Structure and properties of the Pr1-xKxMnO3 perovskites (x=0-0.15)

The mixed-valence manganites Pr1-xKxMnO3 have been prepared up to maximum content of 30% Mn4+ (x = 0.15 in the ideal case) and investigated by the neutron diffaction and electric transport measurements. Similar to related systems with divalent alkali earths, the increasing monovalent potassium substitution generates mobile charge carriers and changes gradually the magnetic ordering from the layered antiferromagnetism through canted arrangements to a pure ferromagnetism. The ferromagnetic transition for sample with x greater than or equal to 0.10 is associated with an anomaly in the temperature dependences of the resistivity, thermopower, and a local maximum of the magnetoresistance. The insulator-metal transition is absent up to 30% Mn4+ despite the expectations based on the mean large cation size. An unexpected increase of the negative magnetoresistance is observed x = 0.15 at low temperatures where the magnetization is already saturated. (C) 1997 Academic Press.