Stress effect and enhanced magnetoresistance in La0.67Ca0.33MnO3-delta films

The transport properties and magnetoresistive behavior of ferromagnetic La0 .67Ca0.33MnO3-delta films deposited on Si and CeO2 buffered Si substrates h as been investigated. The introduction of a CeO2 buffer layer between La0.6 7Ca0.33MnO3-delta films and Si substrates revealed a marked effect in shift ing the resistivity peak to low temperature and increasing the resistivity, in a similar way to that earlier observed in hydrostatic pressure studies. Enhanced magnetoresistance, with a Delta(rho)/(rho 0) ratio of 96% at 97 K in a magnetic field of 12 T, has been obtained in such film structures. Th e increase in magnetoresistance and decrease in the ferromagnetic transitio n temperature compared with unbuffered layers can be ascribed to a partial release in stress. The observed phenomena can be understood by the weakened ferromagnetic coupling and the decrease in transfer integral for electrica l conduction between Mn ions as a result of an increase in the Mn-O bond le ngth due to decreased tensile stress in the a-b plane, which correspond qua litatively with Zener double exchange theory. [S0163-1829(98)02145-6].