Magnetic, electronic, and thermal transport properties of Eu0.55Sr0.45MnO3

Magnetic, electronic, and thermal transport properties of Eu0.55Sr0.45MnO3 have been experimentally studied. The compound is found to exhibit a complex magnetic behavior with the change of temperature and magnetic field. Without magnetic field, it stays in a Griffiths-like state in a wide temperature range above similar to 100 K, characterized by the presence of ferromagnetic (FM) clusters of the size of similar to 8 Mn ions, and an antiferromagnetic (AFM) state below similar to 100 K, evidenced by thermopower and heat conductivity. FM phase emerges and grows in the AFM matrix with applied field, resulting in a series of phase transitions from the paramagnetic (PM) state first to the AFM state, then to the FM and the AFM states upon cooling (similar to 0.8 T < H <similar to 1 T), or a simple PM-FM transition (H>similar to 2.3 T). The AFM state is unstable under high fields, and the high- and low-temperature AFM transitions are depressed by the fields above similar to 1 and similar to 2.3 T, respectively. The FM transition is incomplete when the field is below similar to 1.5 T, leading to a coexistence of the FM and PM (or AFM) phases in the intermediate temperature range. A spin-glass-like behavior is observed in the AFM background below similar to 50 K. Significant response of resistance, thermopower, and heat conduction to magnetic transition, either FM or AFM transition, has been observed. Unlike the typical AFM manganites, for which usually a depression of thermal conduction occurs at the AFM state, the AFM transition in Eu0.55Sr0.45MnO3 enhances the thermal conduction. From the PM phase to the AFM phase and to the FM phase, thermal conductivity increases monotonically. A remarkable result of the present work is the different behaviors of thermopower and resistivity. The former displays a metallic behavior below a distinct temperature that is significantly lower than the metal-to-insulator transition temperature determined by resistivity. Furthermore, thermopower remains metallic while the resistivity shows up an upturn due to the AFM transition in the low-temperature range under the field of 1.5 T. Based on these data, a magnetic phase diagram is proposed.