Magneto-transport in orthocobaltite GdBaCo2O5.5

Magnetic and transport measurements have been carried out for GdBaCo2O5.5. The appearance of the ferromagnetic component of magnetization above the Neel temperature has been confirmed. The temperature dependence of the magneto-resistivity, having maximum at the Neel and Curie temperatures, was shown to be strongly correlated with the temperature dependence of magnetization. The temperature dependence of the electrical resistivity has been evidenced to be of the semiconducting type with an activation energy exceeding 45 meV. The resistivity data has favored the polaronic type conductivity models. It was shown that the thermoelectric power was correlated with the electrical resistivity of GdBaCo2O5.5, and its sign indicated on the contribution of the orbital degrees of freedom. The phonon-mediated heat transport was also affected by magnetic field as indicated by the slope of temperature dependence of thermal conductivity, varying about 240 K. The experimental results are discussed with theoretical models and compared to other magneto-resistive systems.