Stress and defect induced enhanced low field magnetoresistance and dielectric constant in La0.7Sr0.3MnO3 thin films

Colossal magnetoresistive manganite La0.7Sr0.3MnO3 (LSMO) films were prepared by pulsed laser deposition on three different single crystal substrates using different deposition parameters. Characterizations of their surface morphologies, structural, magnetic and magneto-transport properties show that films on MgO single crystal substrates contain higher amount of structural defects compared to those on SrTiO3 (STO) and NdGaO3 (NGO) substrates. Low deposition rate and thicker films give rise to polycrystallinity and grain boundaries. The films on MgO substrate showed a broad paramagnetic (PM) to ferromagnetic (FM) transition accompanied with metal–insulator transition (MIT) much below their Curie temperature (TC) indicating growth of strained structures due to large lattice mismatch (9%) between the substrate and the film. The deposited films on STO and NGO show least effect of substrate induced strain exhibiting sharper PM–FM transition and metallic behavior below TC. The magnetoresistance (MR) measured with 300 mT field clearly shows two contributions, one due to grain boundary tunneling and the other due to colossal MR effect. The highest low field MR effect of 17% was achieved for the film on MgO with the highest thickness and surface roughness indicating the presence of grain boundary related defects. Also a high dielectric constant was observed for the same film at room temperature up to 100 kHz frequency. Coexistence of defect induced large low-field MR and abnormally high dielectric constant can give rise to different exciting applications.