• V K Singh

      Articles written in Pramana – Journal of Physics

    • Mossbauer study of ferrite systems CoxMn1−xFe2O4 and NixMn1−xFe2O4

      V K Singh N K Khatri S Lokanathan

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      Mössbauer spectra of CoxMn1−xFe2O4 and NixMn1−xFe2O4 ferrites withx values ranging from 0·1 to 0·8 in steps of 0·1 have been recorded at room temperature. All spectra exhibit well-defined Zeeman hyperfine patterns. It has been observed that hyperfine field at Fe3+ nucleus increases more rapidly by nickel substitution than by cobalt substitution. This has been explained in terms of exchange interactions and cation distribution in the spinels. Hyperfine fields, isomer shifts and quadrupole splittings have been determined.

    • A Mössbauer study of hyperfine interaction in the systems CoxMn3−xyFeyO4 and NixMn3−xyFeyO4

      V K Singh R Chandra S Lokanathan

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      A Mössbauer study of systems CoxMn3−xyFeyO4 and NixMn3−xyFeyO4 for values ofx=0·1, 0·5, 1·0 andy ranging from 0·1 to 2·0 in steps of 0·2 have been made. At room temperature samples fory values ranging in between 0·1 to 0·5 exhibit paramagnetic behaviour while all spectra for values ofy between 0·6 to 0·8 show relaxation effects. Well-defined hyperfine Zeeman spectra are observed for all the samples withy>0·8 and resolved in two sextets corresponding to octahedral and tetrahedral site symmetries and a central doublet probably due to the presence of super-paramagnetic particles in the system. The hyperfine field at57Fe nucleus reduces with decreasing iron cobalt and nickel concentration. These observations have been explained in terms of site preference of cations and exchange interactions.

    • A Mössbauer study of octahedral site symmetries in systems Cox Mn3−xy FeyO4 and NixMn3−xyFeyO4

      V K Singh S Lokanathan

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      A Mössbauer study of cation distribution in systems Cox Mn3−xyFeyO4 and Nix Mn3−xy FeyO4 has been made. It has been found that in both systems all specimens withy<0.6 value exhibit quadrupole doublets corresponding to site symmetries Fe3+(I) and Fe3+(II) of octahedral site. As more and more cobalt or nickel is introduced into the matrix the intensity of the inner quadrupole doublet increases while on introducing iron that of the outer quadrupole doublet increases. After a certain concentration of iron the inner doublet starts becoming more intense. It is suggested that this arises possibly from the substitution of cations in the second co-ordination sphere of Fe3+(I) and Fe3+(II) sites. Fory>0.6 the Mössbauer spectra show relaxation effects.

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