Large Low-Field Magnetoresistance in Perovskite-typeCaCu3Mn4O12without Double Exchange

We report the observation of large low-field magnetoresistance (MR) behavior in ${\mathrm{CaCu}}_{3}{\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$ with a perovskite-related $({\mathrm{AA}}^{\ensuremath{'}}_{3}B_{4}{\mathrm{O}}_{12})$ structure. ${\mathrm{Ca}}^{2+}{\mathrm{Cu}}_{3}^{2+}{\mathrm{Mn}}_{4}^{4+}{\mathrm{O}}_{12}$ is semiconducting and orders ferromagnetically at 355 K. However, it has neither mixed valency of Mn for double-exchange magnetic interactions, nor Jahn-Teller ${\mathrm{Mn}}^{3+}$ ions, nor a metal-insulator transition. The MR smoothly increases with decreasing temperature and is $\ensuremath{-}40%$ at 20 K. The low-field MR response does not show the strong temperature-dependent decay characteristic of the ${\mathrm{LnMnO}}_{3}$ perovskite-based systems and appears consistent with an intergrain-interdomain tunneling origin.