Studies of structural, magnetic and dielectric properties of X-type Barium Zinc hexaferrite Ba2Zn2Fe28O46 powder prepared by combustion treatment method using ginger root extract as a green reducing agent

Various quantities of ginger (Zingiber officinale) root extract were used to prepare X-type Barium–Zinc hexaferrite with the chemical composition Ba2Zn2Fe28O46. The powders were prepared using a combustion treatment method, being pre-heated at 550 °C for 4 h with the ginger as a fuel, followed by final heating to 900 °C for 5 h and natural cooling to room temperature to obtain Ba2Zn2Fe28O46 hexagonal ferrite powder. The phase composition of heated powder samples was investigated by X-ray diffraction (XRD), indicating the formation of a mixture of X-type and hematite (α-Fe2O3). Up to 82.6%, X-ferrite was formed at 900 °C with 52.5 g of ginger root extract. Dielectric analysis of the prepared samples shows the frequency-dependent phenomena. All samples were hard magnets, with coercivity values (HC) between 262.2 and 318.3 kA m−1, and squareness ratios > 0.5. The sample prepared with 52.5 g ginger root extract possesses the highest value of saturation magnetisation (MS = 33.87 Am2 kg−1) in comparison with the other prepared samples. Therefore, ginger was shown to be a useful natural plant extract as a reducing fuel for the low-temperature synthesis of X-ferrites. The sample prepared with 35 g ginger root extract shows a broad loss tangent resonance peak between 10 kHz and 100 kHz, while other samples show loss tangent resonance peaks between 300 kHz and 2 MHz frequency range

A study of the gravitational wave form from pulsars II

We present analytical and numerical studies of the Fourier transform (FT) of the gravitational wave (GW) signal from a pulsar, taking into account the rotation and orbital motion of the Earth. We also briefly discuss the Zak-Gelfand Integral Transform. The Zak-Gelfand Integral Transform that arises in our analytic approach has also been useful for Schrodinger operators in periodic potentials in condensed matter physics (Bloch wave functions).Comment: 6 pages, Sparkler talk given at the Amaldi Conference on Gravitational waves, July 10th, 2001. Submitted to Classical and Quantum Gravit

On gravitational waves emitted by an ensemble of rotating neutron stars

We study the possibility to detect the gravitational wave background generated by all the neutron stars in the Galaxy with only one gravitational wave interferometric detector. The proposed strategy consists in squaring the detector's output and searching for a sidereal modulation. The shape of the squared signal is computed for a disk and a halo distribution of neutron stars. The required noise stability of the interferometric detector is discussed. We argue that a possible population of old neutron stars, originating from a high stellar formation rate at the birth of the Galaxy and not emitting as radio pulsars, could be detected by the proposed technique in the low frequency range of interferometric experiments.Comment: 14 pages, 2 PostScript figures, RevTeX, accepted for publication in Physical Review

The effect of heat treatment on the microstructure and mechanical properties of 2d nanostructured au/nife system

Nanostructured NiFe film was obtained on silicon with a thin gold sublayer via pulsed electrodeposition and annealed at a temperature from 100 to 400◦C in order to study the effect of heat treatment on the surface microstructure and mechanical properties. High-resolution atomic force microscopy made it possible to trace stepwise evolving microstructure under the influence of heat treatment. It was found that NiFe film grains undergo coalescence twice—at ~100 and ~300°C—in the process of a gradual increase in grain size. The mechanical properties of the Au/NiFe nanostructured system have been investigated by nanoindentation at two various indentation depths, 10 and 50 nm. The results showed the opposite effect of heat treatment on the mechanical properties in the near-surface layer and in the material volume. Surface homogenization in combination with oxidation activation leads to abnormal strengthening and hardening-up of the near-surface layer. At the same time, a nonlinear decrease in hardness and Young’s modulus with increasing temperature of heat treatment characterizes the internal volume of nanostructured NiFe. An explanation of this phenomenon was found in the complex effect of changing the ratio of grain volume/grain boundaries and increasing the concentration of thermally activated diffuse gold atoms from the sublayer to the NiFe film. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.Funding: The work was supported by Act 211 Government of the Russian Federation, contract № 02.A03.21.0011

An investigation of uniform expansions of large order Bessel functions in Gravitational Wave Signals from Pulsars

In this work, we extend the analytic treatment of Bessel functions of large order and/or argument. We examine uniform asymptotic Bessel function expansions and show their accuracy and range of validity. Such situations arise in a variety of applications, in particular the Fourier transform of the gravitational wave signal from a pulsar. The uniform expansion we consider here is found to be valid in the entire range of the argument

Inhomogeneous Bulk Viscous Fluid Universe with Electromagnetic Field and Variable Λ\Lambda-Term

Cylindrically symmetric inhomogeneous cosmological model for bulk viscous fluid distribution with electromagnetic field is obtained. The source of the magnetic field is due to an electric current produced along the z-axis. $F_{12}$ is the non-vanishing component of electromagnetic field tensor. To get the deterministic solution, it has been assumed that the expansion $\theta$ in the model is proportional to the shear $\sigma$. The values of cosmological constant for these models are found to be small and positive at late time, which are consistent with the results from recent supernovae Ia observations. Physical and geometric aspects of the models are also discussed in presence and absence of magnetic field.Comment: 21 pages, 8 figure

Signal analysis of the gravitational waveform of pulsars

We present signal analysis for the detection of gravitational radiation from pulsars. Typically the observation times will be of the order of a few weeks or months. Due to the rotation and orbital motion of the Earth, a monochromatic signal gets frequency and amplitude modulated. The effect of both these modulations is to smear out the monochromatic signal into a small bandwidth about the signal frequency of the wave. However, the effect on the Fourier transform of frequency modulation is much more severe compared to amplitude modulation in that the height of the peak is reduced drastically. The spread in the frequency, Δf ≈ 2πf0R/c , where f0 is the frequency of the signal, R the radius of the Earth and c the velocity of light. Further, we develop analytical approximations to Fourier transform of the pulsar taking into account the rotation of the Earth and then the orbital correction to the signal. lnspection of the expression shows that for a 1kHz signal and one day observation time, the signal is spread into about 100 bands. These calculations are performed for arbitrary orientations of the detector and the arbitrary wave parameters

Structural, magnetic, magnetocaloric and critical exponents of oxide manganite La0.7Sr0.3Mn0.95Fe0.05O3

International audienc

Structural, magnetic, magnetocaloric and critical behaviour of La0.67Ba0.22Sr0.11Mn0.95Ti0.05O3 nanopowder

International audienc

Elucidation of microwave absorption mechanisms in Co–Ga substituted Ba–Sr hexaferrites in X-band

The tunable microwave absorbers are used to combat the electromagnetic pollution created by the development of high speed electronic devices. In the present paper, we report microwave absorption characteristics of M-type Ba0.5Sr0.5CoxGaxFe12−2xO19 (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) hexagonal ferrite compositions prepared by using double sintering ceramic method. X-ray diffraction analysis of the prepared compositions revealed the formation of M-phase along with the minor traces of hematite in substituted compositions. The microwave absorption has been elucidated substantially through various mechanisms in the test frequency range from 8.2 to 12.4 GHz, which is still partially explored in literature. The substitution of Co2+ and Ga3+ ions enhances microwave absorption, bandwidth, decreases thickness and improves impedance matching. The hysteresis parameters also comply with the microwave absorption. The optimal reflection loss of − 29.74 dB is observed in the composition x = 0.2 at 8.28 GHz with 2.0 mm thickness. The investigated mechanisms of microwave absorption can be incorporated to optimize the absorption and design of the microwave absorbers