Many physical characteristics including the Curie temperature T_C, the metal-insulator transition temperature T_MI, and resistance in doped lantanum perovskite manganites - materials having "colossal" magnetoresistance (CMR) can be changed to a considerable extent by internal chemical as well as by external physical pressure. The pressure and magnetic field effects on transport and magnetoresistance effect (MRE) have been studied in both the epitaxial films and ceramics of manganites with excess manganese (La_0.7Ca_0.3)_1-xMn_1+xO₃ (x = 0 - 0.2). A comparison of electrical behaviour in both kinds of ceramic and film samples of similar composition under the influence of hydrostatic pressure (up to 2 GPa) and magnetic field (up to 8 kOe) has been performed. The pressure as well as magnetic field decreases the resistivity in the region of the metal-insulator transition and shifts T_MI to higher temperatures. T_MI and MRE are shown to increase with increasing manganese content.
Experimental data show that the pressure and magnetic field effects on temperatures of both metal-insulator transition (T_MI) and MRE peak (T_MR) are considerably stronger in the films than in the ceramic samples. The linear increase of T_MI and T_MR by pressure was observed up to 2 GPa, and the pressure effect is stronger in the films. The main origin of the pressure-magnetic field effects is related to increasing double exchange (DE) interaction because of both the decrease of the unit cell volume and lattice distortions. The differences in the values of pressure effect on resistivity, MRE and metal-insulator transition temperatures in ceramics and in the films of the same content are due to a difference of both the oxygen nonstoichiometry and the film strain induced by lattice mismatch between the film and the substrate.

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