• R Nagarajan

      Articles written in Pramana – Journal of Physics

    • Superconductivity in layered nickel oxides

      C N R Rao A K Ganguli R Nagarajan

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      Likely presence of superconductivity in layered nickelates of K2NiF4 structure is pointed out.

    • Unusually large shift in low-temperature susceptibility peak of Fe2.8Ti0.2O4 with frequency

      C Radhakrishnamurty S D Likhite R Nagarajan

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      The temperature dependence of magnetic susceptibility,x, of titanomagnetites (Fe3−xTixO4, 0⩽x⩽0.2) at different frequencies in the range of 13 Hz to 117 kHz is reported. Whereas the position of thex-peak of Fe3O4 at 120 K shows no significant shift over this frequency range, that of Fe2.8Ti0.2O4 shifts from 70 K at 13 Hz to 115 K at 117 kHz. This seems to be the first observation of such large shift in the position of ax-peak observed at low-temperatures is attributed to the occurrence of an isotropic point (temperature at which first order anisotropy constantK1=0) associated with change in crystal structure. In such a case a shift inx-peak with frequency is not expected normally. Thus, the observed large shift in the position ofx-peak with frequency is an unusual phenomenon and some of its repercussions are discussed.

    • Foreword

      R Pinto R Nagarajan

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    • Possible coexistence of superconductivity and magnetic order in NdPt2B2C

      S K Dhar A D Chinchure E Alleno C Godart L C Gupta R Nagarajan

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      Coexistence of superconductivity and magnetic order has been one of the exciting aspects of the quaternary borocarbide superconductors, So far, RNi2B2C (R=Tm, Er, Ho and Dy) are the only known magnetic superconductors in this family. Here, we present our resistivity, magnetization and heat capacity studies on NdPt2B2C (nominal composition, NdPt1.5Au0.6B2C and NdPt2.1B2.4C1.2). We find superconductivity in both samples with Tc,onset ∼ 3 K. Bulk magnetic order is found to occur below 1.7 K. We suggest that NdPt2B2C is a possible magnetic superconductor.

    • Modification of magnetic anisotropy in metallic glasses using high-energy ion beam irradiation

      KV Amrute UR Mhatre SK Sinha DC Kothari R Nagarajan D Kanjilal

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      Heavy ion irradiation in the electronic stopping power region induces macroscopic dimensional change in metallic glasses and introduces magnetic anisotropy in some magnetic materials. The present work is on the irradiation study of ferromagnetic metallic glasses, where both dimensional change and modification of magnetic anisotropy are expected. Magnetic anisotropy was measured using Mössbauer spectroscopy of virgin and irradiated Fe40Ni40B20 and Fe40Ni38Mo4B18 metallic glass ribbons. 90 MeV 127I beam was used for the irradiations. Irradiation doses were 5×1013 and 7.5×1013 ions/cm2. The relative intensity ratios D23 of the second and third lines of the Mössbauer spectra were measured to determine the magnetic anisotropy. The virgin samples of both the materials display in-plane magnetic anisotropy, i.e., the spins are oriented parallel to the ribbon plane. Irradiation is found to cause reduction in magnetic anisotropy. Near-complete randomization of magnetic moments is observed at high irradiation doses. Correlation is found between the residual stresses introduced by ion irradiation and the change in magnetic anisotropy.

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