• E V Sampathkumaran

      Articles written in Bulletin of Materials Science

    • ESCA studies of some mixed-valence rare-earth intermetallics

      B D Padalia Varsha Prabhawalkar P D Prabhawalkar E V Sampathkumaran L C Gupta R Vijayaraghavan

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      ESCA (or XPS) studies of some rare-earth intermetallics were carried out using ESCA (3) Mark II and ‘ESCALAB’ machines from V G Scientific. The mixed valence nature of EuCu2Si2 and EuNi2P2 intermetallic compounds has been established. The 3d core-level photoemission spectra of Eu in EuCu2Si2 and EuNi2P2 exhibit two sets of structures corresponding to two different valence states of the rare-earth ions. Each of these sets shows simple spin-orbit splitting. The replicate splitting measured by us agrees well with those calculated by Herbst and Wilkins. The 3d core-level photoemission spectra of Eu is free from the multiplet splitting and satellite structure. The importance of 3d core-level photoemission studies in the understanding of valence fluctuation phenomenon has been emphasized.

    • Influence of transition metals substitution on the superconductor Bi4Ca3Sr3Cu4Oy

      E V Sampathkumaran R Vijayaraghavan

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      The results of our investigation on the specimens Bi4Ca3Sr3Cu4−xTxOy (T=Fe, Co, Ni,x⩽0.5) synthesized in air are presented. Fe and Co substituents result in the formation of Bi2Sr2CuOy-type of phase, with considerable depression ofTc of the main phase. However, Ni is completely soluble with Cu in this concentration range without significant depression of superconducting transition temperature (Tc). This difference in the solubility behaviour of Fe and Co on the one hand and Ni on the other is explained taking into account ionic charge and coordination number mismatches.

    • Electron paramagnetic resonance studies in the oxides Bi2Sr2Ca1−xGdxCu2Oy

      M D Sastry E V Sampathkumaran R M Kadam

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      We have recently reported our results on magnetic susceptibility and microwave absorption studies on Bi2Sr2Ca1−xGdxCu2Oy and Bi2Sr2Ca1−xYxCu2Oy. In the present work two important observations of these investigation, viz, the dependence ofTc on Gdconcentration and the absence of EPR-signals of Gd and Cu, are considered in greater detail. It is suggested that the microwave absorption by fluxon lattice might be playing one of the important and effective pathways for electron spin relaxation resulting in nonobservation of EPR signals.

    • Mössbauer studies of Gd-doped bismuth-based ceramic superconductors

      E V Sampathkumaran G Wortmann G Kaindl

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      The results of155Gd Mössbauer studies (above 1·5K) of the oxides, Bi3·5Gd0·5Ca3Sr3Cu4Oy and Bi2Sr2Ca1−xGdxCu2Oy (x=0·25 and 0·5) are reported. The observed electric quadrupolar split resonance patterns suggest that Gd ions prefer to occupy Ca site in both series. The spectral features give evidence for paramagnetic relaxation of isolated Gd ions at low temperatures.

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