CMR effect in electron-doped manganites Ca1-xSmxMnO3

The magnetic and transport properties of the Mn(IV)-rich perovskites Ca1-xSmxMnO3 have been investigated for x less than or equal to 0.20. These compounds exhibit very unusual magnetic behavior, especially for 0.14 less than or equal to x less than or equal to 0.20, where a peak is observed on the M(T) curves, whose temperature T-peak increases with x, whereas their height decreases. Moreover, colossal magnetoresistance properties are exhibited for the first time in these electron-doped systems, as shown for x = 0.15, which exhibits resistance ratios R-0/R-7T, of 10(2) and 10 at 50 and 100 K, respectively. These properties are interpreted in terms of a competition between ferromagnetism and antiferromagnetism, in connection with two opposing factors, namely, electron delocalization and charge ordering. (C) 1997 Academic Press.