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

The transport properties and magnetoresistive behavior of ferromagnetic La0.67Ca0.33MnO3-delta films deposited on Si and CeO2 buffered Si substrates has been investigated. The introduction of a CeO2 buffer layer between La0.67Ca0.33MnO3-delta films and Si substrates revealed a marked effect in shifting 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. The increase in magnetoresistance and decrease in the ferromagnetic transition 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 electrical conduction between Mn ions as a result of an increase in the Mn-O bond length due to decreased tensile stress in the a-b plane, which correspond qualitatively with Zener double exchange theory. [S0163-1829(98)02145-6].