The T-P-H effects on the magnetoresistance of La0.7Ca0.3Mn1.0O3-delta ceramics and films

Effects of the temperature (T = 77-325 K), high hydrostatic pressures (P = 0-2.1 GPa), and magnetic fields (H = 0-8 kOe) on the electric resistance (R ) and magnetoresistance (DeltaR/R-0) were studied in La0.7Ca0.3Mn1.0O3 - de lta based ceramics and single crystal films. A significant difference betwe en the magnetoresistance peak temperatures (T-P) observed in the ceramic an d film samples is explained by their different deviations from the stoichio metry with respect to oxygen, that is, by a greater concentration of anion vacancies in the film perovskite structure. An increase in the magnetic fie ld strength H and the pressure P leads to a decrease in the electric resist ance R. The magnetoresistance grows with increasing field strength H and de creasing pressure P. A growth in the hydrostatic pressure leads to an incre ase in the T-P value by 12 K for the ceramics and by 40 K for the films. (C ) 2001 MAIK "Nauka/Interperiodica".