R. K. Das

Publications (3)8.89 Total impact

• Article: Susceptibility anisotropy in an iron arsenide superconductor revealed by x-ray diffraction in pulsed magnetic fields.

  J P C Ruff, J-H Chu, H-H Kuo, R K Das, H Nojiri, I R Fisher, Z Islam
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  ABSTRACT: In addition to unconventional high-T_{c} superconductivity, the iron arsenides exhibit strong magnetoelastic coupling and a notable electronic anisotropy within the a-b plane. We relate these properties by studying underdoped Ba(Fe_{1-x}Co_{x})_{2}As_{2} by x-ray diffraction in pulsed magnetic fields up to 27.5 T. We exploit magnetic detwinning effects to demonstrate anisotropy in the in-plane susceptibility, which develops at the structural phase transition despite the absence of magnetic order. The degree of detwinning increases smoothly with decreasing temperature, and a single-domain condition is realized over a range of field and temperature. At low temperatures we observe an activated behavior, with a large hysteretic remnant effect. Detwinning was not observed within the superconducting phase for accessible magnetic fields.
  Physical Review Letters 07/2012; 109(2):027004. · 7.37 Impact Factor
• Article: A novel approach for x-ray scattering experiments in magnetic fields utilizing trapped flux in type-II superconductors.

  R K Das, Z Islam, J P C Ruff, R P Sawh, R Weinstein, P C Canfield, J-W Kim, J C Lang
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  ABSTRACT: We introduce a novel approach to x-ray scattering studies in applied magnetic fields by exploiting vortices in superconductors. This method is based on trapping magnetic flux in a small disk-shaped superconductor (known as a trapped field magnet, TFM) with a single-crystal sample mounted on or at close proximity to its surface. This opens an unrestricted optical access to the sample and allows magnetic fields to be applied precisely along the x-ray momentum transfer, facilitating polarization-sensitive experiments that have been impractical or impossible to perform to date. The TFMs used in our study remain stable and provide practically uniform magnetic fields for days, which are sufficient for comprehensive x-ray diffraction experiments, specifically x-ray resonance exchange scattering (XRES) to study field-induced phenomena at a modern synchrotron source. The TFM instrument has been used in a "proof-of-principle" XRES study of a meta-magnetic phase in a rare-earth compound, TbNi(2)Ge(2), in order to demonstrate its potential.
  The Review of scientific instruments 06/2012; 83(6):065103. · 1.52 Impact Factor
• Source

  Available from: ArXiv

  Article: A robust but disordered collapsed-volume phase in a cerium alloy under the application of pulsed magnetic fields

  J. P. C. Ruff, Z. Islam, R. K. Das, H. Nojiri, J. C. Cooley, C. H. Mielke
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  ABSTRACT: We report synchrotron x-ray powder diffraction measurements of Ce0.8La0.1Th0.1 subject to pulsed magnetic fields as high as 28 Tesla. This alloy is known to exhibit a continuous volume collapse on cooling at ambient pressure, which is a modification of the gamma -> alpha transition in elemental cerium. Recently, it has been suggested on the basis of field-cooled resistivity and pulsed field magnetization measurements that the volume collapse in this alloy can be suppressed by the application of magnetic fields. Conversely, our direct diffraction measurements show a robust collapsed phase, which persists in magnetic fields as high as 28 Tesla. We also observe nanoscale disorder in the collapsed phase, which increasingly contaminates the high temperature phase on thermal cycling.
  09/2011;