• K N Shrivastava

      Articles written in Proceedings – Section A

    • Electron spin resonance of Mn2+ in NaCl single crystal and lattice defects

      K N Shrivastava Putcha Venkateswarlu

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      The electron spin resonance spectra of Mn2+ in NaCl single crystals are investigated in detail. Seven different spectra (I, II, III1, III2, IV, V and VI) are observed. The spectra I–IV are the same as those observed by earlier workers, while the spectra V and VI are observed here for the first time. The local symmetry at the paramagnetic ion is orthorhombic for the spectra IV and V and tetragonal for the spectrum VI about the crystallographic [001] direction. The properties of the spectrum IV are explained in terms of an associated pair Mn2+: O22− with O22− molecular ion at the nearest neighbour anion site in the [001] direction with its internuclear axis in the (001) plane. The spectrum V is assigned to the associated pair Mn2+: O22− coupled with a nearby cation vacancy in the [001] direction and the spectrum VI to Mn2+ ion associated with OH ion at the anion site in the [001] direction with a probable second neighbour cation vacancy. All the observed spectra are analysed in terms of the parameters of the usual spin-Hamiltonian.

    • Forbidden hyperfine transitions in electron spin resonance of Mn2+ in NaCl single crystal

      K N Shrivastava Putcha Venkateswarlu

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      Forbidden hyperfine transitions are observed in the electron spin resonance spectrum of divalent Mn55 ion in NaCl single crystal for a particular associated pair. From the measurements of the M = + 1/2 → −1/2, Δm = ± 1 transitions the parametersQ′ and Q″ of the nuclear electric quadrupole part of the spin-Hamiltonian Ho = Q′ [Iz2 − 1/3 I (I + 1)] + Q″ (Ix2−Iy2) are found to be + 1.70 × 10−4 cm.−1 and +0.16 × 10−4 cm.−1 respectively.

    • Paramagnetic resonance of Mn2+ in KNO3 single crystal: Motional effects

      K N Shrivastava Putcha Venkateswarlu

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      The electron paramagnetic resonance of Mn2+ in KNO3 single crystal is investigated over a temperature cycle through transition temperatures. The hyperfine coupling constant, A, half width,Δ H, and the line intensity, I, are found to show sudden changes at the transition temperature, at whichα-KNO3 changes intoβ-KNO3. The lines are much sharper in the high temperatureβ-phase than inα-phase of the crystal. They are explained, qualitatively, in terms of structure change and rotation of NO3 ions. The spectra in the two phases,α andβ, are analysed in terms of usual spin-Hamiltonian. A search of metastableγ-phase is also made and probable indications for the same are found.

    • Effect of temperature and time on paramagnetic resonance of Mn2+ in NaCl single crystal

      K N Shrivastava Putcha Venkateswarlu

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      Exchange of intensities among various spectra of Mn2+ in NaCl single crystal, corresponding to Mn+2 ion associated with various point defects, is described as a function of temperature and time. The variation of line width with temperature is discussed. The fine structure parameter D for a particular spectrum is measured with temperature and is shown to behave like D=D0 (1+bT+cT2). Thermal formation of new complexes and their lifetimes are discussed. A new short-lived complex is found and a model for the same is suggested.

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