Magnetization studies in amorphous Co80-x Gdx B20

We have studied amorphous Co80-x Gdx B20 alloys prepared by melt spinning technique. The Gd moment at 4.2 K is found to be 7 µB which agrees with the theoretical value indicating a collinear spin structure. The magnetic compensation at 4.2 K occurs for x close to 10.3. The mean-field theory has been used to explain the temperature dependence of the magnetization. The exchange interactions between Co-Co and Co-Gd atom pairs have also been evaluated.We have studied amorphous Co80-x Gdx B20 alloys prepared by melt spinning technique. The Gd moment at 4.2 K is found to be 7 µB which agrees with the theoretical value indicating a collinear spin structure. The magnetic compensation at 4.2 K occurs for x close to 10.3. The mean-field theory has been used to explain the temperature dependence of the magnetization. The exchange interactions between Co-Co and Co-Gd atom pairs have also been evaluated

Design of a Low-cost and Compact Radiometer for Spectral Acquisition of Vegetation and Bare Soil

We describe, in this article, the design of a low-cost and compact radiometer with five analog channels for spectral acquisition: four in the visible (blue, green, red and panchromatic) and one channel in the near-infrared. This small embedded system is based on an 8-bit microcontroller for automatic data acquisition, calibrating, storing and serial link processing with a compatible PC, through a C++ application software provided to handle and deal with the mass of data collected and stored in an EEPROM. The acquisition of spectral reflectance measurements of an object for different wavelengths allows the construction of a characteristic curve, named spectral signature of the object. The study of the spectral signatures of different types of surfaces such as water, bare ground or vegetation allows their identification in remote sensing image processing, and consequently, facilitates the interpretation of this kind of data, as, for instance, the AVHRR data of the HRPT images acquired and freely distributed by the satellite NOAA

Magnetic properties in amorphous Co95­xDyxZr5 thin films

Amorphous Co95-xDyxZr5 thin films were prepared by RF sputtering and their magnetic properties were studied as a function of temperature and for the composition range 0<x<30. The mean field theory has been used to explain the temperature dependence of the magnetization. The exchange interactions between Co-Co and Dy-Co atom pairs have been evaluated. The magnetic phase diagrams are presented.Amorphous Co95-xDyxZr5 thin films were prepared by RF sputtering and their magnetic properties were studied as a function of temperature and for the composition range 0<x<30. The mean field theory has been used to explain the temperature dependence of the magnetization. The exchange interactions between Co-Co and Dy-Co atom pairs have been evaluated. The magnetic phase diagrams are presented

Ab initio study of magnetism at the TiO2/LaAlO3 interface

In this paper we study the possible relation between the electronic and magnetic structure of the TiO2/LaAlO3 interface and the unexpected magnetism found in undoped TiO2 films grown on LaAlO$_3$. We concentrate on the role played by structural relaxation and interfacial oxygen vacancies. LaAlO3 has a layered structure along the (001) direction with alternating LaO and AlO2 planes, with nominal charges of +1 and -1, respectively. As a consequence of that, an oxygen deficient TiO2 film with anatase structure will grow preferently on the AlO2 surface layer. We have therefore performed ab-initio calculations for superlattices with TiO2/AlO2 interfaces with interfacial oxygen vacancies. Our main results are that vacancies lead to a change in the valence state of neighbour Ti atoms but not necessarily to a magnetic solution and that the appearance of magnetism depends also on structural details, such as second neighbor positions. These results are obtained using both the LSDA and LSDA+U approximations.Comment: Accepted for publication in Journal of Materials Scienc

Correlations of structural, magnetic, and dielectric properties of undoped and doped CaCu3Ti4O12

The present work reports synthesis, as well as a detailed and careful characterization of structural, magnetic, and dielectric properties of differently tempered undoped and doped CaCu3Ti4O12 (CCTO) ceramics. For this purpose, neutron and x-ray powder diffraction, SQUID measurements, and dielectric spectroscopy have been performed. Mn-, Fe-, and Ni-doped CCTO ceramics were investigated in great detail to document the influence of low-level doping with 3d metals on the antiferromagnetic structure and dielectric properties. In the light of possible magnetoelectric coupling in these doped ceramics, the dielectric measurements were also carried out in external magnetic fields up to 7 T, showing a minor but significant dependence of the dielectric constant on the applied magnetic field. Undoped CCTO is well-known for its colossal dielectric constant in a broad frequency and temperature range. With the present extended characterization of doped as well as undoped CCTO, we want to address the question why doping with only 1% Mn or 0.5% Fe decreases the room-temperature dielectric constant of CCTO by a factor of ~100 with a concomitant reduction of the conductivity, whereas 0.5% Ni doping changes the dielectric properties only slightly. In addition, diffraction experiments and magnetic investigations were undertaken to check for possible correlations of the magnitude of the colossal dielectric constants with structural details or with magnetic properties like the magnetic ordering, the Curie-Weiss temperatures, or the paramagnetic moment. It is revealed, that while the magnetic ordering temperature and the effective moment of all investigated CCTO ceramics are rather similar, there is a dramatic influence of doping and tempering time on the Curie-Weiss constant.Comment: 10 pages, 11 figure

Monitoring and identification of marine oil spills using advanced synthetic aperture radar images

The aim of this study is to propose and test a new methodology for detection of oil spills in the world oceans from advanced synthetic aperture radar imagery embedded in ENVISAT satellite (ENVISAT-ASAR). The proposed and applied methodology includes four levels: data acquisition, dark spots detection, features extraction and dark spots classification for discrimination between oil spills and look-alikes. Level 1 contains the ENVISAT-ASAR wide swath mode data acquisition. Level 2 begins with a visual interpretation based on experience and a priori information concerning location, external information about weather conditions, differences in shape, and contrast to surroundings between oil spills and look-alikes, then filtering and segmentation. Level 3 contains extraction of features from the detected dark spots. Level 4 aim is to discriminate oil spills from look-alikes using the features extracted by means of object-based fuzzy classification. As a result, oil slicks are discriminated from look-alikes with an overall accuracy classification of 91% for oil slicks and 86% for look-alikes. Finally, to validate our results, the method has been tested by comparing the areas of the automatically detected oil spills (object-based fuzzy classification) with the areas of the manually detected oil spills (region of interest), by means of area ratios

Elaboration and characterization of clay-sand composite based on Juncus acutus fibers

International audienceThe study reported in this paper was undertaken to investigate the feasibility of lightweight construction materials, based on vegetable fibres. This innovative material consisted of mixture of natural clay (60%) and natural sand (40%) reinforced with different levels of fibers extracted from Jancus acutus ``Smar''. The fibers were used as partial replacement of sand in mixture by volume at: 0% (Control Specimen), 5%, 10%, and 20%. The objective of this work is to evaluate the physico-mechanical properties, through the examination of materials lightning, mechanical strengths (compressive and flexural). Due to the high hygroscopic nature of the vegetable fibers, the thermal conductivity of the composite materials was measured at both wet and dry state at different volumes of Juncus fibers replacement. Test-results have shown that the addition of 20% fibers decreased the composite bulk density from 1900 kg/m(3) to 1100 kg/m(3), which results in a high reduction of mechanical performances in terms of compressive and flexural strengths. The experimental investigation of thermal behaviour of this composite has shown that the increase of fibers volume leads to a significant decrease in thermal conductivity. For a composite containing 20% of fibers replacement, the dry thermal conductivity decreased from 0.902 W/m.K for control specimen (without fibers) to a value of 0.327 W/m.K. However, at wet state, the corresponding thermal conductivity decreased from 1.543 W/m.K to 0.361 W/m.K. Despite the decrease in mechanical strengths, the resulting composite can thus be considered as a promising candidate for use in thermal insulation material, because a conductivity of 0.350 W/m.K is generally considered as the worst acceptable value for insulating building material. (C) 2019 Elsevier Ltd. All rights reserved