Orbital correlations and magnetic phase transitions in lightly doped La0.88MnOx and LaMn0.94Oy manganites

The results of X-ray and neutron diffraction study as well as the elastic, magnetic, and electrotransport properties of La0.88MnOx (2.82 less than or equal to x less than or equal to 2.96) and LaMn0.94Oy (2.91 less than or equal to y less than or equal to 3.00) manganites have been presented. Under oxygen doping, the transitions from antiferromagnetic to ferromagnetic or spin-glass state are observed for La-deficient and La-excessive series, respectively. These transitions have been found to correlate with the change of the type of Jahn-Teller distortions from static to dynamic ones. The dynamic orbital correlations favor a ferromagnetic state, while an A-type antiferromagnetic state is typical of the static Jahn-Teller distortions. It is argued that the canting magnetic structure in manganites is not realized. The transition to a ferromagnetic or spin-glass state occurs via the formation of inhomogeneous state with different types of orbital correlations and magnetic structure. The key role of intrinsic chemical inhomogeneity in the formation of inhomogeneous magnetic states in solid solutions of manganites is emphasized.