Abstract Recently, the large magneto-resistance effects in epitaxial manganite thin films has interested in the doped manganite perovskite materials for magnetic random access memory (MRAM) and read-head application. The relation between the magneto-resistance and microstructure of the colossal magneto-resistance materials has been evaluated in this study. Different thickness of La0.67Ca0.33Mn03 (LCMO) thin films were grown on (001) MgO and (001) SrTi03 (STO) substrates at growth temperature 750 degree C with RF magnetron sputtering technique, respectively. These substrates provide two different lattice-mismatch conditions for the LCMO films (+9% for MgO and +1% for STO). The crystal structure of LCMO films were characterized with X-ray diffraction (XRD), the surface morphology of LCMO films were observed by scanning electron microscope (SEM), the interface of microstructure between LCMO films and substrate were studied by transmission electron microscope (TEM), the thickness and chemical composition of LCMO films were determined by Rutherford backscattering spectrometer (RBS), and finally the resistance and I-M transition temperature were evaluated at temperature range from 77K to 300K. The results show that the epitaxial LCMO films with a superlattice structure were obtained on STO substrate and polycrystal structure of LCMO films were on MgO substrate due to larger lattice mismatch.. The transition temperature of magneto-resistance of LCMO thin film is quite sensitive with film thickness. The transition temperature increases with film thickness increased. When the film with thickness excess of 2000A, the transition temperature is nearly same as that of LCMO bulk material.. The existed strain and the microstructure of LCMO films are two important factors related with magnetic resistance and electrical properties of LCMO films.

Abstract Recent progress in oxide perovskite thin-film technology has led to the discovery of a large negative magnetoresistance in doped manganate perovskite thin films. These films may have potentials for magnetic random access memory (MRAM) and magnetic sensors. Therefore, the research of magnetoresistance has been attracted a lot of attentions. The magnetoresistance is directly related to the microstructure. In an application point of view, the ulta-thin film may be more appropriate compares with those utilizing with thicker films. In this paper, we report the detail results of electrical property of La0.67Ca0.33MnO3 (LCMO) films related with their microstructure. The La0.67Ca0.33MnO3 (LCMO) films were deposited on (001) STO substrate with RF sputtering technique. The working pressure was maintained at 100m torr and the growth temperature was kept at 750¢J. After growth the films was annealed at 850¢J for 1 hour in a 500 torr O2 annealing environment. The growth time was 3mins.¡B6mins. and 12mins. respectively. The crystal structure of LCMO films were characterized with X-ray diffraction (XRD). The surface morphology of LCMO films were observed by scanning electron microscope (SEM) and the interface of microstructure between LCMO films and STO substrate were investigated by transmission electron microscope (TEM). Finally the M-I transition temperature were evaluated with 4-point probe at the temperature range from 300K down to 77K. The results show that the LCMO films were amorphous when the growth time was in 3 mins. The microstructure of the film gradually became poly-crystal and had a (001) prefer orientation after the growth time increasing to 6 mins. The grain size of the 12 mins growth film was at 40-50 nm scale. The Curie temperature and magnetoresistance change of these films were increased as the degree of crystallization of these films became better.