The pressure, magnetic-field, and excess manganese effects on transport and magnetoresistance effect (MRE) are studied in both epitaxial films and bulk ceramics of the manganites (La0.7Ca0.3)1−xMn1+xO3−y (x=0–0.2). A comparison of the electrical behavior in both kinds of samples of similar composition at hydrostatic pressures of up to 1.8GPa and in magnetic fields of up to 8kOe is performed. The pressure and magnetic-field effects are shown to increase with increasing manganese content. Experimental data show that the effects of pressure and magnetic field on the temperatures of both the metal-insulator transition (TMD) and the MRE peak (TMR) are considerably stronger in the films than in the ceramics. The hydrostatic pressure increases TMD and TMR. It was shown that for both types of samples the magnetoresistance effect is affected in opposite ways by pressure and magnetic field. A direct correlation is established between TMD and conductivity bandwidth as well as between MRE and concentration of charge carriers at applied pressure. The differences in the values of pressure effect on resistance, MRE and TMD temperature in the films and ceramics are connected with both granular structure of ceramics and the oxygen nonstoichiometry in ceramic and film samples of the same content as well as with the film strain induced by lattice mismatch between the film and the substrate. The origin of pressure-magnetic-field effects is analyzed in the framework of the double exchange interaction and the small polaron hopping and variable-range hopping models.

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 (Δ R/R 0 ) were studied in La 0.7 Ca 0.3 Mn 1.0 O 3−δ based ceramics and single crystal films. A significant difference between the magnetoresistance peak temperatures ( T P ) observed in the ceramic and film samples is explained by their different deviations from the stoichiometry with respect to oxygen, that is, by a greater concentration of anion vacancies in the film perovskite structure. An increase in the magnetic field strength H and the pressure P leads to a decrease in the electric resistance R . The magnetoresistance grows with increasing field strength H and decreasing pressure P . A growth in the hydrostatic pressure leads to an increase in the T P value by 12 K for the ceramics and by 40 K for the films.

The effects of high hydrostatic pressures ( P ) and magnetic fields ( H ) in a broad temperature range ( T =77–325 K) on the electric resistance ( R ) and magnetoresistance (Δ R/R 0 ) was studied in laser-deposited La 0.7 Sr 0.1 Pb 0.2 MnO 3 single crystal films on (100)-oriented SrTiO 3 substrates. A maximum response to the P and H variations was observed in the temperature interval of phase transitions ( T =310–325 K). A growth in the pressure P leads to an increase in both R and Δ R/R 0 values, while an increase in the magnetic field strength H is accompanied by an increase in Δ R/R 0 and a drop in the electric resistance R of the single crystal films studied.

The effects of magnetic fields H=0–8 kOe and high hydrostatic pressures P=0–2.2 GPa on the resistivity ρ, magnetoresistive effect ΔR/R0, metal–semiconductor phase transition temperature Tms, and peak temperature Tp of the magnetoresistive effect are investigated over a wide range of temperatures T=77–350 K in a ceramic target and a laser film of the same cationic compound La0.7Mn1.3O3±δ. Increasing H and P leads to a decrease of the resistivity. The observed difference in ρ, Tms, and Tp between the ceramics and film samples is explained by the difference of their oxygen nonstoichiometry. The magnetoresistive effect decreases with increasing H and decreases with increasing P. The temperatures Tms and Tp of the ceramics and film increase with increasing P, but the effect is stronger in the film. The observation of two phase transitions in the ceramics (the main transition at Tms=250 K and an additional transition at Tms′=210 K) is explained by its mesoscopic inhomogeneity of the cluster type.