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  • 1. Garg, K. B.
    et al.
    Gaur, S. K.
    Singhal, R. K.
    Pal, P.
    Sekhar, B. R.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Carlson, S.
    Mechanism of quenching of superconductivity in the YBa2Cu3O7-delta system on substitution of Zn for Cu2010In: International Journal of Modern Physics B, ISSN 0217-9792, Vol. 24, no 14, p. 2135-2148Article in journal (Refereed)
    Abstract [en]

    Substituting Zn for Cu is known to rapidly quench superconductivity in the doped perovskites but the mechanism behind it is still not clearly understood. Single phase YBa2(Cu1-xZnx)(3)O7-delta (x=0.0 to 0.06) samples were synthesized and characterized using XRD, wet titration, resistivity, and ac susceptibility. Angle-integrated Valence Band Photo emission and Zn K-edge XAFS results clearly show that their oxygen stoichiometry (delta) changes on Zn substitution, there by adversely affecting the density of free charge carriers and hence the normal state resistivity and the T-c. However, the observed changes in the two happen to be too large to be accounted for solely on the basis of changes in the oxygen stoichiometry delta. We find that the Zn cation acts as a strong "impurity" scattering centre in the YBCO lattice and causes local lattice distortion (LLD). It consequently induces local magnetic moment, seen in our dc susceptibility measurements. It is thus a composite of (Delta delta), LLD and possibly also magnetic pair-breaking that is responsible for the rapid quenching of the super conductivity observed with Zn doping in this system.

  • 2.
    Garg, K B
    et al.
    Department of Physics, University of Rajasthan, Jaipur, India.
    Heinonen, M
    Dept of Material Science, Turku University, Finland.
    Nordblad, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Dalela, S D
    Department of Physics, Banasthali Vidyapeeth, Indien.
    Panwar, N
    Superconductivity and Cryogenics Division, National Physical Laboratory, New Delhi, Indien.
    Sen, V
    Superconductivity and Cryogenics Division, National Physical Laboratory, New Delhi, Indien.
    Agarwal, S K
    Superconductivity and Cryogenics Division, National Physical Laboratory, New Delhi, Indien.
    Sharma, Neha
    Department of Physics, university of Rajasthan, Jaipur, Indien.
    A comparative study of oxygen loss on in situ heating in PrMnO3 and BaMnO32011In: International Journal of Modern Physics B, ISSN 0217-9792, Vol. 25, no 9, p. 1235-1250Article in journal (Refereed)
    Abstract [en]

    We have thoroughly investigated the Oxygen loss in PrMnO3 and BaMnO3 the end members of the AMnO(3) system, on in situ heating in a reducing at This was done to drive some oxygen out from them and thus possibly alter the valence of the Mn cation. Sample characterization was done through X-ray diffraction and SEM measurements. The core-level photoemission point to oxygen loss from only BaMnO3 changing some of Mn4+ to Mn3+ in it, transfer of some spectral weight to the highly localized Fehrenbacher-Rice states and an increased Mn 3d-O 2p hybridization. Magnetization measurements show that at low temperatures, the samples depict a canted antiferromagnetic ordering.

  • 3. Haindl, S.
    et al.
    Kidszun, M.
    Onken, F.
    Mietke, A.
    Thersleff, Thomas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Lessons from oxypnictide thin films2013In: International Journal of Modern Physics B, ISSN 0217-9792, Vol. 27, no 4, p. 1330001-Article, review/survey (Refereed)
    Abstract [en]

    First experiments on the growth of oxypnictide F-doped LaFeAsO thin films indicated an incomplete normal-to-superconducting transition and offered a work programme challenging to overcome possible difficulties in their fabrication. In this regard the possibility of an all in-situ epitaxial growth appeared to be a matter of time and growth parameters. The following review clarifies that F-doped oxypnictide thin films are extremely difficult to grow by in-situ PLD due to the formation of very stable impurity phases such as oxyfluorides (LaOF) and oxides (La2O3) and the loss of stoichiometry possibly due to incongruent evaporation of the target or re-evaporation of volatile elements at the substrate surface. However, the review also demonstrates that the employed two-step fabrication process for oxypnictide thin films has been successfully applied in the preparation of clean polycrystalline as well as of epitaxial thin films. Fundamental investigations on the upper critical field, its temperature dependence and its anisotropy contributed to an understanding of multiband superconductivity in oxypnictides.

  • 4.
    Luo, Wei
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Fang, C. M.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Ahuja, Rajeev
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    NANOLAYERED MAX PHASES FROM ab initio CALCULATIONS2008In: International Journal of Modern Physics B, ISSN 0217-9792, Vol. 22, no 25-26, p. 4495-4499Article in journal (Refereed)
    Abstract [en]

    The advancement in new materials processing and fabrication techniques has made it possible to better control the atomistic level of structures in a way, which was not feasible only a decade ago. If one can couple this atomic control with a good understanding of the relationship between structure and properties, this will in the future lead to a significant contribution to the synthesizing of tailor-made materials. In this paper we have focused on, the structurally related nanolayered ternary compounds M(N+1)AX(N), (MAX) where N = 1, 2 or 3, M is an early transition metal, A is an A-group (mostly IIIA and IVA) element, and X is either C and/or N, which has attracted increasing interest owing to their unique properties. The general relations between the electronic structure and materials properties of MAX phases have been elaborated based on ab initio calculations

  • 5.
    Sanyal, Biplab
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Mookerjee, Abhijit
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
    Study of the electronic and structural properties of ZnO clusters2010In: International Journal of Modern Physics B, ISSN 0217-9792, Vol. 24, no 17, p. 3297-3309Article in journal (Refereed)
    Abstract [en]

    We present a systematic first-principle study of the structures, energetics and electronic structure of (ZnO)(n) clusters in the size range 1 <= n <= 12. We show that the planar ring structures are stable for n < 8, while spheroidal structures made out of rings of (ZnO)(3) and (ZnO)(2) are stable for n >= 8. We examine the binding energies and HOMO-LUMO gaps of the clusters and try to understand our results from simple physical ideas.

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