Dynamics of the lattice and spins in the phase-separated manganite (Eu_1−xGd_x)_0.6Sr_0.4MnO₃

We investigated slow relaxations of the magnetostriction and residual magnetostriction of the phase-separated system (Eu_1−xGd_x)_0.6Sr_0.4MnO₃, in which the metamagnetic transition from a paramagnetic insulating state to a ferromagnetic metallic state is accompanied by a lattice shrinkage. The relaxations are well fitted by a stretched exponential function, suggesting the strong frustration between the double exchange interaction and Jahn-Teller effect. We have revealed that the Gd substitution suppresses the frozen phase-separated phase at low temperatures and stabilizes the paramagnetic insulating state in the dynamic phase-separated phase at intermediate temperatures. The former origin would be the randomness effect and the latter would be the suppression of the double exchange interaction.