STRUCTURE AND PROPERTIES OF THE PR1-XKXMNO3 PEROVSKITES (X=0-0.15)

The mixed-valence manganites Pr1-xKxMnO3 have been prepared up to maxi mum 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 monova lent potassium substitution generates mobile charge carriers and chang es gradually the magnetic ordering from the layered antiferromagnetism through canted arrangements to a pure ferromagnetism. The ferromagnet ic transition for sample with x greater than or equal to 0.10 is assoc iated with an anomaly in the temperature dependences of the resistivit y, thermopower, and a local maximum of the magnetoresistance. The insu lator-metal transition is absent up to 30% Mn4+ despite the expectatio ns based on the mean large cation size. An unexpected increase of the negative magnetoresistance is observed x = 0.15 at low temperatures wh ere the magnetization is already saturated. (C) 1997 Academic Press.