MAGNETORESISTIVE PROPERTIES OF MAGNETRON SPUTTERED La_(0.7)Sr_(0.3)MnO_3 THIN FILMS

摘要

La_(0.7)Sr_(0.3)MnO_3 (LSMO) films of variable thickness were deposited by magnetron sputtering on LaAlO_3 (100) substrate. The substrate ― film lattice mismatch causes changes in the microstructure and magnetoresistance. The substrate ― film lattice mismatch is compensated by large stress in LSMO layer at interface. With increasing of the film thickness this stress relaxes and upper film layer exhibits bulk value lattice parameters. Due to variable strain appeared in thin LSMO films different mag-netoresistive behaviour has been found. The sample with lowest thickness of 10 nm showed semiconducting behaviour. Epitaxial LSMO films of thickness 20 nm < d < 215 nm exhibit high Curie temperature up to Tc ～ 365 K and colossal magnetoresistance behaviour. High stressed film with metal ― insulator transition ～160 K showed both high negative magnetoresistance at T = 150 K and striking high positive magnetoresistance at T < 50 K.