We have synthesized various ferromagnetic (FM) perovskite manganese oxides, La0.7Ca0.3-xSrxMnO3 (x = 0.0, 0.1, 0.2, 0.3), using PMMA colloidal spheres as a template. In this method, the corresponding precursor solution infiltrates into the interstitial voids of a crystal template and solidifies without disrupting the parent framework. The resulting porous network, after sintering at 800 oC, is composed of nanometer-sized FM wires with three dimensionally ordered spherical voids, which were evidenced by SEM, TEM, X-ray powder diffraction, and magnetization measurements. The average diameter of the pores is approximately 350 nm, which is about 15 % smaller than that of the parent PMMA colloids, indicating that the polymer/oxide composite underwent shrinkage during sintering. As the Sr content increases, the Curie temperature (Tc) gradually rises up to 350 K. All the samples exhibit a metal-insulator transition near Tc. Moreover, they show large negative magneto resistances below Tc, which might be ascribed to spin-polarized tunneling at the nanometer-sized grain boundaries. The porous FM oxide proves very valuable in making various nano-hybrid materials simply by filling the pores with other functional oxides.
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