Abstract
Polycrystalline La 0.67A 0.33MnO z (A=Ca, Ba) thin films were successfully synthesized on quartz substrates by metal-organic decomposition. Some of the La 0.67(Ca 0.5Ba 0.5) 0.33MnO z films were deposited on quartz with a SrTiO 3 template layer (LCBMT). The porous structure of the films was observed by atomic force microscopy. It was found that all the films showed a broad peak effect of resistance under the zero field, over a temperature range of 77–302 K. Under a 10 kOe field, however, only La 0.67Ca 0.33MnO z films revealed a broad magnetoresistance (MR) peak. An enhanced MR effect was exhibited at low temperatures in all films, which was related to the porous structure of the films. LCBMT presented larger MR values below 180 K, than the La 0.67(Ca 0.5Ba 0.5) 0.33MnO z films without a template layer. The low-field MR effect was observed in all films at 77 K, but it weakened with increasing temperature, and disappeared near room temperature, which was attributed to the offset effect of the thermal hopping of carriers on the tunneling MR at high temperature.
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