Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.

31p-S-4 Giant Magnetoresistance in Magnetic Manganese Oxide with Intrinsic Antiferromagnetic Spin Structure

La0.67Ca0.33MnO3 thin films on Si (1 0 0) by DC magnetron sputtering technique using nanosized powder compacted target

The effect of ion irradiation on the proximity effect in YBa2Cu3O7−δ/La0.67Sr0.33MnO3 and YBa2Cu3O7−δ/SrTiO3/La0.67Sr0.33MnO3 heterostructures has been investigated using spin-polarized neutron reflectivity experiments. We demonstrate that the magnetization in the ferromagnetic (La0.67Sr0.33MnO3) layer at the interface is correlated with the suppression of the superconductivity in the YBa2Cu3O7−δ layer after irradiation, while the layer structure of the heterostructures remains intact. The evolution of the magnetization of the interfacial ferromagnetic layer studied as a function of temperature for both the irradiated heterostructures shows the absence of the proximity effect observed in the un-irradiated samples. The absence of a proximity effect is attributed to the suppression of the superconductivity, as seen in macroscopic magnetization measurements of the heterostructures after ion irradiation.

Suppression of the superconducting proximity effect in ferromagnetic-superconducting oxide heterostructures with ion-irradiation

A detailed investigation of the surface morphology of the pristine and swift heavy ion (SHI) irradiated La 0.7 Sr 0.3 MnO 3 (LSMO) thin film using atomic force microscope (AFM) is presented. Highly c -axis oriented LSMO thin films were grown on LaAlO 3 (1 0 0) (LAO) substrates by the pulsed laser deposition (PLD) technique. The films were annealed at 800 °C for 12 h in air (pristine films) and subsequently, irradiated with SHI of oxygen and silver. The incident fluence was varied from 1 × 10 12 to 1 × 10 14  ions/cm 2 and 1 × 10 11 to 1 × 10 12  ions/cm 2 for oxygen and silver ions, respectively. X-ray diffraction (XRD) studies reveal that the irradiated films are strained. From the AFM images, various details pertaining to the surface morphology such as rms roughness ( σ ), the surface rms roughness averaged over an infinite large image ( σ ∞ ), fractal dimension ( D F ) and the lateral coherence length ( ξ ) were estimated using the length dependent variance measurements. In case of irradiated films, the surface morphology shows drastic modifications, which is dependent on the nature of ions and the incident fluence. However, the surface is found to remain self-affine in each case. In case of oxygen ion irradiated films both, σ ∞ and D F are observed to increase with fluence up to a dose value of 1 × 10 13  ions/cm 2 . With further increase in dose value both σ ∞ and D F decreases. In case of silver ion irradiated films, σ ∞ and D F decrease with increase in fluence value in the range studied.

Effect of swift heavy ion irradiation on the surface morphology of highly c-axis oriented LSMO thin films grown by pulsed laser deposition

The effect of electron beam (e-beam) irradiation on the crystal structure and transport properties of polycrystalline samples of La0.8Sr0.2CoO3 (LSCO) and Pr0.8Sr0.2CoO3 (PSCO) cobaltites is reported in this communication. The of X-ray diffraction data reveals that the pristine and irradiated compounds of LSCO and PSCO samples are single phased having rhombohedral structure with R-3C space group. It is noticed that the crystal structure is preserved even after irradiation. Nonetheless the unit cell parameters are slightly altered when exposed to e-beam. The resistivity patterns of LSCO and PSCO samples demonstrate the occurrence of semiconducting behavior over the measured temperature range of 10–300 K. From the analysis of the temperature dependent resistivity data on the bulk samples, it is seen that small polaron hopping (SPH) mechanism is more dominating in the high temperature region of the pristine sample as compared to e-beam irradiated samples of LSCO and PSCO. The Seebeck coefficient (S) data of all the batches of LSCO and PSCO samples predominantly display positive values over a vast temperature region, indicating that holes are the dominant charge carriers. The investigation of S measurements confirms the validity of SPH mechanism in the high temperature region.

A systematic study on effect of electron beam irradiation on electrical properties and thermopower of RE0.8Sr0.2CoO3 (RE=La, Pr) cobaltites

Highly c -axis oriented, magnetoresistive thin films of La 0.7 Sr 0.3 MnO 3 deposited on LaAlO 3 (1 0 0) (LAO) substrates by pulsed laser deposition have been subjected to thermal annealing and subsequently to irradiation with swift heavy ions. While the as-deposited films show insulator metal transition T p at ∼265 K, the annealed films show metallic behavior over a wide temperature range viz. from 125 K to 400 K. We have investigated the effect of 90 MeV O 7+ ions and 200 MeV Ag 15+ ions on structural and electrical properties of these films. Dose values ranging from 1 × 10 12 to 1 × 10 14  ions/cm 2 of O 7+ ions and from 1 × 10 11 to 1 × 10 12  ions/cm 2 of Ag 15+ ions were used. The metal–insulator transition reoccurs in the irradiated films and the T p can be tailored to room temperature with irradiation dose value and energy of the ion. Attempt is made to comprehend this variation in T p on the basis of swift ion irradiation induced defects and related strain rather than change in oxygen content of the films.

S.S. Harchirkar

Papers

Swift ion irradiation induced changes in the structural and transport properties of La0.7Sr0.3MnO3 thin films