant modes of dilute impurities for Au-Cu, Au-Ag and W-Cr metallic systems are studied from the poles of the double time temperature dependent impure Green’s function of these crystals. The third order force constants used in the present work are derived assuming the systems to obey the Lennard-Jones potential. The inclusion of lattice anharmonicity has been found to increase the resonant frequency which depends upon the mass defect, force constant change parameter and the impurity concentration terms. Some interesting features about the phase shift and the change in width of the vibrational spectrum are reported at room temperature for the isotopic defects and the defects interacting with host atoms. The results are found to be in qualitative agreement with the experiments on the systems considered.     

An acoustic backscattering technique for the detection of transient cavitation produced by microsecond pulses of ultrasound

An acoustic backscattering technique for detecting transient cavitation produced by 10-microseconds-long pulses of 757-kHz ultrasound is described. The system employs 10-microseconds-long, 30-MHz center frequency tone bursts that scatter from cavitation microbubbles. Experiments were performed with suspensions of hydrophobic polystyrene spheres in ultraclean water. Transient cavitation threshold pressures measured with the active cavitation detector (ACD) were always less than or equal to those measured using a passive acoustic detection scheme. The measured cavitation thresholds decreased with increasing dissolved gas content and increasing suspended particle concentration. Results also show that ultrasonic irradiation of the polystyrene sphere suspensions by the ACD lowered the threshold pressure measured with the passive detector. A possible mechanism through which suspensions of hydrophobic particles might nucleate bubbles is presented.     

Designing copper–zirconium based nanowires for improving yield strength and plasticity by configuring surface atoms

Epitaxial-Bain-Path and Uniaxial-Bain-Path studies reveal that a B2-CuZr nanowire with Zr atoms on the surface is energetically more stable compared to a B2-CuZr nanowire with Cu atoms on the surface. Nanowires of cross-sectional dimensions in the range of ~20–50 Å are considered. Such stability is also correlated with the initial state of stress in the nanowires. It is also demonstrated here that a more stable structure, i.e., B2-CuZr nanowire with Zr atoms at surface shows improved yield strength compared to B2-CuZr nanowire with Cu atoms at surface site, over range of temperature under both the tensile and the compressive loadings. Nearly 18% increase in the average yield strength under tensile loading and nearly 26% increase in the averaged yield strength under compressive loading are observed for nanowires with various cross-sectional dimensions and temperatures. It is also observed that the B2-CuZr nanowire with Cu atom at the surface site shows a decrease in failure/plastic strain with an increase in temperature. On the other hand, B2-CuZr nanowires with Zr at the surface site shows an improvement in failure/plastic strain, specially at higher temperature as compared to the B2-CuZr nanowires which are having Cu atoms at the surface site. Finally, a possible design methodology for an energetically stable nano-structure with improved thermo-mechanical properties via manipulating the surface atom configuration is proposed.     

TEM characterization of chemically synthesized copper–gold nanoparticles

Dodecanethiol-capped Cu–Au nanoparticles, synthesized via a successive two-phase (water/toluene) and galvanic-exchange procedure, were characterized using transmission electron microscopy (TEM). The size range of the particles is around 1–7 nm. Electron-induced morphological evolution was observed under high resolution (HR) TEM. Cuboctahedral morphology was found to be thermodynamically stable. Electron-induced aggregation of two particles was also observed. Chemical ordering of cuboctahedral particles was studied by atomic-resolution high angle annular dark field (HAADF) imaging in scanning TEM (STEM) mode and energy dispersive X-ray (EDX) element mapping using a silicon drift detector (SDD). The particles were found to be Cu–Au mixed, and to be stable in air. Surface plasmon resonance (SPR), which is dependent on local structure and morphology, was investigated by electron energy loss spectroscopy (EELS).     

Wavelength-scanning Talbot effect and its application for arbitrary three-dimensional step-height measurement

We demonstrate the phenomenon of Talbot self-image plane shift by tuning the wavelength of the broadband light source. A superluminescent diode (SLD) is used as a broad-band light source and an acousto-optic tunable filter (AOTF) as wavelength-scanning device. A periodic grating is illuminated by the wavelength tuned light of SLD using AOTF and Talbot self-image plane is shifted continuously in the longitudinal direction without mechanically moving the grating. The wavelength-scanning Talbot effect is then implemented for the measurement of arbitrary step-height of discontinuous objects with extended range. The main advantages of the proposed system are non-mechanical scanning, high stability because of it’s common-path geometry and compactness. Since the measurement of the phase is not required the system is free from phase ambiguity problem and therefore, the range of measurement is large as compare to interferometric techniques.     

Synthesis, structural and electrical properties of La and Nb modified Bi4Ti3O12 ferroelectric ceramics

Polycrystalline ceramic samples of Bi_4−xLa_xTi₃O₁₂ (x=0.0, 0.5 and 1) and Bi_3.5La_0.5Ti_3−yNb_yO₁₂ (y=0.02 and 0.04) have been synthesized by standard high temperature solid state reaction method using high purity oxides and carbonates. The effect of lanthanum doping on Bi-site and Nb doping on Ti-site on the structural and electrical properties of Bi₄Ti₃O₁₂ powders was investigated by X-ray diffraction, scanning electron microscopy, dc conductivity and dielectric studies. A better agreement between the observed and calculated X-ray diffraction pattern was obtained by performing the Rietveld refinement with a structural model using the non-centrosymmetric space group Fmmm in all the cases. A better agreement between observed and calculated d-values also shows that the lattice parameters calculated using the Rietveld refinement analysis are better. The increase in lanthanum and niobium contents does not lead to any secondary phases. It is found that La³⁺ doping reduces the material grain size and changes its morphology from the plate-like form to a spherical staking like form. The substitution of Nb for Ti ions affected the degree of disorder and modified the dielectric properties leading to more resistive ceramic compounds. The shape and size of the grains are strongly influenced by the addition of niobium to the system. The activation energies of all the compounds were calculated by measuring their dc electrical conductivities. The frequency and temperature dependent dielectric behavior of all the compounds have also been studied and the results are discussed in detail. The substitution of La and Nb on the Bi and Ti sites decreased the T_c and improved the dielectric and ferroelectric behavior.     

Semiconductor optical amplifier (SOA)-assisted Sagnac switch for designing of all-optical tri-state logic gates

Tri-state logic plays a significant role in carry free arithmetical operation. Design of all-optical scheme of three basic tri-state logical operation (NOT, AND, OR) with the help of polarization encoded semiconductor optical amplifier (SOA)-assisted Sagnac interferometric switch has been studied and investigated in this present paper. Numerical simulation is also presented, which verifies the theoretical results. Insertion loss, contrast ratio, extinction ratio, amplitude modulation, bit error rate and signal to noise ratio values have also been analyzed.