Hole-doping dependence of percolative phase separation in (formula presented) around half doping

We address the problem of the percolative phase separation in polycrystalline samples of (formula presented) for (formula presented) (hole doping n between (formula presented) and (formula presented) We perform measurements of x-ray diffraction, dc magnetization, electron spin resonance (ESR), and electrical resistivity. These samples show a paramagnetic (PM) to ferromagnetic (FM) transition at the Curie temperature (formula presented) However, for (formula presented) we found that in a wide temperature range below (formula presented) an important PM volume still survives, coexisting with the FM phase. On lowering T below the charge-ordering (CO) temperature (formula presented) all the samples exhibit a coexistence of the FM metallic and CO (antiferromagnetic) phases. In the whole T range the FM phase fraction (X) decreases with increasing n. Furthermore, we show that only for (formula presented) the metallic fraction is above the critical percolation threshold (formula presented) As a consequence, these samples show very different magnetoresistance properties. In addition, for (formula presented) we observe a percolative metal-insulator transition at (formula presented) and for (formula presented) the insulating-like behavior generated by the enlargement of X with increasing T is well described by the percolation law (formula presented) where t is a critical exponent. On the basis of the values obtained for this exponent we discuss different possible percolation mechanisms, and suggest that a more deep understanding of geometric and dimensionality effects is needed in phase separated manganites. We present a complete T vs n phase diagram showing the magnetic and electric properties of the studied compound around half doping.