Discontinuous evolution of the highly distorted orthorhombic structure andthe magnetic order in LaMnO3 +/-delta perovskite

In this work we present a systematic study of the crystallographic structur e and the magnetic ordering of LaMnO3+/-delta perovskites. Changing the oxy gen composition within the range 2.995 < 3 +/- delta < 3.140, we found a 3 + delta(1) value (3.04 < 3 + delta(1) < 3,05) which defines a boundary in t he magnetic phase diagram T vs 3 +/- delta. For 3 + delta < 3 + delta(1), a ntiferromagnetic order is present in the samples with a small ferromagnetic component, while for large 3 + delta values (3 + delta > 3 + delta(1)) the samples are ferromagnetic, The transition from one region to the other is associated with a change in volume of around 1%, (C) 1999 Academic Press.