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31.
S. N. Mishra S. K. Mohanta S. M. Davane S. K. Srivastava 《Hyperfine Interactions》2010,197(1-3):71-75
We performed microscopic studies of the magnetic interaction in HOPG by measuring the hyperfine field of 19F using the time differential perturbed angular distribution (TDPAD) technique. The results show two hyperfine fields (Bhf) components: one varying strongly with temperature and saturating around 5 kG, while the other showing a maximum of 0.85 kG. The temperature dependence of Bhf does not show any signature of ferromagnetic ordering, but is reminiscent of enhanced paramagnetism. 相似文献
32.
Syntheses, structures, and magnetic properties of one mononuclear inclusion compound [CuIIL1 within (H2O)] (1) and three tetrametal systems of the composition [{CuIIL1}2{CuIIL1MII(H2O)3}]ClO4)2 (M = Cu (2), M = Co (3), M = Mn (4)) derived from the hexadentate Schiff base compartmental ligand N,N'-ethylenebis(3-ethoxysalicylaldimine) (H2L1) have been described. Compounds 1 and 2 crystallize in orthorhombic Pbcn and monoclinic P21/c systems, respectively, and the space group of the isomorphous compounds 3 and 4 is monoclinic C2/c. The water molecule in 1 is encapsulated in the vacant O4 compartment because of the hydrogen bonding interactions with the ether and phenolate oxygens, resulting in the formation of an inclusion product. The structures of 2-4 consist of the [CuIIL1MII(H2O)3]2+ cation and two mononuclear [CuIIL1] moieties. In the dinuclear [CuIIL1MII(H2O)3]2+ cation, the metal centers are doubly bridged by the two phenolate oxygens. The second metal center, MII (Cu in 2, Co in 3, and Mn in 4), in the [CuIIL1MII(H2O)3]2+ cation is pentacoordinated by the two phenoxo oxygens and three water molecules. Two of these three coordinated water molecules interact, similar to that in 1, with two mononuclear [CuIIL1] moieties, resulting in the formation of the tetrametal [{CuIIL1}2{CuIIL1MII(H2O)3}]2+ system that consists of the cocrystallized dinuclear (one) and mononuclear (two) moieties. Evidently, the cocrystallization observed in 2-4 is related to the tendency of a water molecule to be encapsulated in the vacant O4 compartment of the mononuclear [CuIIL1] species. In the case of 2, there are two independent [CuIIL1CuII(H2O)3]2+ units. The tau ((beta-alpha)/60, where beta and alpha are the largest and second largest bond angles, respectively) values in the pentacoordinated environment of the two copper(II) centers in 2 are 0.04 and 0.37, indicating almost ideal and appreciably distorted square pyramidal geometry, respectively. In contrast, the tau values (0.54 for 3 and 0.49 for 4) indicate that the coordination geometry around the cobalt(II) and manganese(II) centers in 3 and 4 is intermediate between square pyramidal and trigonal bipyramidal. The variable-temperature (2-300 K) magnetic susceptibilities of compounds 2-4 have been measured. The magnetic data have been analyzed in the model of one exchange-coupled dinuclear CuIIMII moiety and two noninteracting CuII centers. In all three cases, the metal ions in the dinuclear core are coupled by a weak antiferromagnetic interaction (J = -17.4 cm-1, -8 cm-1, and -14 cm-1 for 2, 3, and 4, respectively). The observation of a weak interaction has been explained in terms of the structural parameters and symmetry of the magnetic orbitals. 相似文献
33.
Nirmal Misra Mohendra Roy Dambarudhar Mohanta Kishor Kumar Baruah Amarjyoti Choudhury 《Central European Journal of Physics》2008,6(1):109-115
ZnO:Mn semiconductor quantum dots were prepared by solution casting led microemulsion route. Quantum dots of average size
∼2 nm were noticed in transmission electron micrographs. The present work highlights colour change phenomena (photochromic
effect) of quantum dots while subjected to photon illumination. The magneto-optic measurements e.g. magnetic field (H) vs angle of rotation (θ) show step like behavior and is ascribed to the quantum confinement effect of diluted magnetic ZnO:Mn nanostructures. Further,
underlying mechanism responsible for exhibiting photochromism and magneto-optic effects are also discussed.
相似文献
34.
Syntheses, structural characterization, crystal engineering, and variable-temperature magnetic study at fixed field strength of a novel dicyanamide bridged three-dimensional manganese(II)-nitronyl nitroxide compound, [Mn(II)(NIT-tz)(dca)(2)] (1), (NIT-tz = 2-(2-thiazole)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy-3-oxide, a new Ullman type radical) have been described. The compound crystallizes in the orthorhombic P2(1)2(1)2(1) space group with the following unit cell parameters: a = 11.015(2) A, b = 12.6134(14) A, c = 13.7652(9) A, and Z = 4. In this complex, the radical behaves as a bidentate chelating ligand, while four single end-to-end dicyanamide (dca) units construct the three-dimensional structure. Inside the structure, there exist diamond-shaped channels, spiral networks, and helical chains. Variable-temperature (5-300 K, 1 T) magnetic susceptibility data reveal the existence of antiferromagnetic interaction in this molecule. The magnetic behavior is explained by considering the exchange-coupled manganese(II)-radical system, which is subjected to the Mn(II)-dca-Mn(II) intermolecular interactions (H = -2JS(1).S(2) - 2zJ'S). The least-squares fitting of the data results J = -73 cm(-)(1), g = 1.99, and J' = -0.17 cm(-)(1) (z = 4). 相似文献
35.
The polymerization of acrylonitrile (M) initiated by the Ce(IV)-propane-1,2-diol (R) redox system has been studied in aqueous sulphuric acid under nitrogen in the temperature range 30 to 40°. The rate of polymerization is proportional to [M]2, [R] and [Ce(IV)]?1 and the rate of ceric ion disappearance is proportional to [R], [Ce(IV)]. The effects of certain salts, acid, solvent and temperature on both rates have been investigated. A kinetic scheme has been proposed, and various rate and energy parameters evaluated. 相似文献
36.
Phalguni Misra Rajesh Koner Malabika Nayak Sasankasekhar Mohanta John N. Low George Ferguson Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(10):m440-m444
Tetraaqua(18‐crown‐6)cerium(III) hexacyanoferrate(III) dihydrate, [Ce(C12H24O6)(H2O)4][Fe(CN)6]·2H2O, and tetraaqua(18‐crown‐6)neodymium(III) hexacyanoferrate(III) dihydrate, [Nd(C12H24O6)(H2O)4][Fe(CN)6]·2H2O, are isomorphous and isostructural in the C2/c space group, where the cations, which contain ten‐coordinate lanthanoid centres, lie across twofold rotation axes and the anions lie across inversion centres. In these compounds, an extensive series of O—H...O and O—H...N hydrogen bonds links the components into a continuous three‐dimensional framework. Triaqua(18‐crown‐6)lanthanoid(III) hexacyanoferrate(III) dihydrate, [Ln(C12H24O6)(H2O)3][Fe(CN)6]·2H2O, where Ln = Sm, Eu, Gd or Tb, are all isomorphous and isostructural in the P space group, as are triaqua(18‐crown‐6)gadolinium(III) hexacyanochromate(III) dihydrate, [Gd(C12H24O6)(H2O)3][Cr(CN)6]·2H2O, and triaqua(18‐crown‐6)gadolinium(III) hexacyanocobaltate(III) dihydrate, [Gd(C12H24O6)(H2O)3][Co(CN)6]·2H2O. In these compounds, there are two independent anions, both lying across inversion centres, and the lanthanoid centres exhibit nine‐coordination; in the crystal structures, an extensive series of hydrogen bonds links the components into a three‐dimensional framework. 相似文献
37.
R. Mohanta 《The European Physical Journal C - Particles and Fields》2000,16(2):289-294
Using the next-to-leading order QCD corrected effective Hamiltonian, scale and scheme independent Wilson coefficients, we
have estimated the branching ratio and CP violating asymmetries for the decay mode in the Standard Model using the framework of generalized factorization. The effects of nonfactorizable contributions
are taken into account by treating the effective no. of colors as a free parameter. The form factors are evaluated in the nonrelativistic quark model. The estimated branching ratio is
found to be which lies below the current experimental upper limit and the CP violating asymmetries are and .
Received: 15 February 2000 / Published online: 8 June 2000 相似文献
38.
39.
Hydroxyl free zinc oxide nanorods have been synthesized by a catalyst free surfactant based one-step solid state reaction
process. The powder X-ray diffraction studies reveal well defined wurtzite peaks due to crystalline ZnO, while optical absorption
spectra represent prominent exciton absorption and remarkable blueshift in the onset of absorption. As predicted by transmission
electron microscopy, the ZnO nanorods are ∼100 nm long and of ∼20 nm dia. Further, luminescence aspects of such nanorods are
studied for possible deployment in optoelectronics devices.
相似文献
40.
Development of a new lectron-recoil ion/photon coincidence setup for investigating some of the electron induced collision processes, such as electron bremsstrahlung, electron backscattering,
innershell excitation and multiple ionization of target atoms/molecules in bombardment of electrons having energies from 2.0
keV to 30.0 keV with solid and gaseous targets is described. The new features include the use of a compact multipurpose scattering
chamber, a time-of-flight spectrometer for detection of multiply charged target ions, a 45°-parallel plate electrostatic analyzer
for measuring energy and angle of the ejected electrons, a room temperature high resolution Si-PIN photo diode X-ray detector
for counting the collisionally induced photons, a coincidence data acquisition system consisting of a 200 MHz Pentium based
8K-multichannel analyzer and a standard network of a fast/slow coincidence electronics. In particular, the details of design,
fabrication and assembly of indigenous components employed in the setup are presented. Selected experiments planned with the
setup are mentioned and briefly discussed. A report on performance, optimization, efficiency, time resolution etc. of the
time-of-flight (TOF) spectrometer and that of the 45°-parallel plate electrostatic analyzer (PPEA) is presented. Test spectra
of electron-recoil ion coincidences, energy distribution of ejected electrons and characteristic plus non-characteristic X-ray
spectrum are illustrated to exhibit the satisfactory performance of the developed setup. 相似文献