Magnetoresistivity effect in ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_{3\mathrm{-}\mathrm{\delta }}{/\mathrm{P}\mathrm{r}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3\mathrm{-}\mathrm{\delta }}{/\mathrm{L}\mathrm{a}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_{3\mathrm{-}\mathrm{\delta }}$ trilayered films

The structure, magnetic and transport properties of high-quality ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_{3\mathrm{-}\mathrm{\delta }}/{\mathrm{Pr}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3\mathrm{-}\mathrm{\delta }}{/\mathrm{L}\mathrm{a}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_{3\mathrm{-}\mathrm{\delta }}$ (LPL) trilayered epitaxial films have been studied systematically. It was found that there is a transition from spin cluster-glass phase to ferromagnetic phase in the LPL films, and the resistivity decreases and $M-I$ transition temperature ${(T}_p)$ increases with the increase of middle-layered ${\mathrm{Pr}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3\mathrm{-}\mathrm{\delta }}$ (PCMO) thickness. It is interesting to notice that the maximum resistivity change $\Delta {R/R}_{\mathrm{L}\mathrm{P}\mathrm{L}\left(100\mathrm{}\mathrm{}\mathrm{n}\mathrm{m}\right)}$ is about -270% near 150 K, where $\Delta {R=(R}_{\mathrm{LSMO}}-R_{\mathrm{L}\mathrm{P}\mathrm{L}\left(100\mathrm{}\mathrm{}\mathrm{n}\mathrm{m}\right)}),$ $R_{\mathrm{LSMO}}$ and $R_{\mathrm{L}\mathrm{P}\mathrm{L}\left(100\mathrm{}\mathrm{}\mathrm{n}\mathrm{m}\right)}$ are the resistivities of ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}{\mathrm{MnO}}_{3\mathrm{-}\mathrm{\delta }}$ (LSMO) and LPL (100 nm) films, respectively, in zero-magnetic field. These results imply that there may exist an intrainteraction between the LSMO and PCMO layers in the LPL films, and that the middle-layered PCMO may act as a role of intramagnetic field and induce the change of the density of state in the LSMO gap. Magnetoresistivity values of the LPL films in a magnetic field of 0.75 T decrease with the increase of the thickness of middle-layered PCMO.