Comparison of DC resistivity and microwave transport properties of preferentially de-oxygenated polycrystalline La0.67Ca0.33MnO3

Abstract With the aim of finding a simple route to enhancement of the low field, magnetoresistive effect in manganites, polycrystalline samples of La 0.67 Ca 0.33 MnO 3 with different density and grain size were preferentially deoxygenated in defective regions (pores and grain boundaries). A combination of DC and 9 GHz microwave transport measurements were undertaken to identify the influence of the deoxygenation on the magnetotransport properties. It was found that interconnected porosity provides the dominant, preferential deoxygenation path in our samples. The sample density, and hence level of interconnected porosity influenced the reducing annealing conditions required to preferentially deoxygenate grain boundary regions. Hence, by paying attention to sample microstructure, we were able to control preferential deoxygenation. In the more porous sample we produced enhanced, low field, grain boundary magnetoresistance effects.