Evidence of collective relaxation behavior in the reentrant phase of oxygen-rich LaMnO3

The reentrant low temperature phase of the perovskite manganite LaMnO3+δ (δ=0.22) has been investigated with ac susceptibility and dc magnetization studies. A critical examination of the memory effects in ac susceptibility leads us to the conclusion that the slow dynamics in the system is a consequence of collective relaxation processes resulting from interactions between ferromagnetic clusters, whose presence was indicated in earlier studies. Here, we postulate that the collective behavior is due to the existence of long-range (dipolar) interactions between the large ferromagnetic ‘superspins’. This is also confirmed by an abnormally large microscopic spin-flip time (∼10−9 s) compared to a canonical spin glass.

► Low temperature anomaly in ac susceptibility of LaMnO3+δ. ► Frequency dependence shows slow dynamics with a large relaxation time (10−9 s). ► Occurrence of zero field memory effect shows collective relaxation behavior. ► Dipolar interaction between ferromagnetic clusters.