Magnetic relaxation and phase separation in manganite Eu0.55Sr0.45MnO3

We present a study of the magnetic relaxation behavior of the phase-separated manganite Eu0.55Sr0.45MnO3. A local maximum of the magnetic viscosity S is observed around the magnetic freezing temperature and near the Curie temperature, respectively. The former is ascribed to relaxation of the proportion of coexisting ferromagnetic and non-ferromagnetic phases from a magnetic frozen matrix. A quantitative relation established between S and the initial normalized magnetization before relaxation, m, shows that S keeps constant at low m values, reaches a broad maximum around m∼0.35, then decreases rapidly, and finally remains at nearly zero for m>0.7. The latter local maximum of S, much smaller than the former in magnitude, is possibly associated with both the relaxation of the proportion of coexisting phases and the reorientation of magnetic moments in ferromagnetic domains. Thermoelectric and magnetic relaxation results further indicate the existence of a definite temperature Tthermo between which and the metal-insulator transition Tp magnetic inhomogeneity is significant. Based on these results, a temperature and field dependent scenario of phase separation in Eu0.55Sr0.45MnO3 is proposed.