Search results for " OPT"
showing 10 items of 13620 documents
Tetragonal Heusler Compounds for Spintronics
2013
With respect to the requirements of spin torque transfer (STT) materials, one the most promising materials families are the tunable tetragonal Heusler compounds based on Mn2YZ (Y=Co,Fe,Ni,Rh,...; Z=Al, Ga, Sn). They form the inverse cubic Heusler structure with three distinct magnetic sublattices, which allows a fine tuning of the magnetic properties. Starting with the stoichiometric Mn3Ga compound, we explored the complete phase diagram of Mn3-xYxZ (Y=Co, Fe, Ni and Z=Ga ). All series exhibit thermally stable magnetic properties. As we demonstrate, Mn3-xFexGa series, which are tetragonal over the whole range of compositions, are good as hard magnets, whereas magnetically more weak Mn3-xNix…
Space Charge Measurement under DC and DC Periodic Waveform
2018
In High Voltage systems, Partial Discharges (PDs) monitoring are one of the main diagnostic instrument to evaluate the reliability of the apparatus. Under Alternating Current (AC) stress, PDs detection and recognition techniques are well consolidated. On the contrary, the monitoring of PDs under Direct Current (DC) stress is difficult due to complexities related to the nature of the phenomenon, which cause the beginning of PDs events in proximity of the dielectric breakdown. This problem has been partially overcome by using a continuous Periodic waveform (DCP) with positive average value, as described in a recent published work. Under DC stress, another degradation factor is the Space Charg…
The effects of the additive of Eu ions on elastic and electric properties of BaTiO3ceramics
2016
ABSTRACTThe BaTiO3 and BaTiO3+X%wt.Eu2O3 (X = 1, 2, 3) ceramics were prepared by a solid phase reaction. The structural and morphology studies were carried out by means of an X-ray diffraction technique and scanning electron microscopy, respectively. Elastic moduli were determined with the use of an ultrasonic method. The dielectric permittivity (ϵ′) and tanδ as a function of composition and temperature were investigated. The increasing concentration of Eu ions leads to a slight shift of the Curie temperature and changes the characteristics of ϵ′ and tanδ. The structural, mechanical and dielectric properties of the BTEX ceramics were discussed in terms of microstructure and dopants contents.
SrTiO3-doping effect on dielectric and ferroelectric behavior of Na0.5Bi0.5 TiO3 ceramics
2018
Lead-free (Na0.5Bi0.5)1-xSrxTiO3 ceramics (x = 0–0.04) were synthesized by a conventional mixed-oxide technique. The microstructure study showed a dense structure, in good agreement with that of ab...
Preparation and dielectric properties of (Na 0.5 K 0.5 )NbO 3 ceramics with ZnO and CdO addition
2019
The sintering conditions, phase structure, and electrical properties of the ZnO and CdO doped (Na0.5K0.5)NbO3 (NKN) ceramics were investigated and discussed. All the samples were prepared by a solid state reaction method. The addition of 1 wt% CdO and ZnO as a sintering aid increases the density and lowering the sintering temperature. XRD analysis indicated perovskite structure with monoclinic symmetry. The investigated samples are good quality, the grains are well shaped without a glassy phase. The results of dielectric measurements revealed, that the dielectric properties of NKN based ceramics are stable in the wide temperature range.
OPTIMIZATION OF A NOVEL MAGNETO-RHEOLOGICAL DEVICE WITH PERMANENT MAGNETS
2017
In this paper a novel evolutionary algorithm is used for the optimization of the performance of a magnetorheological (MR) device, capable to transmit torque between two shafts and powered by a system of Permanent Magnets (PMs). The stochastic, evolutionary, global optimization algorithm is based on a modified version of the self-organizing map. It uses a dedicated simplified analytical model of the device, developed in order to obtain a fast and accurate evaluation of the torque. Then, by means this model, the cost function to find the optimal parameters of the device is defined. Once the optimal parameters are identified, the performance of the proposed device is simulated by means of a FE…
How activator ion concentration affects spectroscopic properties on Ba4Y3F17: Er3+, Yb3+, a new perspective up-conversion material
2018
Abstract Ba4Y3F17 with Er3+ and Yb3+, a promising material for up-conversion luminescence, was synthesized. Excellent isomorphic capacity was detected. Low-temperature measurements show that erbium ions are incorporated in multiple lattice positions, which is inconsistent with the current model of Ba4Y3F17 crystal lattice structure. Activator ion concentration has a different impact on 4S3/2 and 4F9/2, states (for the green and red luminescence, respectively) depopulation. Energy transfer from Er3+ 4S3/2 state to Yb3+ is observed even at low temperature (15 K) while Er-Er cross-relaxation is observed from 120 K and above. Yb3+ concentration has a great impact to red-to-green up-conversion l…
Tuning the electronic and magnetic properties of 2D g-GaN by H adsorption: An ab-initio study
2019
Abstract We have theoretically studied the structural, electronic and magnetic properties of the hydrogen adsorption on a honeycomb gallium-nitride two-dimensional monolayer (2D g-GaN). Results indicate that the band gap energy can be systematically tuned by the hydrogen coverage on the 2D g-GaN in the diluted limit. In addition, a total magnetic moment can be induced in the 2D g-GaN by hydrogen adsorption due to s-p interaction and band structure effects. Although hydrogen adsorption on top of nitrogen atoms shows the most stable energy in the 2D g-GaN, the most stable ferromagnetism -with a nonzero magnetic moment-is obtained when hydrogen is adsorbed on top of Ga atoms. These results ind…
Zn-substituted iron oxide nanoparticles from thermal decomposition and their thermally treated derivatives for magnetic solid-phase extraction
2020
Abstract Controlled thermal decomposition of zinc and iron acetylacetonates in the presence of oleic acid and oleylamine provided surfactant-capped magnetic nanoparticles with narrow size distribution and the mean diameter of ≈15 nm. The combined study by XRD, XRF and Mossbauer spectroscopy revealed three important features of the as-prepared nanoparticles. First, the actual ratio of Zn:Fe was considerably lower in the product compared to the initial ratio of metal precursors (0.14 vs. 0.50). Second, a pure stoichiometric Zn-doped magnetite system, specifically of the composition Zn0.37Fe2.63O4, with no signatures of oxidation to maghemite was formed. Third, Zn2+ ions were distributed at bo…
Mechanical properties of macroscopic magnetocrystals
2019
Abstract We studied experimentally and by numerical simulations the mechanical response of arrays of macroscopic magnetic spheres when an external stress is applied. First, the tensile strength of single chains and ribbons was analyzed. Then, simple cubic (cP), hexagonal (Hx) and hybrid (cP-Hx) structures, called here magnetocrystals , were assembled and subjected to tensile stress, bending stress and torsion until failure was reached. Atomistic crystalline structures are isotropic, but in the case of magnetocrystals, even when geometric isotropy is obeyed, dipolar magnetic interactions introduce a physical anisotropy which modifies, in a non-usual manner, the structures response to the kin…