Thin Film Growth and Magnetotransport Study of (La, Sr)MnO3

Abstract

ABSTRACTThin-film samples of La1-xSrxMnO3 (x = 0.20 – 0.30) were grown by pulsed-laser deposition using various target compositions, substrate materials, growth temperatures, oxygen partial pressures, and laser-pulse repetition rates. The crystal structure and the transport and magnetic properties of these films were then examined. Of the growth conditions, the oxygen partial pressure (Po2) had the greatest influence on the electrical and magnetic properties. Films grown under a low Po2 had a low ferromagnetic transition temperature (Tc) and a wide resistive transition width. None of the heat treatments done after growth improved these films’ quality. The film morphology was significantly affected by the substrate material. Our x-ray diffraction analysis and AFM measurements revealed that the films deposited on both MgO (100) and LaAlO3 (100) were epitaxially grown but contained defect structures. In contrast, grain-free thin films were epitaxially grown on the SrTiO3 (100) substrates. The surface roughness of films grown on SrTiO3 was less than 0.3 nm, even for films up to 150 nm thick. Under optimized growth conditions, as-deposited films for x ≥ 0.2 showed a sharp transition in resistivity at Tc. Magnetoresistance at far below Tc was as low as that reported for single-crystal sample. Since large magnetoresistance was often observed in polycrystalline samples and believed to be a grain boundary effect, these results indicate the high quality of the films grown on the SrTiO3 substrates.