Origin of magnetism and trend in T-c in Cr-based double perovskites: Interplay of two driving mechanisms

Hamiltonian constructed in a first principles manner, we explored the origin of magnetism and the T-c trend in Cr-based double perovskite series, Sr2CrB'O-6 (B' = W/Re/Os). Our study shows that the apparently puzzling T-c trend in Sr2CrB'O-6 (B' = W/Re/Os) series can be understood in terms of the interplay of the hybridization driven mechanism and the superexchange mechanism.

Interaction of Bacillus polymyxa with some oxide minerals with reference to mineral beneficiation and environmental control

Interaction of Bacillus polymyxa with calcite, hematite, corundum and quartz resulted in significant surface chemical changes not only of the cells but also in the minerals. Both the cell surfaces as well as quartz particles were rendered more hydrophobic after mutual interaction, whilst the rest of the minerals exhibited enhanced hydrophilicity after interaction with the bacteria. The bacteria were also observed to be capable of dissolving calcite, hematite and corundum and biosorbing the dissolved metal ions to varying extents. An excess of polysaccharides could be observed on biotreated calcite, hematite and corundum while the predominance of a protein-based metabolic product was evident on quartz surfaces. The utility of bioprocessing in the beneficiation of the above minerals through bioflotation and bioflocculation is demonstrated. (C) 1997 Elsevier Science Ltd.

Magnetism, charge ordering, and metal-insulator transition in the lanthanum manganites

We examine the magnetic and structural properties of the lanthanum manganite-based double-exchange magnets exhibiting colossal magnetoresistance. A model Hamiltonian containing the double-exchange, superexchange, and the Hubbard terms, with parameters obtained from density–functional calculations (Ref. 1), is studied within a mean-field approximation both at temperature T=0 and T>0 and with the effects of the magnetic field included. The phase diagrams we obtain with magnetic and charge-ordered phases enable us to examine the competition between the double- and superexchange terms as functions of doping and temperature. Our theoretical study provides a qualitative understanding of the phase diagram observed in the experiments. © 1997 American Institute of Physics.

Regular versus alternating (FeS4)(n) chains: Magnetism in KFeS2 and CsFeS2

We report crystal magnetic susceptibility results of two S = 1/2 one-dimensional Heisenberg antiferromagnets, KFeS2 and CsFeS2. Both compounds consist of (FeS4)(n) chains with an average Fe-Fe distance of 2.7 Angstrom. In KFeS2, all intrachain Fe-Fe distances are identical. Its magnetic susceptibility is typical of a regular antiferromagnetic chain with spin-spin exchange parameter J = -440.7 K. In CsFeS2, however, the Fe-Fe distances alternate between 2.61 and 2.82 Angstrom. This is reflected in its magnetic susceptibility, which could be fitted with J = -640 K, and the degree of alternation, alpha = 0.3. These compounds form a unique pair, and allow for a convenient experimental comparison of the magnetic properties of regular versus alternating Heisenberg chains.

Local environmental structures of Mo in the superionic conducting glass (AgI)(0.6)(Ag2MoO4)(0.4) by anomalous X-ray scattering

The anomalous X-ray scattering (AXS) method using Mo K absorption edges has been employed for obtaining the local structural information of superionic conducting glass having the composition (AgI)(0.6)(Ag2MoO4)(0.4). The possible atomic arrangements in the near-neighbor region of this glass were estimated by coupling the results with the least-squares variational analysis so as to reproduce the differential intensity profile for Mo as well as the ordinary scattering profile. The coordination number of oxygen around Mo is found to be about 4 at the distance of 0.180 mn. This implies that the most probable structural entity in the glass is the MoO4 tetrahedral unit which has been proposed based on infrared spectroscopy. The value of the coordination number of I- around Ag+ is estimated as 4.4 at 0.287 nm, suggesting an arrangement similar to that of crystalline or molten AgI.

Magnetism in MnPSe3: a layered 3d(5) antiferromagnet with unusually large XY anisotropy

The anisotropic magnetic susceptibilities of single crystals of the isostructural layered antiferromagnets, MnPS3 (T-N = 78 K) and MnPSe3 (T-N = 74 K), have been measured as functions of temperature. In both compounds, divalent manganese is present in the high-spin S = 5/2 state. The anisotropies in the susceptibilities of the two are, however, very different; while the susceptibility of MnPS3 is isotropic, that of MnPSe3 shows a large XY anisotropy, unusual for a manganese compound. The anisotropic susceptibilities are described by the zero-field spin Hamiltonian: H = DSiz2 - Sigma J(ij).(S) over right arrow (S) over right arrow(j) with the quadratic single-ion anisotropy term introducing anisotropy in an otherwise isotropic situation. The exchange J and the single-ion zero-field-splitting (ZFS) parameter D were evaluated using the correlated effective-field theory of Lines. For MnPSe3, J/k = -5.29 K and D/k = 26.6 K, while for isotropic MnPS3, J/k = -8.1 K. It is suggested that the large value of the ZFS parameter for MnPSe3 as compared to MnPS3 could be due to the large ligand spin-orbit contribution of the heavier selenium.

Combustion Synthesized Vanadia Rods for Environmental Applications

Rod-shaped V(2)O(5) was synthesized using the solution combustion technique, and the morphology of the compound was confirmed by TEM. Rods of an average diameter of 500 nm and length 3-6 times the diameter were obtained after the calcination of freshly prepared V(2)O(5) at 550 degrees C for 24 h. Pd metal nanoparticles of 20 nm size were deposited onto the rods using the wet impregnation technique. The as-synthesized, calcined and Pd impregnated V(2)O(5) were characterized by a wide variety of techniques including energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. These compounds were tested for CO oxidation, adsorption, and photocatalytic degradation of dyes. The 1% Pd/V(2)O(5) showed a high activity for CO oxidation, the as-synthesized compound showed activity for the adsorption of cationic dyes, whereas the calcined V(2)O(5) sample showed high rates of photocatalytic degradation of dyes. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 2215-2228, 2011

Tuning of dielectric properties and magnetism of SrTiO(3) by site-specific doping of Mn

Combining experiments with first-principles calculations, we show that site-specific doping of Mn into SrTiO(3) has a decisive influence on the dielectric properties of these doped systems. We find that phonon contributions to the dielectric constant invariably decrease sharply on doping at any site. However, a sizable, random dipolar contribution only for Mn at the Sr site arises from a strong off-centric displacement of Mn in spite of Mn being in a non-d(0) state; this leads to a large dielectric constant at higher temperatures and gives rise to a relaxor ferroelectric behavior at lower temperatures. We also investigate magnetic properties in detail and critically reevaluate the possibility of a true multiglass state in such systems.

Environmental audit of Municipal Solid Waste Management

The management of municipal solid waste has become an acute problem due to enhanced economic activities and rapid urbanisation. Increased attention has been given by the government in recent years to handle this problem in a safe and hygienic manner. In this regard, Municipal Solid Waste Management (MSWM) environmental audit has been carried out for Bangalore city through the collection of secondary data from government agencies, and interviews with stakeholders and field surveys. Field surveys were carried out in seven wards (representative samples of the city) to understand the practice and identify the lacunae. The MSWM audit that was carried out functional-element-wise in selected wards to understand the efficacy and shortfalls, if any, is discussed in this paper.

Form, Content, and Magnetism in Iron Oxide Nanocrystals

Monodisperse iron oxide nanocrystals with spherical and cubic morphologies, of comparable dimensions, have been prepared by the thermal decomposition of FeOOH. The lattice spacings of both forms agree with that of magnetite, Fe(3)O(4). The two, however, exhibit very different blocking temperatures. Nanocrystals of cubic morphology are superparamagnetic above 190 K while the spherical nanocrystals at a lower temperature, 142 K. The higher blocking temperatures in particles of cubic morphology are shown to be a consequence of exchange bias fields. We show that in the present iron oxide nanocrystals the exchange bias fields originate from the presence of trace amounts of wustite, FeO. A Reitveld refinement analysis of the X-ray diffraction patterns shows that nanocrystals of cubic morphology have a higher FeO content. The higher FeO content is responsible for the larger exchange bias fields that in turn lead to a higher blocking temperature for nanocrystals with cubic morphology.