Enhancement of the spin entropy in NaxCo2O4 by Ni doping

Abstract

The effects of Ni doping on the spin entropy in NaxCo2O4 (x=1.2) has been carefully studied. A strong magnetic-field suppression of the thermopower indicates the emergence of large spin-entropy effect. The magnetothermopower increases with increasing Ni doping level, suggesting that Ni doping improves the spin entropy of NaxCo2O4. Based on analysis of x-ray absorption spectra, we propose a spin-entropy competition mechanism to explain well the spin-entropy enhancement.