Orbital Correlations and Magnetic Phase Transitions in Lightly Doped La 0.88 MnO x and LaMn,dwi{0.94}>O y Manganites

I.O. Troyanchuk a , V.A. Khomchenko a , M. Tovar b , H. Szymczak c and K. Bärner d a Institute of Solid State and Semiconductor Physics National Academy of Sciences, P. Brovka str. 17, 220072 Minsk, Belarus b Hahn-Meitner-Institute (BENSC), Glienickerstr. 100, 14109 Berlin, Germany c Institute of Physics, Polish Academy of Sciences al. Lotników 32/46, 02-668 Warsaw, Poland d IY. Physikalisches Institut der Universität Göttingen Bunsenstrasse 13-15, 37073 Göttingen, Germany

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The results of X-ray and neutron diffraction study as well as the elastic, magnetic, and electrotransport properties of La 0.88 MnO x (2.82<= x<= 2.96) and LaMn 0.94 O y (2.91<= y<= 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.

DOI: 10.12693/APhysPolA.105.27 PACS numbers: 75.30.Kz, 75.47.Lx, 61.50.Ks