Dr Dharmalingam Prabhakaran

Abstract:

We report measurements and analysis of the magnetic critical phenomena in a single crystal of La0.875Sr0.125MnO3. The critical exponents associated with the ferromagnetic transition have been determined from ac susceptibility and dc magnetization data. Techniques like the Kouvel-Fischer plots, the modified Arrots plots, and the critical isotherm analysis were used for this purpose. The values of the exponents γ, β, and δ obtained are found to match very well with those predicted for the three-dimensional Heisenberg model. Our results are consistent with recent numerical calculations and suggest that though the double exchange interaction is driven by the motion of conduction electrons, the effective magnetic interaction near the transition is renormalized to a short range one. © 2003 The American Physical Society.

Abstract:

The spin ordering of La3/2Sr1/2NiO4 was investigated by magnetization measurements and by unpolarized and polarized-neutron diffraction. Spin ordering with an incommensurability ε≈0.445 is observed below TSO∼80 K. On cooling, a spin reorientation is observed at 57±1 K, with the spin axes rotating from 52° ±4° to 780°±3°.

Abstract:

We report the growth of single crystals of La1-xSrxMnO3 (x = 0.0-0.3) by the floating-zone technique in an image furnace under high argon pressure (6-8 atm). Ail excess of Mn in the polycrystalline starting material was used to compensate for the evaporation during growth. single crystals of diameter 8 mm and length 70 mm have been obtained. The phase purity, composition and quality of the crystals were analysed by X-ray diffraction and electron probe microanalysis. We discuss the effect on the crystal growth of varying the amount of Mn excess and of the composition of the growth atmosphere. We also present magnetization and resistivity data for a few of the samples. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract:

We report on an investigation into the growth of large, high-quality single crystals of La2-xSrxNiO4+ (x = 0-0.5) by the floating zone technique. The results of attempts to grow crystals in different atmospheres are discussed. The oxygen non-stoichiometry (delta) of the as-grown crystals is found to decrease with the Sr substitution level. Magnetic and electrical transport measurements on the crystals are reported. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract:

The present work investigates the texturing and superconducting properties of Sm substituted Bi2Sr2CaCu2O8+δ (Bi-2212) crystals grown by the floating zone technique. The texturing nature of Bi-2212 was quantified by Xray diffraction and by scanning electron microscopic studies. The texturing nature varies with respect to the 'Sm' concentration. Superconductivity studies were carried out by the resistivity technique and the transition temperature increases from 78K to 85K (for x=0.2) and decreases for higher concentration. The c-lattice parameter decreases with Sm substitution. © 2000 Elsevier Science B.V All rights reserved.