Electron transport and thermoelectric properties of layered perovskite LaBaCo₂O_5.5

We have investigated systematically the physical transport properties of layered 112-type cobaltite by means of electrical resistivity, magnetoresistance and thermopower measurements. In order to understand the complex transport mechanism of LaBaCo₂O_5.5, the data have been analysed using different theoretical models. The compound shows an electronic transition between two semiconducting states around 326 K, which coincides with the ferromagnetic transition. Interestingly, the system also depicts a significant magnetoresistance (MR) effect near the ferro/antiferromagnetic phase boundary and the highest value of MR is close to 5% at 245 K under ± 7 T. The temperature dependence of thermopower, S(T), exhibits p-type conductivity in the 60 K≤T≤320 K range and reaches a maximum value of around 303 µV K⁻¹ (at 120 K). In the low temperature antiferromagnetic region the unusual S(T) behaviour, generally observed for the cobaltite series LnBaCo₂O_5.5 (Ln = rare earth), is explained by the electron magnon scattering mechanism.