• R G Kulkarni

      Articles written in Bulletin of Materials Science

    • Critical current density of the superconductor YBa1·5Ca0·5Cu3O7\t-\gd

      R B Jotania S M Joshi G J Baldha H H Joshi R G Kulkarni

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      The real and imaginary (lossy) components of a.c. susceptibility of high-Tc superconductor YBa1·5Ca0·5Cu3O7−δ were measured as a function of temperature for different a.c. fields and frequencies. From the lossy component of the a.c. susceptibility the transport critical current density and its temperature dependence have been computed on the basis of Kim’s critical state model.

    • Magnetic properties of magnesium-cobalt ferrites synthesized by co-precipitation method

      H H Joshi P B Pandya K B Modi N N Jani G J Baldha R G Kulkarni

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      The alternating current (a.c.) low field susceptibility vs temperature, magnetization and57Fe Mössbauer effect measurements are reported for the spinel solid solution series MgxCo1−xFe2O4 synthesized by a wet-chemical method before and after high temperature annealing. The observed features for the wet samples, such as the coexistence of paramagnetic doublet and magnetic sextets in Mössbauer spectra and lower saturation magnetization values confirm small particle ferrite behaviour. Especially, Mössbauer spectra of wet samples reveal the presence of superparamagnetic particles which exist simultaneously with ferrimagnetic regions in the materials well supported by a.c. susceptibility data. The high temperature annealing changes the wet-prepared ferrites into the ordered magnetic structure of ceramic ferrites.

    • Magnetic ordering in Mg1+xMnxFe2−2xO4 system

      N N Jani B S Trivedi H H Joshi G K Bichile R G Kulkarni

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      Magnetization measurements of the ferrite system Mg1+xMnxFe2−2xO4 were undertaken primarily to study variation of the saturation magnetization with manganese concentration and to gain information about the type of magnetic ordering. The observations indicate the existence of Yafet-Kittel (YK) type of magnetic ordering in this system which is well supported by results of Mössbauer effect measurements. A molecular field analysis of the YK spin ordering using the three-sublattice model is shown to explain the experimental data satisfactorily.

    • Magnetic properties of the mixed spinel Co1+xSixFe2−2xO4

      S S Shinde K M Jadhav G K Bichile Bimal S Trivedi R G Kulkarni

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      The structural and magnetic properties of the mixed spinel Co1+xSixFe2−2xO4 system for 0·1≤x≤0·6 have been studied by means of X-ray diffraction, magnetization, and Mössbauer spectroscopy measurements. X-ray intensity calculations indicate that Si4+ ions occupy only tetrahedral (A) sites replacing Fe3+ ions, and the added Co2+ ions substitute for (B) site Fe3+ ions. The Mössbauer spectra at 300 K have been fitted with two sextets in the ferrimagnetic state corresponding to Fe3+ at the A and B sites, forx≤0·3. The Mössbauer intensity data shows that Si possesses a preference for the A site of the spinel. The variation of the saturation magnetic moment per formula unit measured at 300 K with the Si content, is explained on the basis of Neel’s collinear spin ordering model forx≤0·3 which is supported by Mössbauer, and X-ray data. The Curie temperature decreases nearly linearly with increase of the Si content, forx=0·1–0·6.

    • Effect of calcium substitution on superconductivity and hole concentration in La1·5Ba1·5Cu3Oz

      Nikesh A Shah D G Kuberkar B T Savalia M R Gonal Ram Prasad R G Kulkarni

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      The superconducting properties of single phase La1·5−xCax+yBa1·5−yCu3Oz, 0·0≤x≤0·60 (LC) and 0·0≤y≤0·70 (CB), compounds with tetragonal triple-perovskite structure are studied, using X-ray diffraction for their resistivity, a.c. susceptibility, and oxygen-content. La1·5−xCaxBa1·5Cu3Oz (LC) samples, 0·15≤x≤0·60, are superconducting withTcR=0 between 40 and 74 K. With the increase inx, the oxygen content, hole concentration in the CuO2 layers as well as theTc increase. It is interesting to find that although the hole concentration and oxygen stoichiometry of the LaCa0·5+yBa1·5−yCu3Oz (CB) compounds increase with the increase iny, theTcR=0 remains nearly constant around 74 K fory=0·0−0·70. A correlation exists between theTc and the hole concentration for LC and CB compounds.

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