Controlled phase separation in La0.5Ca0.5MnO3

A systematic study of phase separation effects in polycrystalline La0.5Ca0. 5MnO3 obtained under different thermal treatments is reported. Samples with average grain size ranging from 200 to 1300 nm were studied. Magnetic and electrical measurements show quantitative differences among samples in thei r low-temperature behavior, indicating that the fraction of the ferromagnet ic (FM) phase gradually decreases as the grain size increases. Percolation of the FM phase in samples with a small fraction of this phase suggests tha t grain boundaries play a distinctive role in the spatial distribution of c oexisting phases. The defective structure at the grain surface could explai n the local inhibition of the antiferromagnetic charge ordered phase, an ef fect that is gradually removed with increasing grain size. Qualitative agre ement of the data with this description is found. This effect is also found to be highly dependent on the oxygen content of the samples and its spatia l distribution.