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Register a new userMagnetic properties of bismuth-cobalt oxides doped by erbium
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We synthesized bismuth - cobalt oxide doped by erbium with general formula Bi3-xErxCoO3-y. Compound has structure of delta-form bismuth oxide. Magnetic properties of the compound were measured by Faradays method using quartz scales in the temperature range of 80-500 K. The magnetic susceptibility and effective magnetic moment were calculated.
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We synthesized pure and Co-doped (6.25 12.5 at.) ZrO$_2$ nanopowders in order to study their magnetic properties.We analyzed magnetic behavior as a function of the amount of Co and the oxygenation, which was controlled by low pressure thermal treatments. As prepared pure and Co-doped samples are diamagnetic and paramagnetic respectively. Ferromagnetism can be induced by performing low pressure thermal treatments, which becomes stronger as the dwell time of the thermal treatment is increased. This behavior can be reversed, recovering the initial diamagnetic or paramagnetic behavior, by performing reoxidizing thermal treatments. Also, a cumulative increase can be observed in the saturation of the magnetization with the number of low pressure thermal treatments performed. We believe that this phenomenon indicates that cobalt segregation induced by the thermal treatments is the responsible for the magnetic properties of the ZrO$_2$ Co system.
Single phase nickel-cobalt-titanate thin films with a formula A1+2xTi1-xO3, where A is Ni2+,Co2+ and -0.25<x<1, were grown by pulsed laser deposition on sapphire substrates. There is a large window in which both Ni/Co ratio and x can be chosen independently. In the prototype ilmenite and corundum structures one third of the octahedra are vacant. The reported structure is obtained by filling vacant (x>0) or emptying filled (x<0) octahedra. When x = 1 all octahedra are filled. Two factors controlling the magnetism and crystal distortion are identified. First is a direct overlap between the adjacent cation d-orbitals resulting in a bond formation and magnetic interactions between the cations. This is most clearly revealed as a crystal distortion in the x approximately 0 compositions with approximately equal amounts of Ni and Co: the distortion of the x approximately 0 compound is a function of Ni/Co ratio. The second factor is x, which controls the cation shift towards a vacant octahedron. The displacement decreases and the symmetry increases with decreasing Ti content as was revealed by x-ray diffraction and Raman spectroscopy. When all octahedra are filled the cations prefer octahedron center positions. Also the number density of cations has increased by a factor of 50 percent when compared to the ilmenite structure. The number density ratios of Ni/Co cations between x=1 and x=0 compounds is 3. The Raman and x-ray diffraction data collected on samples with x = 1 or close to 1 are interpreted in terms of P63/mmc space group.
Multiferroic bismuth ferrite (BiFeO3) nanopowders have been obtained in room temperature by mechanical synthesis. Depending on the post-synthesis processing the nanopowders have exhibited differences in the mean sizes, presence of amorphous layer and/or secondary phases. Extended magnetic study performed for fresh, annealed and hot-pressed nanopowders have revealed substantial improvement of the magnetic properties in the as-prepared powder.
Based on first-principles calculations, we predict that the magnetic anisotropy energy (MAE) of Co-doped TiO$_2$ sensitively depends on carrier accumulation. This magnetoelectric phenomenon provides a promising route to directly manipulate the magnetization direction of diluted magnetic semiconductor by external electric-fields. We calculate the band structures and reveal the origin of carrier-dependent MAE in k-space. In fact, the carrier accumulation shifts the Fermi energy and regulates the competing contributions to MAE. The first-principles calculations provide a straightforward way to design spintronics materials with electrically controllable spin direction.
Rare-earth-doped optical materials are important for light sources in optoelectronics, as well as for efficient optical amplification elements and other elements of photonics. On the basis of the previously developed method of anhydrous, low-temperature synthesis of Er/Yb oxides from their chlorides we fabricated proper nanoparticles with defined parameters and used them for the development of optically transparent, luminescent polymer nanocomposite with low optical scattering, suitable for direct, light-induced formation of photonic elements. Introduction of preformed gold nanoparticles in such a nanocomposite was also performed and an enhancement of luminescence due to the influence of plasmon effects was detected.
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