Hydrostatic pressure effect on the metal-insulator transition in LaO0.7Ca0.3Mn1−x(Fe/Ge)xO3 perovskites

The temperature dependences of the resistivity of La 0.7 Ca 0.3 Mn 1−x Fe x O 3 and La 0.7 Ca 0.3 Mn 1−x Fe x O 3 (0 < × < 0.04) mixed crystals were studied under hydrostatic pressures up to 15kbar. The substitution of Fe for Mn results in an increase of the resistivity and a continuous decrease of the metal-insulator transition temperature T mi while the substitution of Ge for Mn leads to a more complicated T mi (x)-curve. In all cases T mi shifts under pressure with a rate between 1.6 and 2.9K/kbar and a correlation between T mi and its pressure derivative dT mi /dP is observed which is in accordance with the general trend of dT mi /dP versus T mi as derived for other manganites and is discussed in terns of a competition between superexchange and double exchange.