Comparison of pressure, magnetic-field, and excess manganese effects on transport properties of film and bulk ceramic La–Ca manganites

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 ...