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 $\left({\mathrm{AA}}^{\prime }{}_3{}^{}{}_{}{}^{}B_4^{}{}_{}{}^{}{\mathrm{O}}_{12}\right)$ 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 $-40\mathrm{}\%$ 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.

• Received 5 October 1998

DOI:https://doi.org/10.1103/PhysRevLett.82.3164