• A V Pimpale

      Articles written in Pramana – Journal of Physics

    • Doping and bond length contributions to Mn K-edge shift in La$_{1-x}$Sr$_{x}$MnO3 ($x=0-0.7$) and their correlation with electrical transport properties

      S K Pandey R Bindu Ashwini Kumar S Khalid A V Pimpale

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      The room temperature experimental Mn K-edge X-ray absorption spectra of La$_{1-x}$Sr$_{x}$MnO3 ($x = 0-0.7$) are compared with the band structure calculations using spin polarized density functional theory. It is explicitly shown that the observed shift in the energy of Mn K-edge on substitution of divalent Sr on trivalent La sites corresponds to the shift in the center of gravity of the unoccupied Mn $4p$-band contributing to the Mn K-absorption edge region. This correspondence is then used to separate the doping and size contributions to the edge shift due to variation in the number of electrons in valence band and Mn-O bond lengths, respectively, when Sr is doped into LaMnO3. Such separation is helpful to find the localization behaviour of charge carriers and to understand the observed transport properties of these compounds.

    • A high resolution powder diffractometer using focusing optics

      V Siruguri P D Babu M Gupta A V Pimpale P S Goyal

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      In this paper, we describe the design, construction and performance of a new high resolution neutron powder diffractometer that has been installed at the Dhruva reactor, Trombay, India. The instrument employs novel design concepts like the use of bent, perfect crystal monochromator and open beam geometry, enabling the use of smaller samples. The resolution curve of the instrument was found to have little variation over a wide angular region and a $\Delta d/d \sim 0.3%$ has been achieved. The instrument provides sample environment of very low temperatures and high magnetic fields using a 7 Tesla cryogen-free superconducting magnet with a VTI having a temperature range of 1.5–320 K. The special sample environment and high resolution make this neutron powder diffractometer a very powerful facility for studying magnetic properties of materials.

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