COLOSSAL MAGNETORESISTANCE IN (LA0.7SN0.3)(2)MN2O7

A new manganite (La0.7Sn0.3)(2)Mn2O7 has been discovered that exhibits colossal magnetoresistance (CMR) near the Curie temperature and semic onductor-metal transition temperatures similar to that of La1-xDxMnO3 (D=Ca2+, Pb2+, etc.) or ABO(3) compounds. X-ray photoelectron spectra establish the presence of four valent Sn and Mn ions; thus the electri cal conductivity is n type rather than p type as for the ABO(3) materi al. Also, x-ray powder diffraction indicates that the crystal structur e is monoclinic. Magnetic susceptibility and Mossbauer spectra of Fe-5 7-doped samples have also been investigated. Although the resistivity of the iron-doped manganite is now larger, the CMR is actually increas ed.