Slow Thermodynamics in the Phase Separated State of the Bilayered Manganite (La0.4Pr0.6)1.2Sr1.8Mn2O7

Bilayered perovskite (La0.4Pr0.6)1.2Sr1.8Mn2O7 exhibits a field-induced paramagnetic-insulator to ferromagnetic- metal transition, and a phase-separated state is realized after the field is switched off. In order to clarify the thermodynamic properties of the phase-separated state which is a common feature in many mangan- ites, we performed specific heat measurement with field along the magnetization easy axis. We have revealed that the remanent specifc heat might exhibit a stretched exponential decay and the relaxation time is remarkably long. These results indicate the importance of magnetic frustration originating from the competition between double-exchange interaction and superexchange interaction.