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 magne toresistance (GMR) manganites by several orders of magnitude through d oping the Mn sites with a foreign cation is demonstrated for the first time, The perovskites Sm0.56Sr0.44Mn1-xFexO3 exhibit resistance maxim a characteristic of the transition from a ferromagnetic metallic (FMM) to a paramagnetic semiconducting state (PMSC) for 0 less than or equa l to x less than or equal to 0.03, It is shown that T-max decreases dr amatically 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 mo st 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 importa nt characteristic of the latter phase deals with the abrupt decrease o f its resistance by more than one order of magnitude through applicati on of a relatively low magnetic field, less than 0.2 T at 55 K. (C) 19 96 Academic Press, Inc.