Ferro- and antiferromagnetic ordering in LaMnO3+delta

A neutron diffraction study of the crystalline structure and magnetic state of LaMnO3+delta samples with different deviations from oxygen stoichiometr y has been made at 4.2 K. It is shown that annealing at reduced oxygen pres sure is accompanied by transformation of the magnetic structure from ferrom agnetic, with magnetic moments parallel to the b axis, to antiferromagnetic , with the wave vector k=0 and the moments along the a axis (space group Pn ma). A comparison of experimental with expected Mn ion moments suggests tha t magnetic order does not extend throughout the sample volume. Part of the Mn ions form magnetic clusters similar to 20 Angstrom in size. (C) 1999 Ame rican Institute of Physics. [S1063-7834(99)02201-7].