Colossal magnetoresistance in (${\mathrm{La}}_{0.7}$${\mathrm{Sn}}_{0.3}$${)}_2$${\mathrm{Mn}}_2$${\mathrm{O}}_7$

A new manganite (${\mathrm{La}}_{0.7}$ ${\mathrm{Sn}}_{0.3}$ ${)}_2$ ${\mathrm{Mn}}_2$ ${\mathrm{O}}_7$ has been discovered that exhibits colossal magnetoresistance (CMR) near the Curie temperature and semiconductor-metal transition temperatures similar to that of ${\mathrm{La}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{D}}_{\mathrm{x}}$ ${\mathrm{MnO}}_3$ (D=${\mathrm{Ca}}^{2+}$, ${\mathrm{Pb}}^{2+}$, etc.) or ${\mathrm{ABO}}_3$ compounds. X-ray photoelectron spectra establish the presence of four valent Sn and Mn ions; thus the electrical conductivity is n type rather than p type as for the ${\mathrm{ABO}}_3$ material. Also, x-ray powder diffraction indicates that the crystal structure is monoclinic. Magnetic susceptibility and Mössbauer spectra of ${}_{}{}^{57}{}_{}{}^{}\mathrm{doped}$ samples have also been investigated. Although the resistivity of the iron-doped manganite is now larger, the CMR is actually increased.