• N S Satya Murthy

      Articles written in Pramana – Journal of Physics

    • Non-spherical magnetic moment in MnAlGe

      S K Paranjpe S R Tendulkar L Madhav Rao N S Satya Murthy

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      The magnetic structure factors of MnAlGe (space groupP4/nmm) measured with polarised neutrons have been expressed in terms of the magnetic moment of the Mn atom (site symmetry tetrahedral with tetragonal distortion), the Bessel transforms 〈jn〉 of the Mn radial functions and the fractional occupancies of the moment density in the various crystal field orbitals. The measured structure factors were least-squares fitted with the theoretical expression involving 〈jn〉 appropriate to the Mn0, Mn+ and Mn2+ atoms. The best fit was got using Mn0 transforms, yielding 1·45µB as the Mn magnetic moment. The fractional occupancies of the moment density in the crystal field orbitalsA1g,B1gEg andB2g were obtained. This analysis shows the magnetic moment to be highly non-spherical with a large fractional occupancy (38%) in theA1g orbital directed along the tetragonal axis while the fractional occupancies ofB1g andB2g are found to be 31% and 30% respectively. The fractional occupancy of the moment in theEg orbital directed towards the Ge and Al atoms is very low (1%). The spatially averaged moment density of Mn in MnAlGe is more diffuse than that of Mn I and Mn II in isostructural Mn2Sb.

    • A polarised neutron study of magnetic moment density in Cu2MnAl

      V C Rakhecha R Chakravarthy N S Satya Murthy

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      A polarised neutron study of the ferromagnetic Heusler alloy Cu2Mn0.863Al1.057 has been made. It has been concluded that the magnetic moment density is primarily situated on the Mn ions. On assigning the Mn-moment value, the observed magnetic form factor is found to be in good agreement with the Mn2+ free ion form factor calculated by Watson and Freeman. A slight asphericity has been observed in the moment density. It is estimated that there are about 3% excess 3d-electrons in the Eg states compared to spherical distribution. There is evidence of a very small positive polarisation of the Cu atoms. No appreciable conduction electron polarisation is found.

    • Magnetic moment distributions and form factors in ferromagnetic nickel-ruthenium alloys

      R Chakravarthy L Madhav Rao N S Satya Murthy

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      Using polarised neutrons, the full three-dimensional magnetic structure amplitudes in the Ni1−c Ruc single crystals forc = 0·027, 0·033 and 0·046 were measured. Moment density maps in various portions of the Wigner-Seitz cell were obtained. It is seen from these maps that unlike Ni-based alloys with 3d impurities, the introduction of Ru to the Ni matrix produces extensive perturbations in the diffuse moment density, giving rise to a netpositive diffuse moment which tends to increase with Ru concentration. The asphericity of the host moment at first increases and then decreases with increasing Ru content. Another significant outcome of the present study is the evidence for the reversal of the sign of the Ru moment, from negative to positive, obtained by comparing the shape of the spherical site form factors of the three-alloy concentrations with the Ni spherical form factor itself. The sign reversal of the impurity moment is confirmed by the form factor analyses. Strong local environmental effects seem to play a major role in this alloy system.

    • Thermal neutron polarisation

      N S Satya Murthy L Madhav Rao

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      The basic principle for the production of polarised thermal neutrons is discussed and the choice of various crystal monochromators surveyed. Brief mention of broad-spectrum polarisers is made. The application of polarised neutrons to the study of magnetisation density distributions in magnetic crystals, the dynamic concept of polarisation, principle and use of polarisation analysis, the neutron spin-echo technique are discussed.

    • Neutron diffraction studies of transition metal nitrides

      N S Satya Murthy S K Paranjpe Marsongkohadi Kurniadi Sumaamidjaja M R L N Murthy

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      The magnetic structures of Fe4N and Mn4N have been redetermined using neutron diffraction. The magnetic form factors, obtained from polarised neutron data have been shown to be different for the face-centred and corner atoms. A qualitative explanation of the structures of Fe4N and Mn4N has been provided from the shapes of the magnetic form factors.

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