Evidence of spin frustration in LaMnO_3+δ with δ = 0.0 and 0.025

We measured the ac susceptibility and the dc magnetization of LaMnO_3+δ with δ = 0.0 and 0.025. The ac susceptibility showed a clear frequency dependence near the Neel temperature T_N for both samples. Furthermore, the dc magnetization showed that LaMnO_3.0 had a non-zero isothermal remanent magnetization below 140 K. From both measurements, we conclude that the antiferromagnetic transition of LaMnO_3+δ is accompanied by the development of an order parameter of ferromagnetic nature, which has almost the same transition temperature as T_N. We discuss our results in terms of a possible phase coexistence at a microscopic level.