Low-field magnetic properties of LaMnO3+δ with 0.065 ≤ δ ≤ 0.154

In a weak (B = 2 G) magnetic field LaMnO3+delta exhibits at delta = 0.065 below the paramagnetic-to-ferromagnetic (FM) Curie temperature, T-C, a mixed (spin-glass and FM) phase followed by a frustrated FM phase at delta between 0.100 and 0.154. The same behavior is observed in La1-xCaxMnO3 with x between 0 and 0.3. This can be understood by the similar variation of the Mn4+ concentration, c between approximate to 0.13 and 0.34, in both materials when x or delta is increased. On the other hand, considerable differences are found between these compounds in the values of the magnetic irreversibility, in the dependencies of T-C(c) and the magnetic susceptibility, chi(c), as well as in the critical behavior of chi(T) near T-C. These differences can be explained by distortions of the cubic perovskite structure, by the reduced lattice disorder and by the more homogeneous hole distribution in LaMnO3+delta than in La1-xCaxMnO3. (C) 2003 Elsevier Ltd. All rights reserved.