Increase of the GMR ratios up to 10(6) by iron doping in the manganite Sm0.56Sr0.44MnO3

The possibility of increasing the resistance ratios of the giant magnetoresistance (GMR) manganites by several orders of magnitude through doping the Mn sites with a foreign cation is demonstrated for the first time, The perovskites Sm0.56Sr0.44Mn1-xFexO3 exhibit resistance maxima characteristic of the transition from a ferromagnetic metallic (FMM) to a paramagnetic semiconducting state (PMSC) for 0 less than or equal to x less than or equal to 0.03, It is shown that T-max decreases dramatically as x increases, from 130 K for x = 0 to 55 K for x = 0.03; phases with x greater than or equal to 0.04 are semiconductors, The most spectacular effect is observed for the composition Sm0.56Sr0.44Mn0.97Fe0.03O3, which exhibits a T-max of 55 K and a resistance ratio R(0)/R(H) of 8 x 10(5) at 55 K in a magnetic field of 5 T, Another important characteristic of the latter phase deals with the abrupt decrease of its resistance by more than one order of magnitude through application of a relatively low magnetic field, less than 0.2 T at 55 K. (C) 1996 Academic Press, Inc.