• L C Gupta

      Articles written in Pramana – Journal of Physics

    • Crystallographic and magnetic phase transition in TlMnCl3

      R Vijayaraghavan M D Karkhanavala S D Damle L C Gupta U R K Rao

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      The results of our NMR, EPR and magnetic susceptibility measurements in the paramagnetic state of TlMnCl3 are reported here. The NMR paramagnetic shift of thallium is found to be small but positive. Mn2+ EPR line is exchange narrowed. The susceptibility measurements indicate an antiferromagnetic transition. The heat of crystallographic phase transition ΔH, in TlMnCl3 has been measured using differential scanning calorimetry. The crystallographic phase transition appears to be first order and ΔH is unusually low viz. 10 cal mole−1. In the case of KMnF3 ΔH, which is reported here for the first time, is determined to be 2 cal mole−1.

    • Nuclear quadrupole resonance studies of209Bi in Bi4(GeO4)3 and Bi4(SiO4)3

      K V Gopalakrishnan L C Gupta R Vijayaraghavan

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      Nuclear quadrupole resonance (NQR) of209Bi has been studied in Bi4 (GeO4)3 and Bi4 (SiO4)3 using a wide band coherence-controlled superregenerative oscillator-detector. All the four allowed (ΔMI=±1) transitions are observed. In both cases the electric field gradient (EFG) tensor is axially symmetric (η=0.0). The quadrupole coupling constante2qQ is measured to be 490.8±1 MHz and 470.4±1 MHz respectively. It is pointed out that the purely ionic model is inadequate to understand these results. With the available experimental accuracy and the strength of the applied electric field (∼ 6 KV/cm), no field-induced effects on the NQR spectrum could be observed in the case of Bi4 (SiO4)3.

    • A programmable digital pulse generator for pulsednmr spectroscopy

      R S Chaughule L C Gupta S M Telang

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      The pulse programmer generates highly stable pulses and is capable of producing various scheme of pulses (i.e. a given specific number of pulses with independently variable widths and separations) employed in pulsednmr spectroscopy. The construction and working of the programmer is described with reference to the two most commonly used schemes, namely, a two-pulse sequence and the Carr-Purcell sequence.

    • Spin fluctuation effects in substituted CeRu2Si2 and YbPd2Si2 alloys

      A M Umarji C Godart L C Gupta R Vijayaraghavan

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      Effects of chemical substitution in CeRu2Si2, a well-studied heavy fermion system and YbPd2Si2 have been investigated through magnetic susceptibility and x-ray diffraction in the systems CeRuxSi2, CeRu2−xOsxSi2, CeRu2Si2−xGex and YbPd2Si2−xGex. Replacing silicon by germanium generates normal chemical pressure effect, namely, Ce and Yb atoms in CeRu2Si2 and YbPd2Si2 became more and less magnetic respectively. With increasing Ge concentration, CeRu2Si2−xGex exhibits larger susceptibility at low temperature, goes to an antiferromagnetic state and finally becomes ferromagnetic. In YbPd2Si2−xGex, increasing Ge concentration drives Yb atoms to more divalent state. Electronic effects are more pronounced in CeRu2−xOsxSi2 though CeRu2Si2 and CeOs2Si2 have very nearly the same lattice parameters. It is conjectured that CeRu2Si2−xGex may be the first Ce-based heavy fermion having a magnetic ground state.

    • Specific heat anomaly in the 90 K superconductor HoBa2Cu3O7−y

      B K Basu S M Pattalwar R N Dixit S Y Shete A K Rajarajan L C Gupta R Vijayaraghavan

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      We report here the results of our heat capacityCp measurements on a monophasic material HoBa2Cu3O7−y. ΔCp/Tc, the jump inCp at the superconducting transition temperature (=91 K) of the material is measured to be 31 mJ/mol-K2.

    • 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.

    • Colossal magnetoresistance in layered manganite Nd2−2xSr1+2xMn2O7 (0 ≤ x ≤ 0.5)

      K Shah D K Aswal Ajay Singh L C Gupta S K Gupta V C Sahni

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      The layered manganite Nd2−2xSr1+2xMn2O7, with x varying between 0 and 0.5, has been synthesized using solid-state reaction method. We have found that Nd2−2xSr1+2xMn2O7 do not form the single-phase layered compound with A3B2O7 structure. Instead, mixtures of various phases, such as, orthorhombic perovskite, i.e., Nd1−zSrzMnO3, layered manganite and unreacted starting compounds, have been obtained. Except for x=0.4, which is found to be an antiferromagnetic insulator, all other x values yielded metal-insulator transition and ferromagnetic ordering.

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