R. N. Parmar

Thickness dependent swift heavy ion irradiation effects on electronic transport of (La0.5Pr0.2)Ba0.3MnO3 thin films

Electrical resistivity and magnetoresistance measurements on (La0.5Pr0.2)Ba0.3MnO3 thin films of 50 and 200nm thicknesses, irradiated by 200MeV Ag+15 ions, have been carried out. Before irradiation, all the films exhibit insulator-metal transition at a temperature (Tp) of ∼200K. After irradiation, both resistivity and Tp remain mostly unaffected in 50nm thin film but vary largely in 200nm thin films. This disparity in irradiation effect on these films is explained to arise from the interplay of columnar defect induced (i) enhancement in resistivity with increasing thickness of the film and (ii) local release of strain at the interfaces of low thickness films, which decreases resistivity.

Swift-heavy-ion-irradiation-induced enhancement in electrical conductivity of chemical solution deposited La0.7Ba0.3MnO3 thin films

Epitaxial thin films of La0.7Ba0.3MnO3 manganite, deposited using chemical solution deposition technique, were irradiated by 200MeV Ag+15 ions with a maximum ion dose up to 1×1012ions∕cm2. Temperature and magnetic-field-dependent resistivity measurements on all the films (before and after irradiation) reveal a sustained decrease in resistivity with increasing ion dose. A maximum dose of 1×1012ions∕cm2 suppresses resistivity by factors of 3 and 10 at 330K [insulator-metal (I-M) transition] and at 10K, respectively. On the other hand, with increasing ion dose, the magnetoresistance enhances in the vicinity of I-M transition but decreases at low temperatures. These results, corroborated by surface morphology of films, suggest that the origin of such properties lies in the irradiation induced improved crystallinity and epitaxial orientation, enhanced connectivity between grains and conglomeration of grains, which result in better conductivity at grain boundaries.

Growth-parameters-dependent magnetoresistance in pulsed-laser-deposited (La0.5Pr0.2)Ba0.3MnO3 thin films

Epitaxial thin films of (La0.5Pr0.2)Ba0.3MnO3 were deposited on LaAlO3 single-crystal substrates using pulsed laser deposition (PLD) technique with different growth parameters. Structural, surface morphological, electrical, and magnetotransport measurements on these films revealed that unoptimized growth parameters during the deposition using the third harmonic of a Q-switched Nd: YAG laser yielded structurally inhomogeneous epitaxial films having a columnar morphology, while the optimized growth parameters using an excimer laser during the PLD resulted in homogeneous epitaxial films with a smooth morphology. Interestingly, at a temperature of 5K, the films with unoptimized growth parameters showed a large high-field magnetoresistance (MR) of ∼90% while the films with optimized growth parameters showed a high-field MR of only ∼15%. It is contemplated that this exceptionally large MR in the unoptimized films might be due to the phase separation and coexistence of metallic and insulating phases.

NEUTRON DIFFRACTION STUDIES ON La2-xDyxCa2xBa2Cu4+2xOz SUPERCONDUCTORS

Structural studies on Dy-substituted La-2125 type superconductors have been carried out by neutron diffraction experiments at room temperature using a monochromatic neutron beam of wavelength (λ) = 1.249 Å. A series of samples with La2-xDyxCa2xBa2Cu4+2xOz stoichiometric composition, forx = 0.1–0.5, have been studied for their structural properties. A tetragonal Y-123 unit cell was taken as the starting model for the Rietveld analysis. All the samples fit into the starting model, with no structural transition taking place with increasing dopant concentration. The results of Rietveld analysis and structural properties will be discussed in detail.

Low Temperature Bond Valence Sum Study of La1.7 Dy0.3 Ca0.6 Ba2 Cu4.6 Oz Oxide Superconductors

Bond Valence Sum (BVS) calculations were performed on neutron diffraction (ND) data measured at 12, 35, 55, 75 and 300 K on one sample (x = 0.3), of a series of La2-xDyxCa2xBa2Cu4+2xOz (La-2125) compounds. ND experiments have been carried out to study the effect of temperature on structure and to relate it with the superconducting properties. The sample, La1.7Dy0.3Ca0.6Ba2Cu4.6Oz (LD3) has been reported earlier, and exhibits superconductivity at 68 K. In this paper we discuss BVS calculations carried out on low temperature neutron diffraction data.