Hole-doping dependence of percolative phase separation in Pr0.5-delta Ca0.2+delta Sr0.3MnO3 around half doping - art. no. 134422

摘要

We address the problem of the percolative phase separation in polycrystalline samples of Pr0.5-deltaCa0.2+deltaSr0.3MnO3 for -0.04less than or equal todeltaless than or equal to0.04 (hole doping n between 0.46 and 0.54). 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 T-C. However, for n>0.50 we found that in a wide temperature range below T-C an important PM volume still survives, coexisting with the FM phase. On lowering T below the charge-ordering (CO) temperature T-CO 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 nless than or equal to0.50 the metallic fraction is above the critical percolation threshold X(C)similar or equal to15.5%. As a consequence, these samples show very different magnetoresistance properties. In addition, for nless than or equal to0.50 we observe a percolative metal-insulator transition at T-MI, and for T-MI