Development of Thermoelectric Bi-Based Cobaltites with an Easy Axis of Magnetization Parallel to the C-Axis for Magnetic Alignment

We report the conversion of the easy axis of magnetization from the a -axis to the c -axis in thermoelectric misfit-layered Bismuth-based cobaltites for a magnetic grain-alignment process. The conversion was accomplished by the substitution of Ca for Sr in the block layer of [(Bi 0.5 Pb 0.5 ) 2 Sr 2 O 4 ] 0.55 CoO 2 . Moreover, magnetic anisotropy along the c -axis was enhanced by partial substitution of Pr for Ca in [(Bi 0.5 Pb 0.5 ) 2 Ca 2 O 4 ] z CoO 2 . From the analysis of their crystal structures, we concluded that the doping of Pr and Ca played a role in distortion of the block layer, indirectly leading to changes in the local structure of the CoO 2 layers and magnetic anisotropy. The c -axis grain-aligned bulk has been successfully fabricated by a magnetic grain-alignment method in 10 T, and a drastic reduction in the resistivity perpendicular to the applied field and the grain-oriented microstructure were observed.