Synthesis, structure and magnetic properties of Y3Fe5-xAlxO12 garnets prepared by the soft chemical method

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Comparative study on structure and magnetic properties of polycrystalline PrxY1-xBa2Cu3O7-delta prepared in oxygen and argon atmosphere

We report a systematic study on the influence of the synthesis routes on the structural and magnetic properties of polycrystalline PrxY1-xBa2Cu3O7-delta. We have prepared high-quality samples of this material by following a sol-gel method based on heat treatment in both inert argon and oxygen atmospheres in order to compare their effect on the formation of the superconducting phase using X-ray powder diffraction. Magnetic measurements (DC and AC susceptibility) clearly demonstrate that, for the same concentration of Pr, the superconducting transition temperature markedly increases in all samples prepared in argon atmosphere, including pure Pr-123. (C) 2012 Elsevier B.V. All rights reserved.

Synthesis, structure and magnetic properties of cobalt(II) and copper(II) coordination polymers assembled by phthalate and 4-methylimidazole

New coordination polymers [M(Pht)(4-MeIm)2(H2O)]n (M=Co (1), Cu (2); Pht2−=dianion of o-phthalic acid; 4-MeIm=4-methylimidazole) have been synthesized and characterized by IR spectroscopy, X-ray crystallography, thermogravimetric analysis and magnetic measurements. The crystal structures of 1 and 2 are isostructural and consist of [M(4-MeIm)2(H2O)] building units linked in infinite 1D helical chains by 1,6-bridging phthalate ions which also act as chelating ligands through two O atoms from one carboxylate group in the case of 1. In complex 1, each Co(II) atom adopts a distorted octahedral N2O4 geometry being coordinated by two N atoms from two 4-MeIm, three O atoms of two phthalate residues and one O atom of a water molecule, whereas the square-pyramidal N2O3 coordination of the Cu(II) atom in 2 includes two N atoms of N-containing ligands, two O atoms of two carboxylate groups from different Pht, and a water molecule. An additional strong O–H⋯O hydrogen bond between a carboxylate group of the phthalate ligand and a coordinated water molecule join the 1D helical chains to form a 2D network in both compounds. The thermal dependences of the magnetic susceptibilities of the polymeric helical Co(II) chain compound 1 were simulated within the temperature range 20–300 K as a single ion case, whereas for the Cu(II) compound 2, the simulations between 25 and 300 K, were made for a linear chain using the Bonner–Fisher approximation. Modelling the experimental data of compound 1 with MAGPACK resulted in: g=2.6, |D|=62 cm−1. Calculations using the Bonner–Fisher approximation gave the following result for compound 2: g=2.18, J=–0.4 cm−1.

Syntheses, structures and magnetic properties of two copper(Ii) diphosphonates: [NH3(CH2)2NH3]2[Cu2(hedp)2]·H2O and [NH3CH(CH3)CH2NH3]2[Cu2(hedp)2] (hedp = 1-hydroxyethylidenediphosphonate)

This paper describes the syntheses and characterization of two new copper(II) diphosphonates: [NH3(CH2)2NH3]2[Cu2(hedp)2]·H2O (1) and [NH3CH(CH3)CH2NH3]2[Cu2(hedp)2] (2) (hedp = 1-hydroxyethylidenediphosphonate). Both compounds exhibit similar one-dimensional linear chain structures. The symmetrical {Cu2(hedp)2} dimers are connected by edge-shared {CuO5} square pyramids and form infinite chains. The Cu(II) ions are alternately bridged by O–P–O groups and O atoms. The Cu–O–Cu angles are 95.8(1) and 96.1(1)° for 1 and 2, respectively. Their magnetic properties show moderately strong antiferromagnetic interactions in both compounds.

A new bidimensional compound containing (μ-thiocyanate)(bpy)copper(II) molecules: synthesis, crystal structure and magnetic properties of [Cu(bpy)(NCS)2]n (bpy = 2,2'-bipyridyl)

The crystal structure of the first bidimensional copper(II) compound containing only thiocyanate as bridging ligands [Cu(bpy)(NCS) 2 ] n , where bpy=2,2'-bipyridyl, has been determined by X-ray diffraction on single-crystals. Two different environments for both types of copper(II) ions in the unit cell are apparent: a distorted octahedron and a square pyramid. A bidimensional structure with a deformed honeycomb-layer motif is formed, the bipyridyl ligands filling the interlayer space. The magnetic susceptibility data of the compound have been investigated between 280 and 1.8 K. The compound presents a very weak antiferromagnetic interaction that has been fitted by using the Bleaney-Bowers expression for a dimeric unit, whereby a J value of -1.01(1) cm - 1 (H=-JS 1 .S 2 ) and a g value of 2.08(1) have been obtained.

Biostratigraphic datums and magnetic properties of ODP Leg 178 sites

During Ocean Drilling Program (ODP) Leg 178, eight holes were drilled at three sites (1095, 1096, and 1101) on the continental rise along the western Antarctic Peninsula. The rise sediments proved to be good paleomagnetic recorders and provided continuous magnetostratigraphic records at all three sites. Biosiliceous microfossils, particularly diatoms and radiolarians, were present in the upper Miocene through lower Pliocene sections. In the upper Pliocene to Pleistocene sections, biosiliceous microfossils were rare but calcareous nannofossils and foraminifers were present. This paper summarizes the biostratigraphy and magnetostratigraphy of Leg 178 continental rise sites and is the first attempt at direct calibration of Antarctic biostratigraphic events to the geomagnetic polarity timescale in the Pacific sector of the Southern Ocean.

Physical, geochemical and magnetic properties of several ODP Leg 192 sites, Ontong Java Plateau

In this manuscript, we present the results of a physical properties investigation carried out on basaltic cores recovered from the four Leg 192 basement sites, focusing on the relationship between physical properties and alteration in basalts. Variations in physical properties in the Leg 192 basement sites closely resemble each other and reflect the amount of alteration and vein formation in the basement basalts. P-wave velocities, magnetic susceptibilities, and densities for the dense massive basalts are higher than those of more altered and heavily veined basalts. Porosity-dependent alteration is observed at Leg 192 basement sites: P-wave velocity displays a general decrease with increasing loss on ignition and potassium content. These trends are consistent with trends documented for typical alteration of oceanic crust and suggest that basalt alteration is largely responsible for the variation of the physical properties exhibited by rocks at Leg 192 basement sites. Our physical property data support the conclusion that only low-temperature seawater-mediated alteration occurred in the lava flows of the Ontong Java Plateau (OJP). This lack of higher-temperature hydrothermal alteration is consistent with the idea that the OJP basement sites are far from their eruptive vents.

Investigation on the structural and magnetic properties of sputtered TbFe2/Fe3Ga heterostructures

We have analyzed the structural and magnetic properties of as-grown and annealed [TbFe2/Fe3Ga]n heterostructures grown by sputtering. Evidence of the bcc structure in the Fe3Ga layers has been found. The diffraction peak related to this structure shifts to high angles with the annealing temperature. Also, we have observed a change in the microstructure of the Tb-Fe layers when the thickness layer is reduced in the as-grown heterostructures. Moreover, the Tb content is lower than 33% of the TbFe2 Laves phase and it depends on the layer thickness. The thermal treatments promote the increase of the Tb content, but only in the heterostructures with thick layers. The strong lattice mismatch between the Tb-Fe and Fe-Ga layers seems to prevent a complete Tb diffusion upon the annealing process. Thus, the crystallization of the TbFe2 Laves phase is inhibited in the heterostructures with thin layers, although our experimental results indicate the presence of potential magnetostrictive TbFeGa alloys

Electronic and optical properties of substitutional V, Cr and Ir impurities in Cu2ZnSnS4

The substitution of cation atoms by V, Cr and It in the natural and synthetic quaternary Cu2ZnSnS4 semiconductor is analyzed using first-principles methods. In most of the substitutions, the electronic structure of these modified CZTS is characterized for intermediate bands with different occupation and position within of the energy band gap. A study of the symmetry and composition of these intermediate bands is carried out for all substitutions. These bands permit additional photon absorption and emission channels depending on their occupation. The optical properties are obtained and analyzed. The absorption coefficients are split into contributions from the different absorption channels and from the inter- and intra-atomic components. The sub bandgap transitions are significant in many cases because the anion states contribute to the valence, conduction and intermediates bands. These properties could therefore be used for novel optoelectronic devices.