Nature of short-range ferromagnetic ordered state above T_c in double perovskite La_2NiMnO_6

摘要

Magnetic measurements of La_2NiMnO_6 reveal that its inverse susceptibility exhibits an upward derivation from Curie-Weiss behavior above T_c, indicating the presence of a short-range ferromagnetic ordered state. It is suggested that the upward derivation is due to antiferromagnetic interactions arising from anitisite defects, which is supported by the magnetic studies on the samples where the antiferromagnetic interactions are modulated by partially doping La with Sr or by decreasing the sample size. Basing on these results, we propose that the short-range ferromagnetic ordering is induced by antisite defects against long-range ferromagnetic ordering of the Ni/Mn sublattice.