Lu-induced spin entropy enhancement in Ca3Co4O9+δ system

The magnetothermopower have been studied in Lu-doped Ca3−xLuxCo4O9+δ. A strong magnetic field suppression of thermopower indicates large spin entropy contribution. The magnetothermopower for doped samples are overall enhanced compared with that for undoped Ca3Co4O9+δ, providing an experimental evidence for the enhancement of spin entropy. Magnetic results confirm that Co4+ concentration is reduced by Lu doping. We suggest that the reduction in Co4+ concentration results in the enhanced spin entropy.