Large magnetoresistance in three dimensionally ordered macroporous perovskite manganites prepared by a colloidal templating method

Macroporous perovskite manganites La_0.7Ca_0.3-xSr _xMnO₃, whose pores are highly ordered, have been prepared by a colloidal templating technique. The pore size was found to be about 400 nm and the wall thickness was in the range of 40-60 nm. As the Sr content increased, the ferromagnetic transition temperature (Tc) gradually rose to 350 K. The x = 0.1 sample exhibited a metal-insulator transition near T_C. A large negative magnetoresistance (MR), which was independent of temperature, was also observed below T_C. The large MR might be ascribed to spin polarized tunneling at the nano-sized grain boundaries.