• A M Umarji

      Articles written in Pramana – Journal of Physics

    • Spin fluctuation effects in substituted CeRu2Si2 and YbPd2Si2 alloys

      A M Umarji C Godart L C Gupta R Vijayaraghavan

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      Effects of chemical substitution in CeRu2Si2, a well-studied heavy fermion system and YbPd2Si2 have been investigated through magnetic susceptibility and x-ray diffraction in the systems CeRuxSi2, CeRu2−xOsxSi2, CeRu2Si2−xGex and YbPd2Si2−xGex. Replacing silicon by germanium generates normal chemical pressure effect, namely, Ce and Yb atoms in CeRu2Si2 and YbPd2Si2 became more and less magnetic respectively. With increasing Ge concentration, CeRu2Si2−xGex exhibits larger susceptibility at low temperature, goes to an antiferromagnetic state and finally becomes ferromagnetic. In YbPd2Si2−xGex, increasing Ge concentration drives Yb atoms to more divalent state. Electronic effects are more pronounced in CeRu2−xOsxSi2 though CeRu2Si2 and CeOs2Si2 have very nearly the same lattice parameters. It is conjectured that CeRu2Si2−xGex may be the first Ce-based heavy fermion having a magnetic ground state.

    • Effect of Sb substitution on the superconductivity of Bi2(Ca,Sr)n+1CunO4n+2 (n=1, 2 and 3) systems

      P Somasundaram A M Umarji

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      Effect of incorporation of Sb in place of Bi in the bismuth cuprate superconductors has been examined. The nominal compositions studied are MCa1·5Sr1·5Cu2O8+δ and MCa2Sr2Cu3O10+δ, whereM=Bi2−xSbx or Bi1·5−xSbxPb0·5. Different preparative routes such as the ceramic method, the matrix route as well as the melt route were employed to prepare the materials. No indication of either Sb entering the lattice or enhancement ofTc is noted from resistivity, magnetic susceptibility and microwave absorption measurements.

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