Effect of electron doping on the magnetic correlations in the bilayered brownmillerite compound Ca_2.5-xLa_xSr_0.5GaMn₂O₈: a neutron diffraction study

The effect of electron doping on the magnetic properties of the brownmillerite type bilayered compounds has been investigated by neutron powder diffraction in La substituted Ca2.5-xLaxSr0.5GaMn2O8 compounds (x = 0.05 and 0.1), in comparison with the undoped compound (x = 0). In all compounds, a long-range three-dimensional collinear antiferromagnetic (AFM) structure is found below the Néel temperature TN of the respective compound, whereas, well above TN, three-dimensional short-range magnetic ordering is observed. In the intermediate temperature range just above TN, a strong effect of electron doping (La substitution) on the magnetic correlations has been observed. Here, a short-range AFM correlation with a possible dimensionality of three has been found for substituted compounds (x = 0.05 and 0.1) as compared to the reported two-dimensional long-range AFM ordering in the parent compound. With increasing electron doping, a decrease in TN is also observed. The short-range magnetic correlations set in over a large temperature range above TN. A magnetic phase diagram in the x–T plane is proposed from these results