• Pran Kishan

      Articles written in Bulletin of Materials Science

    • Curie temperatures and 0°K magnetic moments of zinc-substituted lithium ferrites

      Pran Kishan D R Sagar S N Chatterjee L K Nagpaul K K Laroia

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      Because of their several attractive features including relatively high Curie temperatures, substituted lithium ferrites have become important for applications at microwave frequencies. Néel collinear arrangement of spins onA andB sublattices is unable to satisfactorily explain the 0°K saturation moments and the observed Curie temperatures of the zinc-substituted lithium ferrites, especially at concentrations of zincz>0·3 in the formula Li0·5−z/2ZnzFe2·5−z/2O4. Rosencaig’s localized canting model has been extended and used to compute 0°K magnetic moments and Curie temperatures of these ferrites with substitution levels up toz=0·7. Reasonably good agreement between the calculated and experimental values, both for the 0°K magnetic moments and the Curie temperatures, has been obtained using exchange parameters ratios based on the valuesJaa=−20°K,Jbb=−8°K andJab=Jba=−29°K.

    • Microwave ferrites for phase shifters

      Pran Kishan

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      The electronically steerable phased array radars (PARs) are finding extensive use in military, communication and civilian applications. A PAR system typically comprises a regular arrangement of a large number of phase controlled radiating elements. Ferrite-based phase shifters in various designs are employed in these systems operating at frequencies above 5 GHz due to their superior power rating and insertion loss characteristics. Under DRDO’s integrated missile programme considerable success has been achieved in the country on the development of ferrite materials, phase shifters and array system.

      The work done at SSPL on the development of ferrite materials for both X- and C-band phase shifters is described. The effect of various substituents in the chemical composition of the lithium-titanium ferrites and of the process parameters to evolve the grades with required magnetic, electrical and microstructural properties are discussed. The investigations carried out to enhance optimally the r.f. power handling capability of the material for meeting the desired specifications of the C-band phase shifter are also given.

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