Showing papers by "K. Sethupathi published in 2006"

Electrical transport and morphological study of PLD-grown nanostructured amorphous carbon thin films

Abstract: Nanostructured carbon thin films have been actively investigated recently for their electroresistance (ER) properties. Furthermore, carbon films with nonlinear current?voltage (I?V) characteristics have potential application in field-emission devices. This has motivated us to study the effect of various growth parameters on the physical and morphological properties of carbon films grown by pulsed laser deposition (PLD). Carbon films have been deposited using a graphite target at different partial pressures of argon. The morphology of film surfaces deposited at various growth conditions was monitored using an atomic force microscope (AFM). AFM studies showed nanostructured grain growth with average grain size of about 80?90?nm. As the deposition time was decreased down to 1?min, the grain size was also found to decrease correspondingly. From Raman spectroscopic measurements an increase in the I(D)/I(G) ratio and a decrease in FWHM (G) clearly revealed the promotion of sp2 hybridization as the substrate temperature increased. All the films show semiconducting behaviour with the dominant conduction process being the three-dimensional (3D) variable range hopping (VRH) mechanism. Nonlinear I?V curves were obtained for carbon films deposited on p-type Si indicating diode-like behaviour. The most significant result of this study was the observation of a large electroresistance value.

Electrical transport properties of Dy0.5Gd4.5Si2Ge2

Abstract: Polycrystalline, Dy0.5Gd4.5Si2Ge2 compound (monoclinic, space group P21/a) has been synthesized and characterized. This compound orders ferromagnetically at ∼210 K (TC) followed by an antiferromagnetic-like transition at ∼21 K (TN). The electrical resistivity, ρ, follows T2 law in the ferromagnetically ordered state indicating the presence of dominant single magnon scattering. There is a pronounced increase of resistivity in the vicinity of antiferromagnetic transition. Thermoelectric power, S, indicates a slope change near TC and has T3 dependence at low temperatures.

Electrical and magnetotransport properties of Nd-based manganite nanoparticles

Abstract: Electrical and magnetotransport properties of nanocrystalline Nd07Sr03MnO3 sample having an average particle size of 45 nm have been studied The resistivity in paramagnetic regime follows Mott’s variable range hopping mechanism with an average hopping distance of about 21 A The observed magnetoresistivity (MR) has best been described by assuming that canted spins and defects are distributed all over the volume of the nanoparticle The MR could be quantitatively best fitted to spin-dependent hopping model, together with phase-separation phenomenon In this model, hopping barrier is proportional to the angle between the magnetic moments of the clusters The hopping barrier height is minimum when the moments are parallel to each other and is maximum when the moments are randomly oriented The fit yields a small cluster size of about two to three lattice constant dimensions in the paramagnetic (PM) phase and of about four to five lattice constants in the ferromagnetic (FM) phase The results indicate that